Plasmids and bacterial resistance to biocides.

Plasmid-encoded bacterial resistance to antibiotics and to anions and cation (including important mercurial and silver compounds) has been widely studied. Plasmid-mediated resistance to organic cationic agents which are important biocides has been described for chlorhexidine and quaternary ammonium compounds (and also for the less important acridine, diamidines and ethidium bromide) in antibiotic-resistant Staphylococcus aureus and Staph. epidermidis strains. Plasmids may also encode reduced biocide susceptibility of Gram-negative bacteria, but intrinsic resistance is likely to be of greater significance. Antibiotic resistance and biocide resistance may be linked but this is not always found clinically.