Antimicrobial drug resistance of Salmonella and Escherichia coli isolates from cattle feces, hides, and carcasses

To determine patterns of cross-contamination and antibiotic susceptibility of microorganisms commonly associated with cattle, 60 cattle shipped to a commercial abattoir (20 in each of three separate trial periods) were followed through processing. Samples for bacterial isolation were collected from the feces and hides immediately before shipping, from the hides at the abattoir after exsanguination, and from the carcasses before evisceration and in the cooler. Samples were cultured for Salmonella and non-type-specific Escherichia coli. Salmonella was identified in 33.9% (n = 20) of the fecal samples and on 37.3% (n = 22) of the hides before shipment. At the abattoir, the proportion of hides from which Salmonella was isolated increased (P < 0.001) to 84.2% (48 hides). Nonspecific E. coli and Salmonella were recovered from 40.4 and 8.3% of preevisceration carcass samples, respectively. No Salmonella or nonspecific E. coli were recovered from hotbox carcass samples. Isolates were tested for antimicrobial drug susceptibility. For nonspecific E. coli, 80.3% (n = 270) of the isolates were resistant to at least one antimicrobial drug. For Salmonella, 97% (n = 101) of the isolates were resistant to at least one antimicrobial drug; however, only 4.0% were resistant to two or more. The most common resistance was to sulfamethoxazole. These results indicate that the presence of microorganisms resistant to antimicrobial drugs is common in cattle and beef. Further studies are needed to identify the sources and causes of this drug resistance.