An investigation into the antimicrobial mechanisms of action of two contact lens biocides using electron microscopy.

Polyquaternium-1 (PQ-1) and myristamidopropyl dimethylamine (MAPD) are biocides used commercially in a contact lens disinfecting solutions. Electron microscopy was used to provide further evidence on the mechanism(s) of action of these agents against a wide range of ocular pathogens including bacteria, fungi and protozoa. Both PQ-1 and MAPD caused multiple forms of damage to the organisms tested, evidenced by structural alterations, blebbing, leakage and cell destruction. The extent of damage and the selectivity against specific type of microorganisms was consistent with the antimicrobial activity of these agents. Although electron microscopy is a powerful tool, it has its limitations when used to examine the mode of action of biocides. Indeed, there was no evidence of gross structural alteration to Acanthamoeba castellani or Aspergillus fumigatus following treatment.

Identification and biological evaluation of grapefruit oil components as potential novel efflux pump modulators in methicillin-resistant Staphylococcus aureus bacterial strains.

Methicillin-resistant Staphylococcus aureus (MRSA) and MSSA strains were treated with: (a) grapefruit oil (GFO) components, isolated by chromatography and characterised by NMR and mass spectroscopy; (b) antimicrobial agents, or (c) a combination of both to evaluate (MIC determination) intrinsic antibacterial activity and to determine whether GFO components could modulate bacterial sensitivity to the anti-bacterial agents. Preliminary data suggested that the grapefruit component 4-[[(E)-5-(3,3-dimethyl-2-oxiranyl)-3-methyl-2-pentenyl]oxy]-7H-furo[3,2-g]chromen-7-one (2) enhances the susceptibility of test MRSA strains to agents, e.g., ethidium bromide and norfloxacin, to which these micro-organisms are normally resistant.

Aspects of the antimicrobial mechanisms of action of a polyquaternium and an amidoamine.

OBJECTIVES: Polyquad (Alcon) (polyquaternium-1, PQ-1) and Aldox (Alcon) (myristamidopropyl dimethylamine, MAPD) are two biocides that are used commercially in a contact lens disinfecting solution, namely Opti-Free Express (Alcon) multi-purpose disinfecting solution. Their potential mechanisms of action were investigated against a range of common ocular pathogens. These were Acanthamoeba castellanii (trophozoites and cysts), Aspergillus fumigatus, Candida albicans, Pseudomonas aeruginosa, Serratia marcescens and Staphylococcus aureus. METHODS: Three aspects were investigated: the lethal effects of the biocides on the organisms, the leakage of K+ from treated cells, and the lysis of spheroplasts derived from the cells. RESULTS: PQ-1 was found to have predominantly antibacterial activity, and induced K+ leakage from the bacteria and C. albicans. It also caused lysis of spheroplasts of S. marcescens, but not those of C. albicans. MAPD was active against all of the organisms, but showed higher activity against the fungi and amoeba. It induced K+ leakage from A. fumigatus and C. albicans, and like PQ-1, lysed the spheroplasts of S. marcescens but not C. albicans. CONCLUSIONS: The two biocides have different spectra of antimicrobial activity. PQ-1 has mainly antibacterial activity, whereas MAPD was active against all of the test organisms, particularly the fungi.

Performance of contact lens disinfecting solutions against Pseudomonas aeruginosa in the presence of organic load.

PURPOSE: Contact lens wearers can become noncompliant with lens disinfection procedures. The purpose of this study was to evaluate multipurpose contact lens disinfecting solutions in the presence of organic soil. METHODS: OPTI-FREE EXPRESS and three products preserved with polyhexamethylene biguanide (PHMB) were inoculated with three strains of Pseudomonas aeruginosa in organic soil. Surviving bacteria were counted at various time points, using the ISO 14729 standard method. RESULTS: Results indicated that OPTI-FREE EXPRESS was efficient in the presence of organic soil and achieved a reduction of almost 6 log. The other products were less effective under the test conditions and failed to achieve 3-log reduction of the bacteria. These products also seemed to lose activity after time, allowing surviving bacteria to multiply. Conversely OPTI-FREE EXPRESS maintained high activity for the entire 72 hours of the study. CONCLUSIONS: The results indicate that OPTI-FREE EXPRESS would remain highly efficient in the case of noncompliance with disinfection procedures.

Identification of genes involved in the susceptibility of Serratia marcescens to polyquaternium-1.

OBJECTIVES: Polyquaternium-1 (PQ-1) is a biocide used commercially in a contact lens disinfecting solution, 'Opti-Free Express (Alcon) Multi-Purpose Disinfecting Solution'. The genetic basis for resistance of Serratia marcescens to PQ-1 was investigated using a random transposon-based mutagenesis approach. METHODS: S. marcescens was subjected to random transposon mutagenesis using a mini-Tn5 Km2 transposon. Mutants with increased susceptibility to PQ-1 were selected and the disrupted genes were identified. Antibiotic susceptibility profiles were also determined for all of the mutants. RESULTS: A wide range of genes were found to be disrupted in the mutants. The most common were genes associated with the cell membranes, or involved in biosynthesis and metabolism. CONCLUSIONS: This study shows that random transposon mutagenesis is an effective tool for the elucidation of mechanisms of action and resistance to biocides. The results support our previous findings that PQ-1 is active against the cytoplasmic membrane of S. marcescens.