Chloroxylenol- and triclosan-tolerant bacteria from industrial sources—susceptibility to antibiotics and other biocides

This study aimed to determine the degree of susceptibility of several industrial bacterial isolates tolerant to para-chloro-meta-xylenol, triclosan, three other commonly used biocides, and to a range of clinically significant antibiotics. Minimum inhibitory concentrations (MICs) of benzalkonium chloride, chlorhexidine and phenol were determined and compared with those of standard strains. When elevated MICs were exhibited, suspension efficacy tests were carried out to assess the lethal efficacy of these biocides. Antibiotic sensitivity profiles were initially determined by disk diffusion testing, and antibiotic MICs by a gradient plate method. Biocide MICs were largely similar between industrial and standard strains, although isolates of Acinetobacter johnsonii showed elevated benzalkonium chloride MICs, which were not reflected in terms of lethal effects. Antibiotic sensitivities did not vary greatly between strains. An industrial triclosan-tolerant strain of Citrobacter freundii showed a slightly higher resistance to some antibiotics, but in most cases this was recorded as “sensitive” according to the guidelines used. Chloramphenicol resistance was shown in the triclosan-tolerant strain of A. johnsonii, but also in the sensitive revertant strain, suggesting that this property is intrinsic to the strain and unrelated to triclosan tolerance. This study did not produce evidence suggesting that tolerance to triclosan or para-chloro-meta-xylenol in industrial bacterial isolates promotes the emergence of tolerance to other biocides or increases resistance to antibiotics.