A study of the antibacterial activity of some polyhexamethylene biguanides towards Escherichia coli ATCC 8739.

Abstract

The antibacterial action of some polyhexamethylene biguanides upon Escherichia coli has been investigated. An amine ended dimer (AED) (n= 2), a polydisperse mixture sold by I.C.I. Limited as the active ingredient of Vantocil IB (PHMB, n= 5.5) and a high molecular weight (HMW) fraction (n≤ 10) of PHMB were used. PHMB and the high molecular weight fraction totally inhibited growth and motility of Esch. coli in liquid culture, whilst amine ended dimer never totally inhibited either function, irrespective of concentration. Growth inhibition and bacteriocidal activity increased with increasing levels of biocide‐polymerization. The three compounds, whilst being active over different concentration ranges, possessed similar concentration exponents and temperature coefficients. Cytoplasmic membrane damage and disruption of the cell envelope, indicated by loss from the cells of 260 nm absorbing materials, inorganic phosphate, and changes in permeability towards the dye 2‐p‐toluidinylnaphthylene‐6‐sulphonate, was observed at concentrations which were markedly bactericidal whilst bacteristatic concentrations caused only loss of potassium. Loss of cytoplasmic materials from treated cells in all instances followed first‐order kinetics. This indicated that irreversible damage was initiated and completed within a short time of contact between cells and biocide. Alteration of cytoplasmic membrane permeability towards various cations was assessed by measuring rates of lysis of sphaeroplasts in isotonic solutions of Na, Li and Cs acetate. For a given biocide concentration, the rates of lysis were inversely proportional to the hydrated ionic radii of the cation. This indicated that the damage to the cytoplasmic membrane was non‐specific and proportional to biocide concentration. Temperature coefficients (Q10) of approximately 2.0 for the loss of 260 nm absorbing material, inorganic phosphate and potassium from treated cell‐suspensions and bacteriocidal activity suggested that death of cells and cytoplasmic membrane damage are directly associated and are a direct result of biocide action, rather than mediated through the induction of autolytic enzymes.