Chlorine Inactivation of Nonresistant and Antibiotic-Resistant Strains of Salmonella Typhimurium Isolated from Chicken Carcasses†

Abstract

A study was conducted to test the hypothesis that strains of Salmonella Typhimurium that are resistant to antibiotics are more resistant to chlorine in chilled water than strains of Salmonella Typhimurium that are not resistant to antibiotics. To test this hypothesis, strains (n = 16) of Salmonella Typhimurium with four antibiotic resistance profiles were tested for their inactivation kinetics in chlorinated (30 ppm, pH 6) water at 4°C. The four antibiotic resistance profiles were (i) none; (ii) tetracycline-sulfisoxazole (T-Su); (iii) tetracycline-ampicillin-amoxicillin-cefoxitin-ceftiofur-sulfisoxazole (T-A-Am-C-Ce-Su); and (iv) tetracycline-ampicillin-amoxicillin-cefoxitin-ceftiofur-sulfisoxazole-kanamycin (T-A-Am-C-Ce-Su-K). Inactivation of Salmonella Typhimurium in chlorinated water displayed nonlinear 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 Salmonella Typhimurium from an initial concentration of 5.36 log/ml did not differ (P > 0.05) among the four antibiotic resistance groups and ranged from 3.8 to 4.3 min for 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 Salmonella Typhimurium to chlorine inactivation in chilled water.