Antibiotic Resistance
The Warning Fleming Gave in His Nobel Lecture
- 8 chapters
- 49m
- Infectious & Chronic Disease
- Free · no sign-up
This book explains how resistance spreads through bacterial genes, particularly through plasmids that move between cells. It covers β-lactam antibiotics and how they work, why poultry and livestock farming use so many antibiotics, and how this contributes to multiple drug resistance in human pathogens. The book also explores emerging infectious diseases and rare conditions like Whipple's disease.
Anyone who has ever wondered why doctors prescribe a full course of antibiotics or how a common infection can become untreatable will find this explanation essential reading.
Listen
-
Read this chapter
Overview
Antimicrobial resistance, or AMR, happens when germs evolve ways to survive antimicrobial drugs used to treat infections in humans, animals, and plants. This includes bacteria, viruses, parasites, and fungi, all of which can become resistant, a problem affecting everyone globally. Misuse of these drugs drives resistance, though it can also occur naturally through genetic changes and gene spread. The World Health Organization says AMR is among the top threats to global health, with 1.27 million deaths directly linked to bacterial resistance in 2019 and over 4 million in 2021. Infections caused by resistant microbes are harder to treat and often require expensive alternatives with more side effects. By 2050, without action, the WHO warns up to 10 million people could die yearly from AMR. Israeli scientists announced in 2026 that they had found bacteria capable of creating dozens of copies of genes helping them resist antibiotics.
Definition
Antimicrobial resistance happens when microbes like bacteria, fungi, viruses, or parasites stop responding to drugs meant to kill them. This resistance is a microbe trait, not a person's condition. When organisms become resistant, antimicrobial drugs can no longer treat infections caused by them. Antibiotic resistance is one kind of this broader issue, specifically linked to bacteria. It breaks down into microbiological and clinical resistance. Microbiological resistance comes from mutated or inherited genes that help bacteria survive antibiotic treatments. Clinical resistance shows up when bacteria that were once killed by treatment start surviving it instead. In both cases, bacteria can share resistance through horizontal gene transfer—via conjugation, transduction, or transformation—which allows the trait to spread among similar bacterial species.
Overview
The World Health Organization reported in April 2014 that antibiotic resistance is no longer a future threat but a present danger affecting every region of the world. In 2024, nearly 5 million deaths were linked to antimicrobial resistance, with 1.27 million of those occurring in children under five. The WHO identified antibiotic resistance as one of the greatest threats to global health, food security, and development in 2018. That same year, the European Centre for Disease Prevention and Control found that in 2015, 671,689 infections caused by resistant bacteria led to 33,110 deaths across the EU and European Economic Area, most acquired in healthcare settings. By 2019, the death toll from AMR had risen to 133,000. As the WHO stated, "this serious threat is no longer a prediction for the future, it is happening right now in every region of the world and has the potential to affect anyone, of any age, in any country." Antibiotic resistance occurs when bacteria change, making antibiotics ineffective against infections that once could be treated.
Causes
Antimicrobial resistance (AMR) occurs primarily due to antibiotic misuse and overuse. The NIAID explains that microbes reproduce rapidly and adapt, sometimes changing their survival capabilities. Limited access to essential antimicrobials forces microbes to develop defenses or allows naturally resistant strains to proliferate. Mutations help individual microbes survive exposure, and while rare, frequent reproduction increases resistance development chances. About 1 in 3 antibiotic prescriptions may be unnecessary—around 154 million are written yearly, with up to 46 million being inappropriate. Some bacteria resist antibiotics through phenotypic tolerance and DNA repair rather than mutation. Stopping treatment early leaves resistant microbes behind. Bacteria also share resistance genes via horizontal gene transfer, spreading drug resistance rapidly between species. Over the past 20 years, AMR has made common infections harder to treat, while new antibiotics aren't being developed fast enough to keep up. Without global action, basic medical procedures could become dangerous.
Natural occurrence
Antimicrobial resistance is a natural process that happens when microbes are exposed over time to substances that fight them. As organisms adapt, those with resistance survive and pass on their traits, making resistant types more common in the environment. Some resistances, like methicillin resistance, appeared before humans used antibiotics—possibly as a co-evolutionary trait in hedgehogs infected by dermatophytes that produce antibiotics. Alexander Fleming discovered penicillin, but even the natural penicillins he found lost effectiveness quickly in human treatments. Resistance can also spread between microbes through horizontal gene transfer, where genes move from one organism to another. This helps explain how a microbe that doesn’t usually cause disease might become dangerous if it gains resistance genes. The more we use antimicrobials, the faster this natural process speeds up.
