Can we prevent the developement of antibacterial resistance?

Antibiotic resistance - Can we trace it from animal farms to the medical clinics?

The increasing incidence of hospital acquired infections with antibiotic resistant bacteria has become a major issue in the recent past. These infections due to the resistant bacteria not only increased morbidity and mortality but also increase cost of management in the hospitals. In one study from a premier medical institute in New Delhi, it was found that methicillin resistant staphylococcus bacterial infections were present in the 7.5% - 41% of cultures from these wounds from 3 different hospitals.(1).  About one quarter of healthy people carry one or more strains staphylococci asymptomatically at any given time, and infections are commonly endogenous being caused by the patient’s colonizing strain.(2). It was observed that use of antibiotics in the farm houses results in the development of resistance bacteria and it was felt this reaches the humans. Farmers regularly treat cattle, pigs, and chickens with antibiotics to dampen low-level infections that slow the growth of these animals. But wily bacteria quickly evolve resistance. Livestock farms often brim with resistant bugs that can pass to humans and potentially spread resistance to other microbes. Most farm screens have traced resistance only in pathogenic bugs—those that cause disease. But such organisms make up just a small percentage of gut microbes in pigs, The new data, he says, suggest that the common practice of using swine waste as a fertilizer is like spreading truckloads of antibiotic resistance on farmland. Those bacteria can share their resistance with other bacteria that happen to be on crops and in downstream aquatic ecosystems—bacteria that could cause illness, Chénier says. "This is a time bomb." Employees at slaughterhouses and meat-processing facilities say that they follow guidelines to keep the pigs' gut bacteria from contaminating the rest of the meat and the facility. "Risk assessment shows that by the time food gets to the consumer, there's very little resistant bacteria left in the meat".

Ecologist Martin Chénier of McGill University in Montreal, Canada, and his colleagues examined bacteria on a university farm. This farm  in January 2007 banned all antibiotics, including two commonly used varieties: tylosin and chlortetracycline. They monitored gut bacterial populations in 10 pigs by searching for bacteria resistant to common drugs in their waste.

To the team's surprise, the entire bug community kept most of its armor against the antibiotics, even after 2 ½ years. When the researchers grew the bacteria in the lab, for example, 70% to 100% of them were still resistant to chlortetracycline when the pigs were slaughtered. "I didn't expect such high levels of resistance would remain," says Chénier, whose team will publish the results in the January issue of Microbial Ecology.

References:

1) Gadepalli R et al  Clinical and molecular characteristics of nosocomial methicillin-resistant Staphylococcus aureus skin and soft tissue isolates from three Indian hospitals J Hosp Infect. 2009 Nov;73(3):253-63. Epub 2009 Sep 25.

2)  Von Eiff C, Becker K, Machka K, Stammer H, Peters G. Nasal carriage as a source of Staphylococcus aureus bacteremia. Study Group. N Engl J Med. 2001; 344:11–26.