Comparative analysis of the susceptibility to triclosan and three other biocides of avian Salmonella enterica isolates collected 1979 through 1994 and 2004 through 2010.

Few studies have been conducted on changes in the susceptibility of bacteria due to long-term use of biocides. A total of 375 avian Salmonella isolates collected in Germany from healthy or diseased animals during two time periods, 1979 through 1994 and 2004 through 2010, were included in the present study. The isolates were tested for their MICs of triclosan, acriflavine, benzalkonium chloride, and chlorhexidine by broth macrodilution. MIC50, MIC90, and the distribution of MICs were compared. The MIC ranges were 0.0625 to 0.5 µg/ml for triclosan, 16 to 256 µg/ml for acriflavine, 8 to 128 µg/ml for benzalkonium chloride, and 0.5 to 32 µg/ml for chlorhexidine. MIC50s and MIC90s were equal or differed by not more than one dilution step. For isolates from healthy poultry collected during the two time periods, statistical analysis revealed a significant increase only in MICs for chlorhexidine. Salmonellae from diseased birds were more susceptible to triclosan and benzalkonium chloride but less susceptible to acriflavine and chlorhexidine. Overall, only 25 strains had the highest detected MIC of 0.5 µg/ml triclosan, but an association with multidrug resistance could not be confirmed.