Self-medication
Self-medication with antibiotics is a widespread practice, especially in resource-limited countries, and it's one of the main drivers of antimicrobial resistance. In many places, people take medicines on their own or based on advice from others without medical training, which is dangerous. This is common in countries like India, where 73% of the population uses self-medication for minor and chronic health issues, often because doctors are hard to reach or too expensive. Studies show that even though 70% of people surveyed had heard of antibiotic resistance, 88% misunderstood it as a change in the human body rather than a microbial issue. Factors like easy access, lack of awareness, and poor healthcare conditions contribute to this problem.
Clinical misuse
Clinical misuse by healthcare professionals contributes significantly to antimicrobial resistance. Studies in the U.S. found that up to 50% of antibiotic treatments had incorrect indications, choices, or durations. In 2010 and 2011, about a third of outpatient prescriptions were unnecessary. A French ICU study showed 30% to 60% of antibiotics prescribed were not needed. Research also revealed that only 63% of physicians surveyed considered antibiotic resistance a problem in their practice, while 23% believed aggressive prescribing was necessary to avoid inadequate care. Some doctors may overprescribe for legal reasons, even when clinical need is unclear. Misconceptions about antibiotics treating mild illnesses fuel their overuse. Veterinary oversight is required by law for important antibiotics, and veterinarians use a PK/PD model to ensure proper dosing.
Pandemics, disinfectants and healthcare systems
During early COVID-19 waves, increased antibiotic use may have worsened antimicrobial resistance, while healthcare system strain contributed to more resistant infections. Widespread disinfectant use like alcohol-based hand sanitizers might promote resistance through mutations. Conversely, better hand hygiene, fewer international travels, and reduced elective hospital procedures likely slowed spread of resistant pathogens short-term. Critically ill patients needing antimicrobials face increased resistance risk. AMR pressures health systems and economies—global losses could reach $3.4 trillion annually by 2030, with healthcare costs rising $1 trillion by 2050. A 2024 UN meeting pledged to reduce deaths from bacterial AMR by 10% over six years and committed $100 million to update action plans, though a target to cut antibiotic use in animals by 30% by 2030 was removed due to opposition from meat-producing countries and the farming industry.
-
Read this chapter
Overview
Beta-lactam antibiotics are a major group of medicines that include penicillin and its relatives, like cephalosporins and carbapenems, all built around a specific chemical ring called the beta-lactam ring. These drugs work by stopping bacteria from building cell walls, and for decades they were the most widely used antibiotics, with more than half of all commercial antibiotics being beta-lactams until 2003. The first of these, penicillin, came from a fungus called Penicillium rubens—then known as Penicillium notatum. Bacteria can fight back by producing an enzyme called beta-lactamase that breaks the beta-lactam ring, but scientists have countered this by combining beta-lactam antibiotics with inhibitors like clavulanic acid.
Medical use
Beta-lactam antibiotics are used to treat and prevent bacterial infections caused by susceptible organisms. Initially, these drugs were mainly effective against gram-positive bacteria, but recent advances have led to broad-spectrum versions that also target gram-negative organisms, greatly expanding their usefulness. When it comes to the brain, specifically the meninges in normal, non-inflamed conditions, beta-lactam antibiotics don’t penetrate well—only about 0.15 of the ratio of cerebrospinal fluid to serum drug levels.
Adverse drug reactions
β-lactam antibiotics, a class of drugs that includes penicillins and cephalosporins, can cause a range of side effects in patients. Common reactions include digestive issues like diarrhea and nausea, as well as skin problems such as rash and urticaria. Sometimes, these medications can lead to superinfections, including candidiasis. Less frequent but still possible are fever, vomiting, erythema, dermatitis, angioedema, and pseudomembranous colitis. For those receiving β-lactams through injection, pain and swelling at the injection site are also frequent concerns.
Allergy/hypersensitivity
About ten percent of people taking β-lactam antibiotics might have an immune system reaction, though only a small part of those are true IgE-mediated allergies. Anaphylaxis happens in roughly 0.01% of patients. There’s possibly a five to ten percent chance of cross-sensitivity between penicillin, cephalosporins, and carbapenems, although some researchers have questioned that figure. Still, because of this risk, all β-lactam antibiotics are contraindicated for anyone who has had severe reactions like urticaria, anaphylaxis, or interstitial nephritis to any β-lactam. Rarely, allergic responses have been triggered by contact such as kissing or sexual activity with someone taking these drugs. A Jarisch–Herxheimer reaction can also occur after starting treatment for syphilis with a β-lactam antibiotic.
