Chapter 4
The Rise of Pathogens: A Delicate Balance
Not all microbes are beneficial. Pathogens are microbes that make us ill, bringing fevers, chills, and pains that can sometimes kill. For 70 years, we've aggressively fought pathogenic bacteria with antibiotics, saving millions of lives but facing the constant challenge of bacterial mutation and resistance.
Consider Rocky Mountain spotted fever, a tick-borne rickettsial infection. An eleven-year-old boy hospitalized with this disease had his body covered in purple spots, thrashing deliriously in his hospital bed, hallucinating and shouting obscenities while his conservative Baptist parents cowered in the corner. The bacteria had multiplied within his blood vessel cells, causing inflammation that explained both his rash and encephalitis. Without immediate tetracycline treatment, this disease kills up to 30% of victims.
Yet pathogens aren't inherently evil-they're predators pursuing their own survival. Their damage to hosts is sometimes accidental, but often serves their reproductive purposes. Tuberculosis bacteria make people cough to spread themselves; rabies virus attacks brain regions controlling aggressive biting behavior. With over 1,400 recognized human pathogens, they range from high-grade killers to low-grade opportunists that mainly affect compromised individuals.
For most of human prehistory, our hunter-gatherer ancestors lived in small isolated groups of 30-60 individuals, making epidemic diseases impossible. Pathogens like tuberculosis and chickenpox developed latency strategies to survive in small populations-lying dormant for decades before reactivating (like shingles emerging from childhood chickenpox).
When agriculture began 10,000 years ago, growing populations and cities created perfect conditions for epidemic diseases. Measles, the most infectious disease known with 95% infection rates, requires contiguous populations of 500,000 to persist-impossible before cities developed. The rise of cities brought additional problems like plague-carrying rats attracted to stored food.
The Industrial Revolution further accelerated disease spread through crowding and poor sanitation, making tuberculosis America's leading killer by 1900. Only in the late nineteenth and early twentieth centuries did advances in sanitation, vaccines, and eventually antibiotics begin turning the tide against these pathogens. But this victory came with hidden costs we're only now beginning to understand.
Chapter 5
The Wonder Drugs: A Double-Edged Sword
In spring 1980, Dr. Blaser returned to Atlanta after working in Bangladesh and India. Despite feeling feverish and achy, he initially dismissed it as jet lag or flu. When symptoms persisted with fever reaching 104F, he became too weak to button his shirt. Driving to the doctor through streets lined with blooming magnolias, he feared he might die at thirty-one from what he suspected was typhoid fever contracted during his travels.
At the hospital, he recommended treatment with co-trimoxazole rather than ampicillin, which many typhoid strains had become resistant to. Blood cultures confirmed Salmonella paratyphi A infection. After three weeks-one in hospital and two recovering-he was well again. Later, a colleague explained his infection likely came from a watermelon in Mumbai, where farmers inject river water into melons to increase their weight.
Before antibiotics, bacterial infections were often deadly. During the American Civil War, more soldiers died from typhoid and dysentery than bullets. The Spanish Flu of 1918-1919 killed 20-40 million people, many from bacterial pneumonia complications. Despite advances in germ theory by pioneers like Pasteur, Lister, and Koch, effective treatments remained elusive.
Alexander Fleming's accidental 1928 discovery changed everything. Returning from vacation, he noticed a blue-green mold (Penicillium notatum) on a forgotten petri dish had created a bacteria-free zone around itself. Fleming isolated the antibacterial substance and named it penicillin, though he couldn't produce it in useful quantities.
During World War II, Howard Florey and Ernst Chain revived Fleming's work, taking it to America where pharmaceutical companies scaled up production. The search for productive penicillin strains led to a nationwide collection effort, with "Moldy Mary" scouring Peoria markets for moldy samples. A housewife's moldy cantaloupe yielded a strain producing 250 units per milliliter, and its mutant eventually produced 50,000 units. By June 1944, 100 billion units were being produced monthly-just in time for D-Day.
Antibiotics transformed medicine, making formerly lethal diseases curable and enabling advanced surgical procedures and cancer treatments. But their very success led to complacency and overuse, setting the stage for today's crisis.
Chapter 6
The Overuse of Antibiotics: An Invisible Epidemic
Despite their remarkable effectiveness and apparent safety, antibiotics began being prescribed for increasingly minor conditions. The most problematic area became upper respiratory tract infections-conditions that affect children repeatedly in early life and circulate constantly through our social networks. The critical issue: over 80% of these infections are caused by viruses, which antibiotics cannot treat.
