Microbiological quality of ground beef from conventionally-reared cattle and "raised without antibiotics" label claims.

The contamination of the food supply with pathogens and antimicrobial-resistant bacteria has emerged as an important health concern. We compared the microbiological quality of 77 samples of ground beef from conventionally raised cattle with 73 samples of ground beef from cattle raised without antimicrobial agents. Contamination with coliforms (1.7 log CFU/g) and Escherichia coli (0.51 log CFU/g) and Shiga toxin 2-producing E. coli (6% prevalence) was similar in both sample groups. Neither Salmonella. E. coli O157, nor vancomycin-resistant enterococci were isolated from any sample. Prevalence of E. coli resistant to ampicillin (39%), amoxicillin/clavulanic acid (23%), ceftriaxone (5%), tetracycline (19%), streptomycin (19%), kanamycin (11%), sulfamethoxazole/trimethoprim (2%), and gentamicin (1%) was similar in both groups. E. coli resistant to ciprofloxacin was not identified. Resistance to ceftiofur and chloramphenicol was more prevalent in beef from conventionally raised cattle at 18 and 30%, respectively, compared to 5 and 12% prevalence in beef from cattle raised without antimicrobial agents. These results do not correlate with the frequency of subtherapeutic use of these two antibiotics in beef production. Other factors in addition to, or in lieu of, the subtherapeutic use of specific antimicrobial agents in the preharvest stages of beef production may contribute significantly to the occurrence of antimicrobial-resistant bacteria in ground beef.