Inhibition of cell wall synthesis
β-Lactam antibiotics kill bacteria by blocking the formation of their cell walls, specifically by interfering with a process called transpeptidation, which is key to building peptidoglycan, the main structural component of bacterial cell walls. These drugs mimic a piece of the peptidoglycan precursor, called d-alanyl-d-alanine, and bind tightly to enzymes known as penicillin binding proteins or PBPs, permanently disabling them. This prevents the cross-linking needed for cell wall strength, leading to cell death. The antibiotics also affect the division of organelles like chloroplasts and cyanelles, but not plastids in more complex plants, supporting the theory that these organelles evolved from bacteria through endosymbiosis. Normally, when peptidoglycan precursors build up due to this blockage, they trigger enzymes that break down existing cell wall material, making the antibiotic action even stronger.
Guanine oxidation
One explanation for how β-lactam antibiotics cause cell death involves changes to guanine within bacterial DNA. When oxidized guanine gets built into DNA, it can trigger toxicity. If the cell doesn’t fully repair closely positioned 8-oxo-2'-deoxyguanosine damage, that leads to double-strand breaks in the genetic material.
Potency
The effectiveness of β-lactam antibiotics relies on two specific structural elements. One is referred to as "Woodward's parameter", h, which describes the height, in angstroms, of a pyramid formed by the nitrogen atom of the β-lactam ring and the three neighboring carbon atoms. The other is known as "Cohen's parameter", c, measuring the distance between the carbon of the carboxylate group and the oxygen of the β-lactam carbonyl. This distance is thought to align with the interaction between the antibiotic and the PBP enzyme. Antibiotics that perform best typically show higher h values, indicating greater reactivity to hydrolysis, and lower c values, suggesting better binding to PBPs.
Modes of resistance
All β-lactam antibiotics share a common structural feature: the β-lactam ring. For these drugs to work, they must reach their target intact and bind properly to penicillin-binding proteins, or PBPs. Bacteria can resist these antibiotics in two main ways. First, they may produce enzymes that break down the β-lactam ring. Second, they can possess PBPs that are altered in a way that prevents the antibiotic from binding effectively. These resistance mechanisms allow bacteria to survive exposure to drugs like penicillin, which were once powerful tools in fighting infection.
-
Read this chapter
Overview
Since their approval by the Food and Drug Administration in 1951, antibiotics have been widely used in large quantities in U.S. poultry farming. Three years earlier, scientists observed that chickens exposed to bacteria-rich manure seemed healthier. Tests showed that chickens fed vitamin B12 produced with residue from a specific antibiotic grew 50% faster than those fed B12 from another source. Further research confirmed that antibiotics improved chicken health, leading to higher egg production, lower death rates, and fewer illnesses. As demand grew, farmers turned to antibiotics because they made chickens reach market weight faster and at a lower cost. This practice differs from Europe, where growth-promoting antibiotics were banned in the 1950s. Recently, this widespread use has raised concerns about bacterial resistance.
Emerging threats: antibiotic resistance
The Centers for Disease Control and Prevention has identified antibiotic resistance as a national threat. In 2016, over 70% of FDA-approved antibiotics were being used in modern, high-production poultry operations to manage disease. The FDA reported that in 2009 alone, 29 million pounds of antibiotics were used in livestock. Surveillance of how consumers are exposed through poultry consumption is limited. By 2012, the FDA had expressed concern that the greatest public health risk from antimicrobial use in animals was the spread of resistant bacteria to humans. These warnings have been challenged by industry lobbyists who argue that antibiotics are used responsibly and judiciously to preserve their effectiveness.
Consumer health effects
When people eat poultry products, they can be exposed to antibiotic-resistant bacteria transferred from animals through the food supply. The CDC acknowledged this in their 2013 report on antibiotic resistance in the U.S. One in six Americans gets sick from foodborne illness each year, and antibiotics are vital for preventing deaths. A literature review found that 100 out of 139 studies showed a connection between animal antibiotic use and human resistance. In poultry farming, antibiotics like fluoroquinolones and penicillin are commonly used, which are also first-line treatments in humans. If those don't work, stronger, more toxic antibiotics must be used—limiting options for patients. Treatment for resistant infections starts an average of 72 hours after diagnosis, compared to 11.5 hours for non-resistant ones, increasing risk of severe illness and death. Each year, about 23,000 people die from resistant infections, especially those in high-risk groups like the elderly or immunocompromised.
Vertical integration
In the 1940s, as antibiotics began being used in livestock feed, a new system took hold in the chicken industry, one that Perdue is credited with pioneering. This structure, called vertical integration, centers production under large companies known as "integrators." These integrators control everything from feed formulas to antibiotic use, and they own the birds while farmers, called "growers" or "operators," manage the land and buildings where the chickens are raised. Growers are guaranteed payment based on how much weight each flock gains. Because of this setup, about 90% of broilers are raised within 60 miles of a processing plant. By 2011, just twenty of these integrators controlled 96% of all broilers produced in the U.S.