Doctors face an impossible dilemma when treating children with respiratory infections. Without clear diagnostic tools to distinguish viral from bacterial causes, physicians err on the side of caution. They fear rare but serious complications like pneumonia or mastoiditis, and especially rheumatic fever-a devastating inflammatory disease that can attack a child's heart, joints, skin and brain after untreated strep infections.
The problem compounds when healthy bacterial carriers get viral infections. A child colonized with Group A strep who catches a cold might test positive for strep, leading to unnecessary antibiotics. Since most children recover quickly regardless of treatment, parents mistakenly attribute improvement to the medication rather than natural healing.
The scale of antibiotic use has grown from treating 64 pneumonia patients in 1945 to 258 million prescriptions in the United States alone by 2010-about 833 prescriptions per thousand people. Children under two receive the highest rate: 1,365 courses per 1,000 babies, meaning the average American child takes nearly 3 courses of antibiotics before age two, another 8 courses by age ten, and roughly 17 courses before turning twenty.
This massive exposure has two immediate consequences. First, resistance: when we take antibiotics like amoxicillin, they don't just target pathogens but kill susceptible bacteria throughout the body-a carpet bombing when a precise strike is needed. This creates perfect conditions for resistant bacteria to flourish without competition.
Second, pharmaceutical companies are no longer developing new antibiotics to keep pace with resistance. The economics don't work-companies prefer drugs that millions will take for years (like those for diabetes or high blood pressure) rather than antibiotics used by relatively few people for short periods.
But there's a third, more insidious consequence: the disruption of our essential microbiome, potentially contributing to the modern plagues we're witnessing today.
Chapter 7
The Modern Farmer: Agricultural Antibiotics
Our pastoral image of cattle grazing in open fields has been replaced by industrial operations where animals are packed into small spaces. Most antibiotics in the United States go not to humans but to these massive feedlots for cattle, swine, and poultry. Agricultural science focuses on maximizing meat production through optimized feed efficiency, with antibiotics playing a central role in fattening animals faster.
Factory farms administer subtherapeutic doses of antibiotics not primarily to prevent disease in crowded conditions, but to enhance "feed efficiency"-helping animals gain more weight more quickly. This practice dates to the 1940s when pharmaceutical manufacturers discovered antibiotics' growth-promoting effects. A 1963 study revealed that conventionally raised chickens given antibiotics grew bigger than untreated controls, but germ-free chickens showed no difference-proving that microbes are essential for the growth-promoting effect.
Today, 70-80% of all antibiotics sold in the United States are used for fattening farm animals, with producers buying nearly 30 million pounds in 2011. The practice creates serious public health concerns. In 2013, Consumer Reports found that most bacterial samples from pork were resistant to at least one antibiotic, with some containing MRSA. Government testing in 2011 revealed that over half of ground turkey, pork chops, and ground beef samples contained antibiotic-resistant bacteria.
While Sweden banned growth-promoting antibiotics in 1986 and the European Union followed in 1999, American producers continue the practice, arguing there's no proof that resistant microbes from animals infect humans. However, evidence going back thirty years shows identical resistant organisms in sick people and animals fed antibiotics. A 2013 Danish study using genome sequencing definitively linked MRSA infections in farmers to the same strains infecting their animals.
Beyond resistant bacteria, the antibiotics themselves reach humans through food. Though the FDA establishes "maximum residue limits," a child drinking two cups of milk daily might consume 50 micrograms of tetracycline every day. Antibiotics also contaminate water supplies, with a 2009 study finding antibiotic-resistant bacteria and genes in all source waters, treatment plants, and tap water.
The most concerning parallel is between agricultural growth promotion and human health-if antibiotics fatten farm animals by changing their development, might we be inadvertently doing the same to our children when treating their illnesses?
Chapter 8
Mother and Child: The Critical First Transfer
Birth practices have changed dramatically over the past 150 years, making childbirth safer but introducing silent hazards we're just beginning to understand. High C-section rates and antibiotic overuse are altering the microbial species mothers pass to newborns.
Throughout the animal kingdom, mothers transfer microbes to their young during birth. In humans, as pregnancy progresses, lactobacilli flourish in the vaginal canal, preparing for birth. When labor begins and water breaks, these beneficial bacteria colonize the mother's skin. As the baby passes through the birth canal, its skin absorbs these microbes. The baby's first suck contains lactobacilli, perfectly timed to digest the lactose in mother's milk.
