Bacteria that are immune to several antibiotics are showing up in a broad range of foods on grocery store shelves, new studies show.

It’s a recipe for rising illness and deaths from food poisoning, according to data reported in Orlando, Fla., this week at the American Society for Microbiology meeting.

When virulent, the microbes can induce gut-wrenching poisoning. There also is a risk that, once bacteria mingle on the cut- ting board or in a diner’s gastrointestinal tract, even benign bacteria that happen to be resistant to drugs could share their resistance genes with more dangerous mi- crobes. Later, infections caused by the modified microbes might prove intractable.

Bacteria can develop drug resistance in the environment, in hospitals, and even within a person treated with antibiotics. However, animal agriculture is playing a disproportionately large role, says Burke A. Cunha, who heads the division of in- fectious diseases at WinthropUniversity Hospital in Mineola, N.Y.

“The volume of antibiotics used in ani- mal feeds equals or exceeds that used to treat infections in humans,” he notes in the April 28 LANCET. What’s more, he told SCIENCE NEWS, “many of the antibiotics that have been used to supplement ani- mal feeds are the very ones most likely to induce resistance.”

If livestock develop resistant bacteria (SN: 7/18/98, p. 39), the bugs can taint meat or foods exposed to the animals’ wastes, Cunha says.

Several reports in Orlando included accounts of such tainted foods. For exam- ple, Michael Teuber of the Swiss Federal Research Institute in Zurich isolated Ente- rococcus faecalis from salamis, which were fermented and made from raw meat. The normally harmless bacteria, which serve as an indicator of fecal contamination, were resistant to five common antibiotics: chloramphenicol, erythromycin, strepto- mycin, streptothricin, and kanamycin.

In lab tests, Teuber incubated E. fae- culis with other “not very closely related bugs,” such as lactococcus and Listeria. The salamis’ bacteria readily donated their resistance genes to the others, he reports. The enterococcus carried these genes on one of its two plasmids, which are circular strips of DNA that many bac- teria freely swap with each other.

When Teuber’s group examined single- serving-size salamis in the United States, it found no bacteria. The difference, Teuber says, is that these little salamis had been sterilized during production.

However, David D. Wagner and his col- leagues at the Food and Drug Administra- tion in Laurel, Md., identified enterococcus species, including E. faecalis, in brand- name retail cuts of raw meat from local su- permarkets. To rule out in-store tainting,

nella, 8 percent showed bacterial resist- ance to antibiotics, and the rate was highest in imports from developing na- tions. Some resisted as many as six differ- ent drugs. The antibiotic-resistant bacte-

Antibiotic resistance is coming to dinner they included only factory-packaged meat. Overall, the bacteria turned up in 67 per- cent of the chicken, 34 percent of’the turkey, and 66 percent of the beef. At least some of the microbes in each contaminat- ed sample proved resistant to multiple an- tibiotics, though not necessarily to the same drug combos.

The birds were resistant to more drugs than the beef. For example, 70 percent were immune to penicillin and 39 percent to streptomycin. Beef microbes were re- sistant to neither. However, bacteria from both poultry and beef showed high rates of resistance to feed-additive antibiotics such as tetracycline.

In response to this study, FDA has just launched a year-long trial to test meats weekly in Iowa. Wagner says it’s a pre- lude to a national monitoring program for drug resistance in meats.

Shaohua Zhao of FDA last year tested for antibiotic-resistant bacteria in US. im- ports of foods other than meat. Of the 187 samples contaminated with Salrno-

ria showed up primarily in fresh and frozen seafood, but there was one case in parsley and another in cheese.

The new reports “follow a theme that we saw through the ’90s-that [bacterial] resistance is not to one or two agents, but to four, five, and six,” notes Stuart B. Levy, director of the Center for Adapta- tion Genetics and Drug Resistance at Tufts University in Boston.

“We like to think that our food supply is perfectly safe, and I think it can be if we address [the resistance problem] more aggressively,” he says. “But that is going to take time and additional funds from the state and federal governments.”

Until then, Levy recommends that con- sumers assume a defensive approach by cooking foods to germ-killing tempera- tures, thoroughly washing all foods to be eaten raw, and meticulously cleaning all food-preparation surfaces after any con- tact with raw foods. -J Raloff

Designer surface proves deadly to bacteria Using a novel approach to microbe face kills even hard-to-attack, airborne

killing, a team of researchers has made a bacteria, such as those lofted during a new coating that could render counter- sneeze or delivered by an air duct. tops, computer keyboards, and even hos- The surface modification is not limited pita1 sheets permanently antiseptic. to glass, adds Klibanov. Researchers

Unlike most antibacterial treatments, could use the coating method to create which lose microbe-repelling power as permanent antiseptic coatings for door their active components leach out, the 7i; new surface coating has an enduring. ? h- built-in chemistry f& killing bacteria on E contact, says team member Kim Lewis, a ir microbiologist at Tufts Universitv in Medford, Miss. The onlv care these”sur- ’ ’ ‘ / \ /

faces require is an occasional wipe to re- move dead bacteria, the researchers say.

Lewis and his colleagues altered the surface chemistry of glass slides by coat- ing them with polymer molecules of a class known to destroy bacteria in water. The scientists found that the slides coat- ed with long and rigid versions of the polymers killed between 94 and 100 per- cent of four types of bacteria sprayed on- to them. They report their findings in the

MY OF SCIENCES. When one end of each bacteria-killing

molecule binds to the glass, its other end can penetrate a bacterium’s cell mem- brane and kill the microbe, conjectures team member Alexander M. Klibanov, a chemist at the Massachusetts Institute of Technology. The most effective polymer is known as hexyl-PVP.

Bacteria are not likely to develop a re- sistance to this killing mechanism, as they do to other methods (see related story, this page), because no single gene could make the membrane invincible. Another benefit: The newly designed sur-

May 22 PROCEEDINGS OF THE NATIONAL ACADE-

A chemically modified glass slide (left) kills bacteria that thrive on an ordinary glass slide (right).

knobs, toys, and pay phones, for exam- ple, he says. Such a coating would be at- tractive to him personally, says Klibanov, speaking to SCIENCE NEWS from a pay phone. “You don’t know who touched the phone before you did,” he notes.

The coating does not kill all the bacte- ria that land on it, comments Jonathan Dordick, a chemical engineer at Rensse- laer Polytechnic Institute in Troy, N.Y. However, the figures cited by the re- searchers are “a pretty good start,” he says, and the new method is both simple and elegant. He adds, “I can’t think of any solution like this that’s been done for airborne microbes.” -J. Gorman

MAY 26,2001 SCIENCE NEWS, VOL. 159 325