Regulatory surveys
The USDA runs two main surveys to help regulate farming, the Agricultural and Resource Management Survey, or ARMS, and the National Animal Health Monitoring Survey, known as NAHMS. ARMS is managed by the USDA's Economic Research Service and National Agricultural Statistics Service. It looks at the financial side of farming, how animals are raised, and what resources are used. The most recent version for broiler farmers was done in 2006 and 2011. One question in those surveys asked about using antibiotics in poultry feed or water, but only for growth promotion, not for treating illness.
Antibiotic-resistant outbreaks from poultry meat
In order to prevent antibiotic residues in chicken meat, birds given antibiotics must have a withdrawal period before slaughter. The FSIS randomly tests poultry at slaughter and finds very few violations, yet even these small amounts have led to resistant outbreaks. Three of the five pathogens responsible for 90% of foodborne deaths are consistently found in poultry: Salmonella, Campylobacter, and Escherichia coli. In 2014, a Salmonella outbreak affected 634 people across 29 states, with 38% hospitalized, linked to chicken from Foster Farms sold at Costco. Forty-four out of sixty-eight isolates were resistant to at least one drug, and 80% of chicken samples tested showed resistance. Then in 2015, another Salmonella outbreak struck 15 people across seven states, with four hospitalized, traced to frozen stuffed chicken made by Barber Foods.
Limitations and challenges
The U.S. poultry industry is so vertically integrated that many farmers don't know what's in their feed, including whether antibiotics are included. There's no standard way to classify bacteria as resistant or susceptible based on specific antibiotics used. The U.S. is the world's largest producer and second-largest exporter of poultry meat, with 36.9 billion pounds produced and 6.8 billion pounds exported in 2010, valued at around $45 billion. Since the 1970s, agricultural and pharmaceutical industries have lobbied against laws limiting non-therapeutic antibiotic use in livestock. The National Chicken Council argues there's not enough proof of harm to humans and blames overprescribing in medicine instead. If restrictions were put in place, integrators would face immediate financial changes, and public health agencies may lack the research funds needed for effective decisions. America spends about $101 billion a year on health-related research, only five percent of total health expenditures.
Solutions
In 2013, the DATA Act aimed to improve records on antibiotic use in U.S. poultry farming, while PAMTA sought to ban medically important antibiotics in livestock. The 2015 PARA Act required drug companies to prove their antibiotics don’t worsen resistance in humans. Antimicrobial Stewardship Programs show how data can be monitored across sectors. Some producers have turned to hygiene improvements and alternatives like enzymes and probiotics. Sweden banned antibiotics in feed in 1985 without increasing use elsewhere. Perdue began removing all medically important antibiotics from its hatcheries in 2007, labeling products “no antibiotics ever,” and later expanded the label to other brands.
-
Read this chapter
Overview
Antibiotic use in livestock includes treating sick animals, managing infections in groups, and preventing disease—actions that support animal health and food safety. But when used irresponsibly, these drugs can fuel antibiotic resistance, threatening both human and environmental health. Worldwide, about 73% of antimicrobials are used on farm animals, with global agricultural use expected to rise by 67% from 2010 to 2030, especially in developing BRIC countries. In 2017, the World Health Organization urged reducing antibiotic use in food-producing animals. The European Union banned antibiotics for growth promotion in 2006, and the U.S. stopped using sub-therapeutic doses of medically important antibiotics for growth in animals starting January 1, 2017, through changes by the Food and Drug Administration.
History
Since the 1930s, antibiotics have shaped both medicine and farming. Initially used during World War II to treat bovine mastitis, they soon spread across food production — on farms, in fishing fleets, and processing plants. By the late 1940s, studies showed that adding antibiotics to animal feed improved growth and feed efficiency, especially as prices fell. This led to their routine use at low levels to boost output, matching the rise of larger, more confined farms where preventative treatments became standard. Though antibiotic use in the UK was banned in 2006, in 2017, 73% of all antibiotics sold globally were used in food-producing animals.
Genetic Basis of Antibiotic Resistance
Antibiotic resistance is part of a broader issue called antimicrobial resistance, which happens when microbes like bacteria, viruses, fungi, and parasites evolve to survive treatments meant to kill them. This threat is growing, especially as resistance spreads in both rich and poor countries. Bacteria have natural ways to adapt, using genetic plasticity to change either through mutations or by taking in foreign DNA. One key way they gain resistance is through processes like transformation, transduction, and conjugation — especially conjugation, where plasmids help bacteria share survival genes. Resistance isn’t new; it’s been found in ancient environments, even in woolly mammoth remains and polar ice, showing that bacteria can develop resistance naturally, even without human influence.