This choreographed transfer ensures founding bacteria in the newborn's gut include species that can digest milk and inhibit dangerous competitors. These first microbes activate genes in the baby and build niches for future populations, stimulating gut development and immunity. By age three, each child acquires their own unique foundation of microbes during this critical period that lays the groundwork for all biological processes throughout life-unless something disrupts this natural progression.
C-section delivery disrupts this natural microbial handoff. Instead of acquiring beneficial lactobacilli during vaginal birth, babies are surgically extracted through an abdominal incision. Though invented in Roman times to save babies when mothers inevitably died, today's C-sections are very safe and increasingly common. U.S. rates increased from under 20% in 1996 to 33% in 2011, with dramatic global variations-from 80% in Rome to just 13% in the Netherlands.
The biological cost affects the baby: studies show C-section newborns harbor skin bacteria like Staphylococcus rather than vaginal Lactobacillus. Though microbiome differences diminish over time, those critical founding populations may provide essential developmental signals during the newborn's rapid development.
Antibiotics given during pregnancy and birth present another threat. About 40% of American women receive antibiotics during delivery-all C-section mothers get preventive doses, and those testing positive for Group B strep (25-33% of pregnant women) receive intravenous penicillin during labor. Though intended to prevent rare but serious infections, these broad-spectrum antibiotics kill beneficial bacteria and select for resistant ones just before the critical intergenerational microbial transfer.
What happens when we disrupt this ancient pattern of microbial inheritance? The consequences may be far-reaching and long-lasting.
Chapter 9
The Disappearing Guardian: H. pylori's Story
The overuse of antibiotics in humans and animals, along with changing birth practices, inevitably affects our microbial inhabitants. Over fifteen years ago, Dr. Blaser began investigating whether the loss of our ancient, functionally conserved microbes has led to modern plagues like obesity, juvenile diabetes, and asthma. The ancient stomach bacterium Helicobacter pylori has been his guide, demonstrating the concept of amphibiosis-relationships that can be either symbiotic or parasitic depending on context.
H. pylori are curved bacteria that live exclusively in the human stomach's protective mucus layer. With deep evolutionary roots, these bacteria have been with humans for at least 100,000 years, likely since Homo sapiens emerged 200,000 years ago in Africa. Until recently, H. pylori colonized virtually all children early in life, persisting throughout their lifetime.
In the 19th century, pathologists observed curved bacteria in everyone's stomach, but these organisms couldn't be cultured and were eventually forgotten. Medical dogma shifted to believe the stomach was sterile due to its battery-like acidity. In 1979, Australian pathologist Robin Warren rediscovered these bacteria and noted their association with gastritis (stomach inflammation). Barry Marshall joined Warren, and in 1982 they successfully cultured these organisms. To prove causation, Marshall famously drank a culture of H. pylori in 1984, developing gastritis that resolved spontaneously.
After developing the first accurate blood test for H. pylori in 1987, Dr. Blaser's team began investigating why only some carriers developed ulcers. They identified a protein they named cagA that was consistently present in strains from ulcer patients but only in about 60% of non-ulcer carriers. These virulent strains contain gene clusters that not only produce interactive proteins like CagA but also form injection systems to deliver these materials directly into stomach wall cells, increasing inflammation.
By 1994, the World Health Organization declared H. pylori a Class 1 carcinogen. This led to the medical consensus that "the only good Helicobacter pylori is a dead one," with doctors worldwide seeking to eliminate it whenever found.
But Dr. Blaser realized H. pylori was becoming extinct in developed countries. While nearly all adults in Africa, Asia, and Latin America still carry H. pylori, fewer than 6% of American children born after 1995 have it. This disappearance follows socioeconomic lines worldwide, with wealthier populations losing the bacteria faster.
Three major factors drive this extinction: improved sanitation (especially clean water), smaller family sizes, and widespread antibiotic use. Each course of antibiotics eliminates H. pylori in 20-50% of patients, creating a cumulative effect across generations. With Americans averaging seventeen antibiotic courses by age twenty, and mothers without H. pylori rarely transmitting it to children, we're experiencing a multigenerational decline in this ancient stomach resident.
The fundamental question became: what is normal? Pathologists see a stomach filled with lymphocytes and macrophages as "chronic gastritis," but ecologists might view this as the natural physiological response to indigenous organisms. Our relationship with ancient microbes like H. pylori involves constant adaptation and equilibrium-a dynamic communication system regulating inflammation in specific locations.
