Comparison of antibiotic resistance patterns in Listeria monocytogenes and Salmonella enterica strains pre-exposed and exposed to poultry decontaminants

Recent opinions expressed by European Union Scientific Committees suggest there is a potential for poultry decontaminants to increase resistance to antibiotics. At this moment there is no scientific information available to estimate this risk accurately. Four strains (Listeria monocytogenes serovar 1/2a, Listeria monocytogenes serovar 4b, Salmonella enterica serotype Typhimurium and Salmonella enterica serotype Enteritidis) were repeatedly exposed to increasing sub-inhibitory concentrations of decontaminants (trisodium phosphate, acidified sodium chlorite, citric acid, chlorine dioxide or peroxyacetic acid) and tested against 15 antibiotics by means of a standard disc-diffusion technique (NCCLS). The antibiotic resistance patterns of strains were compared before and after exposure to decontaminants. Intra-specific differences in antibiotic resistance patterns were found among strains. Increases in resistance to various antibiotics were observed in L. monocytogenes and S. enterica strains after exposure to chemicals (especially ASC). These results raise concerns over the application of certain poultry decontaminants, since they could contribute to the development of microbial resistance mechanisms. However, these are preliminary results derived from laboratory-based experiments. Additional studies under practical field conditions would be needed to substantiate these findings.