High priority antibiotics
The World Health Organization updated its list of critically important antimicrobials for human medicine in 2019, aiming to guide strategies that slow resistance and preserve current treatments. It identified third, fourth, and fifth-generation cephalosporins, glycopeptides, macrolides, ketolides, polymyxins like colistin, and quinolones including fluoroquinolones as highest priority. The European Medicines Agency also categorized antibiotics used in animals, separating those with the greatest risk to human health. They labeled quinolones, third and fourth generation cephalosporins, and polymyxins as Category B — "Restrict," meaning only for last-resort use. Macrolides were placed in a new “Caution” category, although evidence shows few cases of transfer from animals to humans, with most human pathogens originating in people.
Sources of antibiotic resistance
While human medical use of antibiotics is the main source of resistant infections in people, humans can also pick up resistance genes from animals like farm livestock, pets, and wildlife. Much resistance comes from overuse in animal farming. Scientists have identified three ways agricultural use might lead to human disease: direct infection from animal bacteria, spread across species barriers, and transfer of resistance genes from farm animals into human pathogens. Although evidence exists for all three pathways, the scale is often limited or hard to prove. As Chang et al. (2014) note: "The topic of agricultural antibiotic use is complex." They say concerns are valid but the extent may be exaggerated, and we should focus on proper use in all areas, especially clinical medicine. The future of antibiotic use in livestock depends on cooperation between local governments and farm workers. A new method called the Livestock Biomass Conversion (LBC) technique helps track antibiotic usage and supports efforts to reduce resistance.
Health issues
Using antibiotics in food-producing animals has become a major health concern, highlighting the deep connections between human, animal, and environmental well-being. This practice plays a key role in driving the development and spread of antimicrobial resistance, which can affect numerous biological systems and pathways.
Human health implications
Antibiotic-resistant bacteria from livestock can move to humans through food, animal contact, or the environment. Pathogens like Salmonella, Campylobacter, and some E. coli strains linked to animal farming cause infections in people that are harder to treat. What makes this worse is that resistance genes can jump between different types of bacteria, spreading the problem beyond just one species or place.
Animal health and agricultural practices
In some areas, antibiotics are given to animals not just to cure illness but also to help them grow faster. These medicines treat, prevent, and control disease in livestock, which can boost animal health and productivity. However, when antibiotics are used too much or in the wrong way, they speed up the development of germs that no longer respond to treatment. This makes it harder for vets to manage infections over time, raising concerns about animal welfare and food safety.
-
Read this chapter
Overview
Multiple drug resistance, or MDR, is a type of antimicrobial resistance where a microorganism can survive exposure to at least one drug from three or more different antimicrobial categories. These categories are defined by how the drugs work and which organisms they target. The most concerning forms of MDR involve bacteria that resist several antibiotics, though MDR can also occur in viruses and parasites, making them resistant to a wide range of antifungal, antiviral, and antiparasitic treatments.
Terminology
When scientists began to see how bacteria were evolving to resist multiple antibiotics at once, they needed new terms to describe the severity of that resistance. In 2011, two such terms were introduced: extensively drug-resistant, or XDR, which means a bacterium is resistant to all antimicrobial drugs except two or fewer categories. Within that category, there's also pandrug-resistant, or PDR, which describes bacteria that are resistant to every single antimicrobial agent in every category. These definitions help doctors and researchers better understand and track the spread of superbugs that no longer respond to treatment.
Antifungal resistance
Yeasts like Candida can grow resistant when treated with azole drugs over long periods, forcing doctors to switch to different medications. In some cases, infections caused by Lomentospora prolificans are so severe that they prove fatal due to the fungus's ability to resist multiple antifungal treatments.
Antiviral resistance
HIV shows how quickly viruses can develop resistance to antiviral treatments, especially when only one drug is used. The influenza virus has also grown resistant over time—first to amantadines, then to neuraminidase inhibitors like oseltamivir, with 98.5% of Influenza A cases showing resistance during the 2008–2009 season. These resistant strains are more common in people whose immune systems are already weakened. Cytomegalovirus can become resistant to ganciclovir and foscarnet when patients receive long-term treatment, particularly those who are immunosuppressed. Herpes simplex virus rarely develops resistance to acyclovir, but when it does, it often involves cross-resistance to famciclovir and valacyclovir, again mostly in immunocompromised individuals.