With H. pylori's disappearance, this ancient equilibrium has been disrupted, creating a dance without a partner. The effects aren't just immediate or local but lifelong, with new diseases rising as a consequence.
Chapter 10
Modern Plagues: The Hidden Connection
The increasing prevalence of autoimmune and metabolic diseases represents a disturbing trend in modern society, with Type 1 diabetes serving as a prime example. Kathy developed Type 1 diabetes at thirteen, initially managing with diet alone before requiring insulin injections. Despite her determination to live fully-graduating college, becoming a social worker, marrying, and having children-the disease gradually took its toll. She lost sensation in her feet, her hands contorted, and her daughter developed diabetes at nine. After kidney failure and a heart attack, Kathy died just before her fiftieth birthday.
Type 1 diabetes rates are doubling every twenty years across the developed world, with children developing the disease at increasingly younger ages-now averaging around six years old compared to nine when Kathy was diagnosed. Some children develop it as young as two or three, meaning their insulin-producing cells are disappearing before their second birthdays.
Working with medical student Alexandra Livanos, Dr. Blaser studied how early-life antibiotics affect NOD mice that spontaneously develop Type 1 diabetes. Their preliminary results showed that pulsed antibiotic treatment (PAT) accelerated disease onset, particularly in males. Even before diabetes developed, their pancreases showed severe inflammation with immune cells attacking insulin-producing islets. Intestinal immune cells were altered by antibiotics before pancreatic damage appeared, suggesting abnormal gut interactions precede pancreatic destruction.
Celiac disease shows similar patterns. Swedish research revealed people with celiac disease were 40% more likely to have received antibiotics in preceding months compared to healthy controls. The risk increased with more courses, and metronidazole showed the strongest association-doubling celiac risk. In another study examining 136,000 patients, those with H. pylori in their stomachs had significantly lower rates of celiac disease (4.4% versus 8.8%).
Inflammatory bowel disease (IBD) is increasing worldwide as industrialization spreads. Danish researchers tracked over 577,000 children for six years and found those who developed early IBD were 84% more likely to have received antibiotics. Children who took antibiotics had triple the risk of developing Crohn's disease, with each course increasing risk by 18%. Those receiving seven or more courses faced seven times greater risk.
Hay fever and eczema have risen dramatically alongside asthma, with many children experiencing all three conditions. Nut allergies have exploded from extremely rare to affecting up to one in fifty children, with peanut allergies more than tripling between 1997 and 2008.
Even autism, which has soared from being uncommon when first described in 1943 to affecting one in eighty-eight children today, may connect to gut microbes involved in early brain development. The gut contains over 100 million neurons that communicate directly with the brain via the vagus nerve. These neurons interact constantly with gut microbes, which produce chemicals the developing brain needs, including gangliosides. Gut cells also produce 80% of the body's serotonin, which regulates learning, mood and sleep.
The disruption of our microbiome may be depleting our defensive reserves against multiple modern diseases, compounding across generations. We're conducting an unintended experiment on ourselves, with consequences we're only beginning to understand.
Chapter 11
Antibiotic Winter: The Coming Crisis
The growing crisis of antibiotic resistance threatens a future Dr. Blaser calls "antibiotic winter"-analogous to Rachel Carson's Silent Spring warning about pesticides and birds. Peggy Lillis, a 56-year-old kindergarten teacher, died in April 2010 just weeks after taking clindamycin for a minor dental procedure. The antibiotic wiped out her protective gut bacteria, allowing Clostridium difficile to flourish. This normally harmless bacterium produced toxins that made her colon porous, leading to sepsis. Despite emergency surgery to remove most of her colon, she died less than two weeks after her dental work.
C. diff infections were once primarily hospital-acquired, where antibiotics are heavily used and spores easily spread. While better infection control in the 1990s reduced cases, the last decade has seen more severe infections with higher mortality. Analysis shows strains have evolved to produce more toxin. Even more alarming, C. diff has escaped hospitals into the community, infecting people like Peggy who had no hospital exposure.
The CDC's landmark 2013 report ranked eighteen drug-resistant bacteria by threat level, with CRE (carbapenem-resistant enterobacteriaceae) at the top as "urgent." These deadly microbes resist virtually all antibiotics and can spread resistance genes to other bacteria. They've been identified in healthcare facilities across 44 states. CDC Director Tom Frieden warned that "the medicine cabinet may be empty for patients with life-threatening infections" in the near future.
