Food, Sex and Salmonella. David Waltner-Toews

the United States in contaminated candy. Among the many we might reflect upon, the story of Salmonella enteritidis may be one of the more instructive.

      Chickens and turkeys often carry a few Salmonella in their intestines or on their feathers, without any apparent ill effects. Tens of millions of people have gotten sick from similarly few Salmonella over the past few decades, and many have died. We are currently on the slowly declining tail (we hope) of a global pandemic of salmonellosis, mostly from chickens and mostly S.enteritidis. But bacteria are, from an evolutionary point of view, considerably more “fit” than the rest of us, and the emergence of S. enteritidis furnishes a cautionary tale.

      In the early twentieth century, two serologically related Salmonellas—S. gallinarum, which causes diarrhea in chicks, and S. pullorum, or fowl typhoid, were quite common in poultry flocks in Europe and North America. Veterinarians noticed two important things about these organisms: they were adapted to domestic chickens and waterfowl, and they made the birds (but not people) sick. The first characteristic made the disease vulnerable to a “test and slaughter” method of eradication—a kind of mass-slaughter/napalm operation that many animal disease control people seem to find attractive (someone should do a psychological study on that); the second characteristic was strong motivation to carry out such a program. The eradication of fowl typhoid has been a success story; the disease is rare in any country that boasts a “modern” poultry industry.

      About the same time as this Salmonella was eliminated from poultry, another Salmonella—S. enteritidis—wandered over from its natural home in rodents and took up residence in the vacated ecological niche. Not many disease specialists know much about ecology, so this shift in bacterial ecology was not widely investigated. The notion that various species of all types and sizes in the world are interconnected, and that ecological niches are not really vacated but just filled with other species, makes disease treatment and control seem, well, complicated.

      In any case, the vets didn’t worry too much about it, since enteritidis doesn’t make chickens sick. It does make people sick, however, but veterinarians and physicians have a long history of not talking much to each other. By the late 1980s, there was a global pandemic—in people, not chickens. Enteritidis was even more clever than scientists imagined, since it lived inside the ovaries of the birds laying the eggs, and they got it from their closely guarded and very valuable parents, the so-called breeder flocks. These flocks are the source of most of the world’s commercial chickens. People didn’t even have to be dirty to get sick. All that hand washing and all those chemicals for naught! All those great genetics! How could a bacterium be so vile and anarchistic?

      In 1988, Edwina Currie, then a junior health minister in the British government, drew attention to a problem with S. enteritidis in eggs. After Edwina made her announcement, sales of eggs in the UK fell by 60 percent overnight, and many egg producers went out of business; Edwina herself was relieved of her job. By 1994, Edwina was back in the news, helping to launch a celebrity-chef cookbook called My Perfect Omelette and claiming that British eggs were now the safest in the world. That may well be, but the global pandemic of salmonellosis is not over yet, and the organisms keep coming up with new chemical-evading stratagems as fast as those chemicals can be devised.

      S. enteritidis continues to adapt. An epidemic in Canada and the United States of an unusual molecular strain, PT 30, was traced to raw whole almonds in 2000 and 2001. (The PT refers to “phage type”; phages are viruses that infect bacteria and can be used to trace them.) PT 30 is an uncommon strain in foodborne diseases, and almonds are an uncommon vehicle for infection. Investigators looked everywhere for an animal source, since Salmonella are not supposed to live out there in the wild without an animal host. They couldn’t find any animals near the nut farms. One of the researchers has suggested that the bacteria have been growing in the soil, which, because the almond growers have been growing trees at much higher densities than was once thought possible, is richer in nutrients than was once thought possible. If this supposition is true, then people have pushed the bacteria down new, interesting, and (for consumers) dangerous evolutionary paths.

      Most Salmonella do not travel first class, as the ones inside the eggs have. Usually, they hang around in the dust and feces in the chicken barn, cling to the outside of the eggshell, and only get into the eggs after the eggshells have been washed. A 2006 survey in Europe found that in some countries, such as the Czech Republic, Poland, and Spain, more than 70 percent of egg-laying flocks are infected with Salmonella. With the exception of the Nordic countries (which have all but eradicated the disease in animals), other industrialized countries have lower, but still substantial, levels of contamination. In washing the eggs, people remove not only the visible dirt but also the less visible protective layer that the hen has secreted over her baby’s shell. The invisible bacteria are left intact and ready to invade through the pores of the egg, which they do as the shell dries.

      Salmonella in cattle may move from the rural backwoods of intestinal living to adopt suburban lifestyles in lymph nodes. Even people can carry the organisms without being sick. Mary Malone, the infamous cook called Typhoid Mary, was one of many such people who have spread infections without themselves being sick. How we deal with such people (or animals) raises all the great questions of private rights versus public good that are at the heart of public health. Should people be quarantined? Cautioned? Charged with mischief?

      A few bacteria do not usually cause much of a problem. What brings the masses out into the streets, however, is stress. Crowding the chickens or pigs together, and piling them into trucks to go to the slaughterhouse, brings Salmonella into the bracing, rebellious air, infiltrating feathers, splotching skin, and multiplying and filling the earth. If animals are not contaminated before they get into the truck to go to slaughter, they probably are afterward. Various studies find significant degrees of contamination in retail meats in Canada, the United States, and Europe (with the exception of the Nordic countries). Even if the prevalence gets down to, say, 1 percent, you, as a consumer, don’t know which 1 percent that is.

      With all the scalds and disinfectants in modern packing plants, a lot of bacteria on the chickens do meet their end at the slaughterhouse. But with the crowds out full force, there are always a few million to spare, and bacteria love to multiply. Some of those millions get siphoned off into the meat by-products and from there get into the animal feeds and go back to the quiet life on the farm. The rest of them head off to the bright city lights, weddings, family reunions, papal visits, hospitals, and nursing homes.

      From the point of view of the bacteria, bigger is better; the more intensive and large scale the livestock operations, the more extensive and devastating the foodborne disease, as well as the ecological problems. Salmonella in the family cow no longer need to content themselves with recycling through the same boring small family but get a free ride across the country and around the world. The notion of bacteria coming through in the eggs really only becomes frightening when one considers that a few major companies supply all the source birds for the egg industry. Monocultures and world trade are tailor-made for bacterial survival: the economies of scale are the economics of pandemics.

      Another way to help the Salmonella along at the farm is to feed the animals antibiotics, which kill off the other neighborhood bacteria. The hardy and often drug-resistant Salmonella, never being ones to waste an opportunity, move into the homes we have cleaned out with our preemptive public safety measures. This tactic also works at home; you can sometimes lure a latent case of salmonellosis out of the closet by taking penicillin. Because of the massive amounts of antibiotics used in both people and animals, some people fear that drug-resistant Salmonella might take over the world. Drug-resistant bacteria, however, are adapted to live in a drug-filled environment, and if we cut back on our profligate antibiotic use, they would not give us problems.

      If the bacteria can almost count on a quiet home on the farm, opportunities to spread from animal to animal abound on the truck to market. Even more opportunities arise at slaughter, and they most certainly can look forward to sloppiness in the kitchen. The counter becomes contaminated with bacteria when the turkey is put down there for dressing. Those that accompany the bird into the oven usually get killed off, but a healthy population lurks on the counter and repopulates