One of the best parts of Microcosm is its discussion of antibiotics and how E. coli and other bacteria can quickly evolve to outwit them. Zimmer explains how some bacteria can even enter a state of hyper-mutation as a result of antimicrobial or antibiotic attack: when E. coli needs it most, it starts messing with its genetic code in order mutate, and evade the attack, faster.

It’s scary material, considering that widespread antibiotic use got started during World War II with penicillin and now, several generations of antibiotics later, it seems like we’re still losing the war against bacterial resistance. By as early as 1948, Zimmer notes, “doctors reported that penicillin was beginning to fail in their Staphylococcus-infected patients.” Yet:

These disturbing discoveries did nothing to halt the rise of antibiotics. Today the world consumes more than ten thousand tons of antibiotics a year. Some of those drugs save lives, but a lot of them are wasted. Two-thirds of all the prescriptions that doctors hand out for antibiotics are useless. Antibiotics can’t kill viruses, for instance. Many farmers today practically drown their animals with antibiotics because the drugs somehow make the animals grow bigger. But the cost of antibiotics is greater than the profit from the extra meat.

It would have been wonderful if Zimmer had decided to include a little more about where those numbers come from and what they mean. Does useless include prescriptions that are not used to completion or are used for a purpose other than what they were prescribed for? More importantly, however, Zimmer does an excellent job describing the process by which bacteria become resistant.

His discussion of Shigella infections in Japan after World War II is fascinating. It was in the late forties that Japanese doctors started to encounter bacteria that were resistant to not just a single antibiotic, but to all of them. It turned out that the Shigella bacteria were able to trade genes through Lederberg’s bacterial sex and through viral infections of the bacteria themselves. These and other strategies are collectively known as horizontal gene transfer, which, Zimmer writes, “allows genes to leapfrog from microbe to microbe across staggering distances. In the jungles of French Guinea, scientists have found antibiotic-resistant E. coli in the guts of Wayampi Indians, who have never taken the drugs.”

Some of the most interesting questions Zimmer raises in the book come from such discussions of the “murky struggles” between parasite and host, and the role of bacteria and viruses in human evolution:

Most viruses simply invade our cells, which produce new viruses that move on to the next host. But some viruses inset their genetic material in a cell’s genome. If they manage to infect a sperm or an egg, these viruses will be passed down from one generation of humans to the next. Over many generations, mutations cause the viruses to lose their ability to escape their host cells. Many lose most of their genes. What remains are instructions for making copies of their DNA and pasting that DNA back on their host’s genome. These genomic parasites now make up about 8 percent of the human genome. Recent research suggests that some of them have been harnessed by their hosts. A number of essential human genes, which help build things as different as antibodies and placentas, evolved from virus genes. Without our resident viruses we would not be able to survive. Once again, what is true for E. coli is true for the elephant: Where do our own viruses stop, and where do we begin?

With descriptions like that, Microcosm excels at making the science of E.coli accessible for lay audiences. Reaching far beyond the food scares of recent years, it is a story of discovery that illuminates a microscopic and alien world and explains how it has helped guide the course of human history. Anybody that picks up a copy will find that Zimmer has produced a book not just about E. coli, but about microbiology and evolution itself.

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