Experiments from the 1950s showed that mice given antibiotics became dramatically more susceptible to Salmonella infection-requiring only three bacteria to cause infection compared to 100,000 in untreated mice. This thirty-thousand-fold difference persisted even weeks after antibiotic exposure. The phenomenon applies to humans too: during Chicago's massive 1985 Salmonella outbreak affecting 160,000 people, those who had taken antibiotics in the month prior were 5.5 times more likely to become ill than others who drank the contaminated milk.
Beyond shifting bacterial populations, Dr. Blaser worries about complete extinction of rare "contingency species"-microbes present in small numbers that could be entirely wiped out by antibiotics. Like finding Waldo in a crowd, these rare species may go unnoticed when eliminated. Even small bacterial populations can explode into billions when conditions favor them, such as encountering a food component only they can digest. Their loss represents declining microbial biodiversity, making us more vulnerable to pathogens.
Our world faces unprecedented vulnerability to epidemics. With 7 billion people increasing by 80 million annually, and many with compromised internal ecosystems from antibiotic exposure, we're setting the stage for potentially catastrophic plagues. Modern travel networks can spread pathogens globally within days. The Great Influenza of 1918-19 killed tens of millions without commercial air travel; today we're far more connected and vulnerable.
Chapter 12
Restoring Balance: Solutions for a Microbial Future
We need antibiotics for serious infections, but we must curb our excessive appetite for these powerful drugs. This is the most achievable step we can take to slow the daily damage to our microbial diversity.
Each of us can take personal responsibility with antibiotics: wait a few days before taking medication for persistent coughs or children's colds; resist pressuring physicians for quick fixes; question dentists about antibiotic necessity; and stop overusing sanitizers-good old soap and water works fine. Of course, truly ill children with high fevers, breathing difficulties, or severe symptoms need immediate medical attention and antibiotics when necessary.
Doctors face a conundrum: antibiotics are vital yet prescribed excessively-over 41 million courses annually to U.S. children. Healthcare providers need better training to think twice before prescribing, carefully weighing each situation. Paradoxically, pediatricians making crucial health decisions are among the lowest-paid physicians. They should be paid sufficiently to methodically evaluate children and discuss diagnoses with parents.
France provides an excellent model for reducing antibiotic use. After having Europe's highest rate in 2001, their "Antibiotics Are Not Automatic" campaign targeted both patients and healthcare providers, focusing on reducing prescriptions for children with viral respiratory infections. By 2007, prescription rates had declined 26% overall and 36% for children under three.
The pharmaceutical industry's focus on broad-spectrum antibiotics that kill many microbes needs overhauling. While convenient for immediate treatment, these drugs cause greater collateral damage to beneficial bacteria. We should return to Paul Ehrlich's century-old approach of developing narrow-spectrum agents targeting specific pathogens.
New diagnostic tests are being developed that can better distinguish between viral and bacterial infections by identifying specific agents. Another promising approach uses the host's immune responses as indicators of which organism is causing the problem. Though these technologies are in early stages, their widespread implementation is feasible.
Women should question the necessity of elective C-sections and only undergo them when medically required. For cases where C-sections are necessary, Dr. Blaser's wife Gloria is studying the "gauze-in-the-vagina technique" in Puerto Rico. This simple procedure collects bacteria-laden secretions from the mother's vagina and gently swabs the newborn's skin and mouth post-birth, helping to transfer microbes the baby would miss during a surgical delivery.
Fecal microbiota transplantation (FMT) has shown remarkable success in treating recurrent C. diff infections. Despite its effectiveness, the FDA has reasonably imposed regulatory hurdles to ensure safety, especially important when transferring biological materials between people. Using pure cultures of probiotic bacteria could potentially eliminate these human-to-human transmission risks.
Just as the internal combustion engine transformed human life with both benefits and unforeseen consequences like global warming, our manipulation of microecology through antibiotics and C-sections has created similar unintended effects. These changes to our resident microbes have occurred rapidly-only about a century, with acceleration in the past 60-70 years.
We stand at a crossroads where the practices endangering our children are core to modern healthcare. The consequences are already visible and worsening, but solutions exist. By combining approaches like curtailing both C-sections and antibiotic use while replacing disappeared organisms, we can begin reversing these trends. For our children's future, we must implement these changes urgently.