Antiparasitic resistance
The most striking case of multiple drug resistance in antiparasitic treatment is malaria. The parasite Plasmodium vivax developed resistance to chloroquine and sulfadoxine-pyrimethamine several decades ago. By 2012, Plasmodium falciparum had also begun showing resistance to artemisinin in parts of western Cambodia and western Thailand. Toxoplasma gondii, another parasite, can develop resistance to artemisinin, as well as to atovaquone and sulfadiazine, though it rarely becomes multiply resistant. Resistance in antihelminthic drugs is more commonly reported in veterinary contexts, especially related to how livestock are treated with deworming medications, and has recently drawn attention from the FDA.
-
Read this chapter
Overview
Plasmid-mediated resistance spreads antibiotic resistance genes through plasmids, which are small DNA circles that replicate independently and ensure their own inheritance during cell division. These plasmids can move between bacteria through a process called conjugation, allowing transfer across different genera and kingdoms. Some plasmids include addiction systems that kill cells that don’t inherit them, ensuring they're passed on. Often carrying multiple resistance genes, they contribute to multidrug resistance, especially in Gram-negative bacteria like those in the Enterobacteriaceae family. The global spread of these MDR plasmids has been driven by antimicrobial use in medical settings and agriculture.
Properties of resistance plasmids
Resistance plasmids are small pieces of DNA that carry genes allowing bacteria to resist antibiotics, and they’re not alone in what they bring—often packed alongside are genes that help the bacteria cause disease or fight heavy metals. These resistance genes are usually grouped together in sections called cassettes, and they can protect against many kinds of antibiotics like beta-lactams, fluoroquinolones, and aminoglycosides. The plasmids can shuffle these genes around—rearranging them on the same plasmid or moving them to another one or even a chromosome—thanks to systems such as integrons, transposons, and ISCR-promoted gene mobilization. Most of these plasmids are conjugative, meaning they can transfer themselves from one bacterium to another, and that ability requires a lot more DNA than the smaller, non-conjugative ones, which is why conjugative plasmids tend to be much larger.
R-factor
R-factors, also known as resistance factors or resistance plasmids, are small, circular pieces of DNA that replicate on their own and carry genes that make bacteria resistant to antibiotics. They were first discovered in Japan in 1959, when scientists found that some strains of Shigella, a type of Gram-negative bacteria that causes dysentery, had developed resistance to multiple antibiotics. These resistance genes work by producing proteins that either modify the antibiotic or pump it out of the bacterium. Unlike mutations that block the antibiotic from entering or change the target protein, R-factors contain up to ten such genes and can spread quickly between bacteria using structures called pili. R-factors contribute significantly to the growing crisis of antibiotic resistance because they transfer these genes easily, though the R-factor itself cannot be passed on without transferring the whole plasmid.
Structure of Resistance Plasmids
The R-factor, a type of resistance plasmid, is a circular piece of DNA roughly 80 to 95 kilobases in length and closely related to the F factor. It contains most of the genes responsible for resistance transfer, including the R-RTF genes, and shares many similarities with the F factor, though it also has a fin 0 gene that blocks the transfer operon. The number and size of drug resistance genes in each R factor can vary. The RTF region is larger than the R determinant, and an IS 1 element sits between them, splitting the two sections before they come together into one unit. This IS 1 component helps make it easier for R determinants to move between different R-RTF units.
Transmission
Bacteria that carry F-factors, known as F+ bacteria, can share genetic material through a process called conjugation. They extend a sex pilus to reach another bacterium, draw it close, and form a mating bridge, allowing the transfer of plasmids between them. This method lets genes, including those for antibiotic resistance, spread easily among bacterial populations. Since many F+ bacteria also carry R-factors, resistance can move quickly. The gene responsible for this transfer is called RTF. Though transformation and transduction are other ways resistance spreads, conjugation remains the most common.
Enterobacteriaceae
Enterobacteriaceae is a family of Gram-negative bacteria that are rod-shaped and commonly found in both the environment and clinical settings. These bacteria are heavily influenced by antibiotic use in agriculture and medicine. Scientists can identify 28 different types of plasmids in this group using a method called PCR-based replicon typing. Some of the most frequently reported plasmids, like IncF, IncI, IncA/C, IncL, IncN, and IncH, carry many different resistance genes. Among these bacteria, species such as Escherichia coli and Klebsiella pneumoniae are especially concerning because they pose serious threats in both hospital and community infections due to plasmid-mediated resistance.
