Abstract
Few studies have been conducted on the susceptibility of bacteria to biocides. A total of 182 methicillin-resistant and -susceptible Staphylococcus aureus isolates collected from healthy or diseased humans and animals in Germany were included in the present study. Sixty-three isolates of animal origin and 119 human isolates were tested for their MICs to eight biocides or heavy metals by the broth microdilution method. The MIC50 and MIC90 values of human and animal isolates were equal or differed by not more than 1 dilution step, and statistical analysis revealed that differences between MICs of human and animal isolates were not significant. However, when taking into account the multilocus sequence type (MLST), a strong tendency (P = 0.054) to higher MICs of silver nitrate was detected for clonal complex 398 (CC398) isolates from humans compared to those from animals. Furthermore, a comparison of MIC values from isolates belonging to different clonal lineages revealed that important human lineages such as CC22 and CC5 exhibited significantly (P < 0.05) higher MICs for the biocides chlorhexidine, benzethonium chloride, and acriflavine than the main animal lineage sequence type 398 (ST398). Isolates with elevated MIC values were tested for the presence of biocide and heavy metal tolerance-mediating genes by PCR assays, and the following genes were detected: mepA (n [no. of isolates containing the gene] = 44), lmrS (n = 36), norA (n = 35), sepA (n = 22), mco (n = 5), czrC (n = 3), smr (n = 2), copA (n = 1), qacA and/or -B (n = 1), qacG (n = 2), and qacJ (n = 1). However, only for some compounds was a correlation between the presence of a biocide tolerance gene and the level of MIC values detected.IMPORTANCE Biocides play an essential role in controlling the growth of microorganisms and the dissemination of nosocomial pathogens. In this study, we determined the susceptibility of methicillin-resistant and -susceptible S. aureus isolates from humans and animals to various biocides and heavy metal ions and analyzed differences in susceptibilities between important clonal lineages. In addition, the presence of biocide or heavy metal tolerance-mediating genes was investigated. We demonstrated that important human lineages such as CC22 and CC5 had significantly higher MIC values for chlorhexidine, benzethonium chloride, and acriflavine than the main farm animal lineage, ST398. In addition, it was shown that for some combinations of biocides and tolerance genes, significantly higher MICs were detected for carriers. These findings provide new insights into S. aureus biocide and heavy metal tolerance.