Table 1: Parent strains are in bold and mutants are listed below their respective parents. Mutants with increased resistance to biocide compared to their parents are indicated in red.
|Strain and Genotype||Selective agent||Virkon||Superkill||AQAS||FFS|
|L357 (DT104 ‘A’)||0.4||0.025||0.1||0.2|
|F1||FFS (1X MIC)||0.2|
|F2||FFS (1X MIC)||0.2|
|L378 (CipR VLA52)||0.4||0.025||1.6||0.2|
|L108 (tolC::aph from SL1344)||0.4||0.006||<0.003||0.025|
|A26||AQAS (2X MIC)||0.12|
|L358 (MDR DT104)||0.4||0.025||1.6||0.2|
|S2||S’kill (1X MIC)||0.025|
|S22||S’kill (2X MIC)||0.025|
|S23||S’kill (2X MIC)||0.025|
|V6||V’kon (2X MIC)||0.8|
|V7||V’kon (2X MIC)||0.8|
This data clearly indicates that biocide exposure selects for strains with increased tolerance to biocides at sub-MIC concentrations and at the MIC and that there is no obvious ﬁtness cost in these strains when compared to their parents in biocide free broth.
Salmonella Typhimurium are amongst the leading causes of gastrointestinal disease and is increasingly found to exhibit multiple antibiotic resistance (MAR). Efflux is one mechanism that can confer MAR. Efflux pumps are membrane proteins that actively export a wide range of toxic substrates thereby mediating resistance to these agents as a result. The wide spectrum of substrates recognized by efflux systems has prompted concern that exposure of a bacterium to one substrate could select for overexpression of an efflux system and consequent resistance to all other substrates.
In this study, growth rates of biocide-resistant salmonella mutants were determined using absorbance at 600 nm and compared to parent strains. This data clearly indicates that biocide exposure selects for strains with increased tolerance to biocides and that there is no obvious fitness cost in these strains when compared to their parents in biocide free broth.