Beta-lactam resistance
Beta-lactamases are enzymes that break down beta-lactam antibiotics, making bacteria resistant to them. These enzymes are commonly found in Streptomyces, and when scientists discovered similar versions in both harmful and harmless bacteria, they realized they belong to a larger group called the "beta-lactamase superfamily." Researchers think these enzymes might have two roles — helping with normal cellular functions and providing resistance to antibiotics. In bacteria like those in the Enterobacteriaceae family, both narrow-spectrum and extended-spectrum beta-lactamases are often carried on plasmids, which can contain multiple genes that destroy a wide range of beta-lactam drugs.
Extended spectrum beta-lactamases (ESBL)
ESBL enzymes are capable of breaking down nearly all beta-lactam antibiotics, including cephalosporins, with the exception of carbapenems. The first ESBLs observed in clinical settings were mutated forms of older, narrower-spectrum beta-lactamases such as TEM and SHV. These enzymes also spread beyond the Enterobacteriaceae family, moving into new bacterial species. Because the plasmids carrying ESBL genes often include resistance to other types of antibiotics as well, strains that produce ESBLs are frequently resistant to many non-beta-lactam drugs, leaving clinicians with very few treatment options.
-
Read this chapter
Overview
Emerging infectious diseases (EIDs) are infections appearing newly or spreading quickly due to environmental shifts, antimicrobial resistance, and human-animal contact. Since at least 1940, these diseases have been on the rise, with each decade showing more events linked to wildlife zoonoses driven mainly by human activity and biodiversity loss. EIDs make up at least 12% of all human pathogens and can come from newly discovered microbes like novel coronaviruses or HIV, or from known ones such as new strains of influenza. Some emerge when existing diseases spread to new regions—like West Nile fever—or reappear after periods of decline, such as tuberculosis or measles. Hospital-acquired infections, including methicillin-resistant Staphylococcus aureus, are also becoming more common and dangerous due to antibiotic resistance. Many EIDs begin in animals, often with rare cross-species transmission, like most emergent viruses, while others, such as hepatitis C, may have been circulating undetected in species for years.
History of the concept of emerging infectious diseases
The concept of emerging infectious diseases developed over time, with early thoughts from the French doctor Charles Anglada in 1869, who wrote about extinct and new diseases without distinguishing between infectious and other illnesses. Later, Charles Nicolle expanded on this in his 1930 and 1933 books, asking whether infectious diseases have always existed or emerged over time. The term "emerging disease" appeared in scientific writing by the 1960s, with David Sencer defining them in 1971 as infectious diseases currently becoming public health problems, including both new and re-emerging ones. By the late 1980s, the AIDS epidemic brought renewed attention, leading to conferences like the 1989 NIH event where Stephen S. Morse highlighted that most emergent viruses are zoonotic and linked to human behavior increasing contact with animal hosts.
Climate change and environmental drivers
Climate change is driving the rise of new infectious diseases by altering ecosystems and human-animal interactions. Rising temperatures and changing rainfall patterns are expanding disease-carrying insects like mosquitoes and ticks into new regions, spreading dengue, malaria, Lyme disease, and West Nile virus to areas where they were once rare. Deforestation and habitat destruction are pushing wildlife closer to humans, increasing zoonotic disease transmission. Reduced biodiversity often leads to higher infection rates as the balance that controls pathogens is disrupted. Extreme weather events like floods, droughts, and heatwaves worsen these issues by damaging infrastructure, forcing population displacement, and weakening sanitation systems, particularly in poor communities. This complex environmental-health relationship is addressed through the One Health approach, which examines all connections together to better understand and prevent emerging diseases.
Zoonotic diseases
Zoonotic diseases, which jump from animals to humans, are a major danger to people worldwide. These illnesses, carried by viruses and other pathogens, make up around three-quarters of new infectious diseases we see emerging. Events like climate change and closer contact with wildlife have made it easier for these diseases to spread, leading to outbreaks such as Zika, Ebola, and COVID-19. To protect ourselves, we need to understand how these diseases move from animals to people, keep track of wildlife trade, and watch for early signs of trouble. One helpful method is monitoring wastewater, which can give us early warnings about new diseases before they spread widely.
Methicillin-resistant Staphylococcus aureus
Methicillin-resistant Staphylococcus aureus, or MRSA, came from a common bacterium called methicillin-susceptible Staphylococcus aureus, or MSSA. Most people carry S. aureus without getting sick, but when MSSA acquired the mecA gene in the 1960s, it became dangerous. That change made it resistant to methicillin and led to serious infections in hospitals and communities. Community-acquired MRSA is now seen in healthy people like athletes and schoolchildren. Scientists believe MSSA gained its resistance through horizontal gene transfer, spreading quickly among bacteria. Once in hospitals, MRSA picked up more resistance genes from other antibiotic-exposed bacteria, making it nearly impossible to treat. Because most antibiotics don’t work on MRSA, doctors must rely on alternative treatments and prevention methods.
