Antimicrobial resistance of bacterial flora associated with bovine products in South Africa

The administration of subtherapeutic doses of antibiotics to livestock intr oduces selective pressures that may lead to the emergence and dissemination of resistant bacteria. This study determined the antibiotic-resistance spe ctra of the microbial flora found on freshly slaughtered and retail beef an d in unpasteurized and pasteurized packaged milk. Staphylococci, Enterobact eriaceae, and isolates from total aerobic plate counts were tested for resi stance to vancomycin, streptomycin, methicillin, tetracycline, and gentamic in using the disc diffusion susceptibility test and resistance to penicilli n was determined by using oxacillin. A larger proportion of resistance to m ost antibiotics, except for vancomycin, was displayed by isolates from abat toir samples. The incidence of multiple antibiotic resistance (MAR) pathoge nic bacteria is also higher in the abattoir. Resistance genes lost because of lack of selective pressure or resistant flora being replaced by more sen sitive flora during processing is the reason for the lower incidence of MAR pathogenic bacteria among retail samples. These resistant bacteria can be transferred to humans through the consumption of rare or raw beef and unpas teurized milk, thus rendering the resultant food-related infections difficu lt to treat. The present findings clearly demonstrate that antibiotic-resis tant bacteria in beef and milk pose a serious problem in South Africa.