Polihexanide

Polihexanide (PHMB) is mostly bactericidal at 0.016–0.02% (1 h) and yeasticidal at 0.1% (5 min). Fungicidal and mycobactericidal activity is species dependent. Its antimicrobial activity is explained by membrane damage. Cellular defence mechanisms include biodegradation of PHMB in A. westerdijkiae, Sphingomonas spp. and Azospirillum spp., tolerance genes in S. cerevisiae and E. coli and point mutation in P. lilacinum. PHMB reduces biofilm mass in developing and existing biofilms in several species. The effect of PHMB on biofilm fixation is unknown. High MIC values indicating tolerance to PHMB have been reported for isolates of P. lilacinum (50,000 mg/l). Low-level exposure results in no MIC change in 32 species, a weak MIC change in 18 species and a strong MIC change in 6 species, which are only stable in E. faecalis and S. aureus, resulting in MIC values as high as 31.3 mg/l (E. faecalis) and 23.5 mg/l (S. aureus). Cross-tolerance to other biocidal agents has not been reported. Cross-resistance to gentamicin has been reported in E. coli. PHMB-resistant isolates have been described in an outbreak of keratitis (Fusarium spp.) and with contaminated disinfectants (P. lilacinum). The overall probability of resistance to PHMB of practical relevance is low in the absence of biofilm.