|Farrington,, Leigh - TEXAS A&M UNIVERSITY|
|Inskip, Peter - TEXAS A&M UNIVERSITY|
Submitted to: Journal of Food Protection
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: May 7, 2001
Publication Date: October 1, 2001
Interpretive Summary: There is increasing concern about the emergence of antibiotic resistant bacteria and their threat to human health. It has been questioned whether the use of antibiotics in animal production has promoted antibiotic resistance. We studied the antibiotic resistance patterns of Salmonella bacteria isolated from swine in a commercial operation. Many of the Salmonella were resistant to multiple antibiotics, although routine antibiotic usage on these farms had been discontinued for the previous five years.
Technical Abstract: Antimicrobial resistance levels were examined for 365 Salmonella isolates recovered from the lymph nodes (n=224) and cecal contents (n=141) of market-age swine at slaughter. Antimicrobial resistance testing for 13 common antibiotics was performed by disk diffusion. Although none of the antibiotics tested were used subtherapeutically within the last five years on the farms sampled, resistance to chlortetracycline, penicillin G, streptomycin and sulfisoxazole was common. Penicillin G resistance was significantly more frequent (P=0.03) and sulfisoxazole resistance was significantly less frequent (P<0.01) in lymph node versus cecal isolates. Multidrug resistance was observed among 94.7% of the lymph node isolates and 93.5% of the cecal isolates. The most frequent multidrug resistance pattern included three antibiotics - penicillin G, streptomycin and chlortetracycline. Isolates in somatic serogroup B, and more specifically, S. agona and S. schwarzengrund isolates, were often resistant to a greater number of antibiotics than were isolates in the other serogroups. Streptomycin, sulfisoxazole, ampicillin (lymph node isolates) and nitrofurantoin (cecal isolates) resistance levels differed significantly between somatic serogroups. The prevalence of penicillin G-, streptomycin- and sulfisoxazole-resistant isolates differed significantly between serovars for both lymph node and cecal isolates. Results of this study suggest that a correlation existed between the somatic serogroup or serovar of a Salmonella isolate and its antimicrobial resistance status which is specific to the antibiotic of interest and the source of the isolate (lymph node versus cecal contents).