ARS | Publication request: Chlorine inactivation of non-resistant and antibiotic resistant strains of Salmonella Typhimurium isolated from chicken carcasses

Submitted to: Journal of Food Protection
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: February 1, 2013
Publication Date: N/A

Interpretive Summary: Antibiotics are used on-the-farm to treat subclinical and clinical bacterial infections of poultry and in the past to promote growth and feed efficiency. Use of antibiotics in live poultry that harbor human pathogens could induce expression of defense mechanisms in the pathogen that make them more resistant to disinfectants, such as chlorine, that are applied later during poultry processing. Thus, the objective of the current study was to test the hypothesis that Salmonella Typhimurium that are resistant to antibiotics are more resistant to chlorine than Salmonella Typhimurium that are not resistant to antibiotics. Results of the present study indicated that the ability of chlorine to kill Salmonella in chilled water was the same for non-resistant and antibiotic resistant strains of Salmonella Typhimurium. Thus, it does not appear that on-farm use of antibiotics would have the unintended consequence of increasing resistance of Salmonella to chlorine applied during poultry processing.

Technical Abstract: A study was conducted to test the hypothesis that strains of Salmonella Typhimurium that are resistant to antibiotics are more resistant to chlorine than strains of S. Typhimurium that are not resistant to antibiotics. To test this hypothesis, strains (n = 16) of S. Typhimurium with four antibiotic resistance profiles were tested for their inactivation kinetics in chlorinated (30 ppm, pH 6) water at 4C. The four antibiotic resistance profiles were: 1) none; 2) tetracycline-sulfisoxazole (T-Su); 3) tetracycline-ampicillin-amoxicillin-cefoxitin-ceftiofur-sulfisoxazole (T-A-Am-C-Ce-Su); and 4) tetracycline-ampicillin-amoxicillin-cefoxitin-ceftiofur-sulfisoxazole-kanamycin (T-A-Am-C-Ce-Su-K). Inactivation of S. Typhimurium in chlorinated water displayed non-linear inactivation kinetics with a concave downward curve that fit well (R2 = 0.964) to the power law model with a shape parameter of 1.37. The time for a single log reduction (d-value) of S. Typhimurium from an initial concentration of 5.36 log/ml did not differ (P greater than 0.05) among the four antibiotic resistance groups: 1) none = 4.3; 1.2 min (mean; SD); 2) T-Su = 3.9; 0.8 min; 3) T-A-Am-C-Ce-Su = 3.8; 0.8 min; and 4) T-A-Am-C-Ce-Su-K = 4; 0.2 min with n = 4 strains per group. Thus, the hypothesis was rejected and it was concluded that expression of an antibiotic resistance phenotype does not confer cross-protection in S. Typhimurium to chlorine inactivation in chilled water.