The antimicrobial polymer PHMB enters cells and selectively condenses bacterial chromosomes

Abstract

To combat infection and antimicrobial resistance, it is helpful to elucidate drug mechanism(s) of action. Here we examined how the widely used antimicrobial polyhexamethylene biguanide (PHMB) kills bacteria selectively over host cells. Contrary to the accepted model of microbial membrane disruption by PHMB, we observed cell entry into a range of bacterial species, and treated bacteria displayed cell division arrest and chromosome condensation, suggesting DNA binding as an alternative antimicrobial mechanism. A DNA-level mechanism was confirmed by observations that PHMB formed nanoparticles when mixed with isolated bacterial chromosomal DNA and its effects on growth were suppressed by pairwise combination with the DNA binding ligand Hoechst 33258. PHMB also entered mammalian cells, but was trapped within endosomes and excluded from nuclei. Therefore, PHMB displays differential access to bacterial and mammalian cellular DNA and selectively binds and condenses bacterial chromosomes. Because acquired resistance to PHMB has not been reported, selective chromosome condensation provides an unanticipated paradigm for antimicrobial action that may not succumb to resistance.

Comparing two polymeric biguanides: chemical distinction, antiseptic efficacy and cytotoxicity of polyaminopropyl biguanide and polyhexamethylene biguanide

“…Recent research further supports the interaction with bacterial membranes as the mode of action for PHMB, stating that it disturbs the first layer of the membrane lipid bilayer (Chadeau et al, 2012) by electrostatic as well as hydrophobic interactions and dehydration (Souza et al, 2015). However, a new study also strengthened the hypothesis of additional mechanisms of the bactericidal effect of PHMB based on the interaction of the infiltrated substance with bacterial chromosomes (Chindera et al, 2016). In this work, PHMB was shown to enter bacterial cells and condense chromosomes as well as arrest cell division, ultimately leading to the death of treated bacteria.…”

“…Also, Chindera et al (2016) demonstrated that despite an uptake of PHMB into several mammalian cell lines, no transition into nuclei occurs owing to entrapment of PHMB in endosomes. As a consequence, PHMB displays an excellent combination of bactericidal efficacy and low cytotoxicity to mammalian cells.…”

“…Since being a strong base and positively charged cationic biocide, the antiseptic potential of PHMB relies on interaction with acidic, negatively charged phospholipids in the bacterial membrane as well as interaction with bacterial chromosomes after penetration of the membrane barrier. This results in the elimination of micro-organisms through increased fluidity, permeability and loss of integrity as well as chromosome condensation and the disruption of bacterial metabolism when transferred into the bacterial cell (Chindera et al, 2016;Hubner & Kramer, 2010). PHMB is effective against planktonic Gram-positive and Gram-negative bacteria as well as biofilms and a variety of other species such as Saccharomyces cerevisiae, Candida albicans and Acanthamoeba (reviewed by Kaehn, 2010).…”

Adverse health effects of humidifier disinfectants in Korea: lung toxicity of polyhexamethylene guanidine phosphate

“…Guanidine-based antimicrobials were thus believed to have low toxicity to humans (Ikeda et al, 1983(Ikeda et al, , 1984. However, recent accounts have reported PHMB penetrating mammalian cells and interacting with chromosomes, raising concerns about health hazards from guanidine-based antimicrobials (Allen et al, 2004(Allen et al, , 2006Chindera et al, 2016;Firdessa et al, 2015).…”

Bactericidal Activity and Physiological Effects of Combined Application of Poly-Hexamethylene Biguanide Hydrochloride and 1-bromo-3-chloro-5, 5-dimethylimidazolidine-2, 4-dione on Staphylococcus aureus

“…PHMB exhibits bacteriostatic at low concentrations (10 mg/L). It can slightly damage the cell membrane, interact with bacterial DNA, and inhibit bacterial proliferation [2,4]. No one resistant microorganism mutant has been reported after several decades of extensive use [5].…”