-
Read this chapter
Overview
Whipple's disease is a rare condition caused by the bacterium Tropheryma whipplei, first described in 1907 by George Hoyt Whipple. Though it’s often seen as a gastrointestinal disorder, the illness can affect many parts of the body, including the heart, brain, joints, and skin. Common symptoms include weight loss, diarrhea, joint pain, and arthritis, though about 15% of patients don’t show the typical signs. The disease is much more common in men, with 87% of diagnosed cases being male. If caught and treated with long-term antibiotics, it can usually be cured, but without proper diagnosis or treatment, it can be fatal.
Signs and symptoms
People with Whipple's disease often start with diarrhea, belly pain, weight loss, and joint aches—sometimes years before digestive issues appear. The joint pains, called migratory nondeforming arthritis, usually hit large joints but don't damage them. A small number also have fever and chills. As the illness progresses, problems with nutrient absorption cause wasting and swollen lymph nodes in the abdomen. Severe cases may bring neurological symptoms like dementia, memory loss, confusion, or changes in consciousness. Eye movements can be affected, and some people develop oculomasticatory myorhythmia, a rapid muscle movement around the face. Headaches, seizures, and unsteady walking are also possible. Skin changes happen in about half the patients, including darkening and nodules. Eye issues like uveitis may cause pain and vision loss. Heart problems such as endocarditis, with breathlessness and leg swelling, have been seen even in people without other symptoms. Around 10 to 40 percent of those affected experience brain-related complications.
Pathogenesis
T. whipplei belongs to a group of bacteria related to the Mycobacterium avium complex, which helps explain why Whipple's disease shares features with illnesses caused by MAC bacteria. The condition tends to affect farmers and others who work with soil and animals, pointing to infection coming from these environments. People most at risk are those whose bodies struggle to break down pathogens inside cells, especially within macrophages. Research suggests that problems with T-lymphocytes, particularly the TH1 type, play a key role in making someone more likely to get sick. In those prone to the disease, cells expressing CD11b—also called integrin alpha—are lower than normal. This protein is essential for activating macrophages to destroy ingested T. whipplei bacteria.
Diagnosis
Whipple’s disease presents with a range of symptoms including diarrhea, weight loss, joint pain, and neurological issues, often starting with chronic arthritis before the intestinal problems become clear. Diagnosis relies on tissue samples taken during endoscopy, where doctors look for foamy macrophages that test positive with a special stain called PAS, and which contain Gram-positive bacilli. These findings are confirmed through immunohistochemical staining or PCR tests, especially when done on fluids like cerebrospinal fluid or heart valve tissue. While PCR can detect the bacteria in saliva, stool, or other samples, it's not definitive on its own since healthy people may carry the organism without showing signs of illness.
Treatment
Treatment for Whipple’s disease has historically involved penicillin, ampicillin, tetracycline, or co-trimoxazole over a period of one to two years. Studies showed that any course shorter than a year resulted in a relapse rate of roughly 40%. By 2007, experts were recommending a longer regimen of doxycycline combined with hydroxychloroquine, lasting between twelve and eighteen months. This combination works by raising the pH inside macrophages, which boosts the effectiveness of antibiotics against the bacteria hiding in acidic vacuoles. For patients experiencing neurological symptoms, sulfonamides like sulfadiazine or sulfamethoxazole might be added to the treatment plan.
Epidemiology
Whipple’s disease is incredibly rare, with only about one new case per million people each year. Most patients are male, with studies showing roughly two to three males affected for every female. In the United States and a few other countries, it's more common among Caucasians, which may point to a genetic factor. The bacterium T. whipplei lives in many people’s guts without causing harm, but something weakens the immune system in those who get sick. That defect seems specific to this bug, since patients don’t face a higher risk of other infections. Most people are diagnosed around age forty-nine, though in Germany, the average age of diagnosis has been going up since the 1960s.
History
In 1907, Whipple described the disease in a paper in the Bulletin of Johns Hopkins Hospital. The patient was a 36-year-old medical missionary, and Whipple referred to the illness as "intestinal lipodystrophy." For years, it was thought to be infectious, but the actual organism wasn’t fully identified until 1992. Then, in 2003, doctors from Johns Hopkins Hospital worked with the French microbiologist Didier Raoult. Using new diagnostic methods, they examined stored tissue samples from Whipple’s original patient and found T. whipplei in those tissues.
Read
Free to download, keep and share. For general information only — not professional medical, legal or financial advice. Please consult a qualified professional.