Reversal of the surface effects of chlorhexidine diacetate on cells of Providencia stuartii

Chlorhexidine diacetate (CHA) increased the hydrophobicity of the cell surface of cells of three strains of Providencia stuartii. Removal of at least some of the CHA from the cells by washing them with an appropriate antidote partially reversed the hydrophobicity-increasing action of the biguanide. The effects of other treatments on cell surface hydrophobicity were examined with these strains and, for comparison, with two strains each of Escherichia coli and Pseudomonas aeruginosa: ethyl-enediamine tetraacetic acid affected all strains, although not to the same extent, whereas thermal injury (55°C) produced marked changes only with the two E. coli strains.     

Effect of chlorhexidine diacetate and benzalkonium chloride on the viability of wild type and envelope mutants of Escherichia coli and Pseudomonas aeruginosa

The effects of chlorhexidine diacetate and benzalkonium chloride on the viability of a wild type strain and its envelope mutants of both Escherichia coli and Pseudomonas aeruginosa are described. The nature of the findings in relation to outer membrane penetrability is considered, as is the effect of solid and liquid media on the action of the inhibitors.     

Sensitivities of wild-type and envelope-defective strains of Escherichia coli and Pseudomonas aeruginosa to antibacterial agents

The sensitivities of Escherichia coli DCO (wild type) and DC2 (envelope mutant) and Pseudomonas aeruginosa 799 (wild-type) and 799/61 (envelope mutant) to preservatives and antibiotics have been determined. The outer membrane appears to play an important role in limiting the penetration of some, but not all, antibacterial agents.     

Quenching of the antibacterial activity of chlorhexidine and benzalkonium by Letheen broth and Letheen agar in relation to wild-type and envelope mutant strains of gram-negative bacteria

Letheen broth and Letheen agar have been investigated for their ability to act as neutralising and recovery media for wild-type and envelope mutants exposed to chlorhexidine diacetate and benzalkonium chloride. At high dilutions, untreated cells of the envelope mutant of Pseudomonas aeruginosa 799/61 were unable to produce colonies on Letheen agar. As a result of various procedures, it was concluded that dilution in Letheen broth and plating in Isosensitest agar was a suitable method for quenching cationic bactericides without harming the test strains, and that the increasing use of Gram-negative bacteria with outer membrane defects means that considerable care may be necessary in selecting media for evaluating bactericidal activity.