Three research articles in this week's issue of the journal have investigated the occurrence of antibiotic-resistance bacteria in retail meats.
In the first study, researchers from Maryland, USA, identified and characterized strains of Salmonella isolated from ground meats purchased in the Washington DC area.
The bacterium was isolated from 20% of samples of ground chicken, beef, turkey, and pork purchased at three supermarkets. A total of 13 serotypes were identified.
It was found that 84% of isolates were resistant to at least one antibiotic, and 53% to at least three antibiotics. It was additionally found that 16% of isolates were resistant to ceftriaxone, the drug of choice for treating salmonellosis in children.
Author David G. White, of the Food and Drug Administration, Laurel, said on behalf of his group, "Resistant strains of Salmonella are common in retail ground meats."
"These findings provide support for the adoption of guidelines for the prudent use of antibiotics in food animals, and for a reduction in the number of pathogens present on farms and in slaughterhouses," he concluded.
In the second study, a team from the USA determined the frequency of quinupristin-dalfopristin-resistant Enterococcus faecium in samples of chickens purchased at supermarkets in four states.
The combination of quinupristin and dalfopristin was approved in the United States in late 1999 for the treatment of vancomycin-resistant E. faecium infections.
A related streptogramin, virginiamycin, has been used at subtherapeutic concentrations to promote the growth of farm animals.
Resistant bacteria were isolated from 237 of 407 (58%) chickens sampled.
| Antibiotic-resistant bacteria are common in retail meat.
| New England Journal of Medicine |
In addition, low-level resistance in E. faecium was identified in 3 out of 334 (1%) stool samples from outpatients.
Dr L. Clifford McDonald, of the National Center for Infectious Diseases, Atlanta, Georgia, concluded, "Quinupristin-dalfopristin-resistant E. faecium contaminates a large proportion of chickens sold in US supermarkets.
"However, the low prevalence and low level of resistance of these strains in human stool specimens suggest that the use of virginiamycin in animals has not yet had a substantial influence.
"Foodborne dissemination of resistance may increase, however, as the clinical use of quinupristin-dalfopristin increases."
Antibiotic-resistant enterococci are often present in retail meats, but it is unclear whether the ingestion of these contaminants leads to sustained intestinal carriage.
In the final study, a Danish team investigated this problem.
Resistant strains of Enterococcus faecium, obtained form chicken and pork, were ingested by 12 healthy volunteers.
Various concentrations of these same strains were isolated from the stools of all subjects, for up to 2 weeks.
The investigators found that the organisms survived gastric passage and multiplied, and were then transiently present in stool.