Antibiotic-biocide linked resistance

Various mechanisms of bacterial resistance to antibiotics and biocides have been discussed. The question as to whether there is a link between resistance to chemotherapeutic drugs on the one hand and non-antibiotics on the other remains to be addressed. 

An association between antibiotic resistance and chlorhexidine and QAC resistance in Providencia stuartii and Proteus has been observed, but no evidence of a plasmid link obtained [25, 73, 287,288]. Chlorhexidine hypersensitivity has been noted in ciprofloxacin-resistant variants of Ps. aeruginosa [289] and vancomycin- and gentamicin-resistant strains of E. faecium retained sensitivity to the /usbiguanide [289, 290] and to other biocides [270-272], Anderson et al. [272] studied the inactivation kinetics of VRE and vancomycin-sensitive enterococci (VSE) exposed to environmental disinfectants at concentrations well below (extended dilutions) the recommended use-dilutions and found no differences in susceptibility of VRE and VSE. This type of approach is much more relevant than the widespread usage of MICs to measure responses to biocides. 

Clearly, efflux is a major mechanism of multidrug resistance and several authors [41, 42, 71] are now reconsidering reduced drug accumulation in terms of efflux rather than as cellular impermability. It is, however, pertinent to query whether efflux of biocides is of relevance in relation to the concentrations employed in practice and whether biocides are responsible for selecting antibiotic-resistant strains as has been suggested. Clearly, much future experimentation is needed to establish a direct link between antibiotic and biocide resistances. 

Within these two broad types of resistance, several biochemical mechanisms are known, including reduced uptake, enzymatic inactivation, target site modification and enhanced efflux. The last mentioned is assuming greater importance as additional studies are undertaken. A direct link between antibiotic and biocide resistance remains to be established. 

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