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.
