Variation in Salmonella Resistance to Poultry Chemical Decontaminants, Based on Serotype, Phage Type, and Antibiotic Resistance Patterns

Abstract

Chemical decontaminants are currently under review for final approval by the European Union authorities with the aim of reducing the number and/or prevalence of pathogenic microorganisms on poultry. The purpose of the research being reported here was to determine the association, if any, of decontaminant resistance with the serotype, phage type, and antibiotic resistance of Salmonella strains. Sixty poultry isolates of Salmonella enterica (serotypes Enteritidis: phage types 1, 4, 4b, 6a, 14b, and 35; Typhimurium; Newport; Infantis; Poona; Virchow; Agona; Derby; and Paratyphi B) showing resistance to none (sensitive), one (resistant), two, three, four, five, six, seven, or nine (multiresistant) antibiotics were screened for resistance to 1,000 ppm acidified sodium chlorite, 1.2% trisodium phosphate, or 25% citric acid. D-values (seconds required for 1-log reduction in the number of bacteria) in peptone water, using a linear regression, of Salmonella in the presence of acidified sodium chlorite varied widely with serotype (the highest resistance levels were shown by serotypes Typhimurium, Newport, and Derby) and antibiotic resistance pattern (average values of 8.37±1.69 s for multiresistant strains as compared with 5.96±0.54 s for sensitive, P < 0.05). A positive relationship (0.775, P < 0.001) was found between acidified sodium chlorite D-values and the number of antibiotics to which strains were resistant. Both serotype and antibiotic resistance had only a slight influence over Salmonella resistance to trisodium phosphate, with average D-values from 12.44±0.91 s (sensitive strains) to 13.28±0.77 s (multiresistant) (P < 0.05). Neither serotype nor antibiotic profile was associated with Salmonella resistance to citric acid (average D-value of 12.20±0.81 s). Minimal differences in resistance to decontaminants were found among Salmonella Enteritidis phage types. Results in the present study highlight the importance of selecting an adequate strain (serotype and antibiotic resistance pattern) when acidified sodium chlorite and trisodium phosphate are tested against Salmonella to ensure that concentrations capable of inactivating all strains are used.