Table 4.
Mechanisms conferring biocide resistance in bacteria
| Mechanism | Effect | Example of structures (and microorganisms) |
|---|---|---|
| Decrease in biocide concentration | ||
| Impermeability barrier | Decrease the amount of a biocide that penetrates in the cell | Spore coats (bacterial spores), LPS (Gram-negative bacteria), mycoylarabinogalactan layer (mycobacteria) |
| Multidrug efflux pumps | Decrease the amount of a biocide within the cell | QacA-D, QacG and QacH, Nor A (Staphylococcus aureus), MexAB-OprM, MexCD-OprJ, MexEF-OprN, MexJK, QacE, QacΔ1 (Pseudomonas aeruginosa), QacE, SilABC (Klebsiella pneumoniae), AcrAB-TolC, AcrEF-TolC, EmrE (Escherichia coli) |
| Degradation | Inactivate a biocide outside or within a cell | Hydrolase and reductase (E. coli; S. aureus), aldehyde dehydrogenase (E. coli, P. aeruginosa), catalases, superoxide dismutase and alkyl hydroxyperoxidasesa (E. coli) |
| Alteration of target(s) and metabolism | ||
| Modification of target | Render the effect of a biocide ineffectiveb | Enoyl-acyl carrier reductase (S. aureus; E. coli; Mycobacterium smegmatis). |
| Multiplication of targets | Decreases the effective concentration of a biocide | Interaction with bacterial glycocalyx (in biofilm) |
| Alteration of metabolism | Decrease the detrimental effect of a biocide | Phenotypic alteration and “persisters” (bacterial biofilm) |
a
Reduction of free radicals within the cell (eg, following exposure to an oxidising agent);
b
Has only been observed with the bisphenol triclosan.