Possible mechanisms for the relative efficacies of ortho-phthalaldehyde and glutaraldehyde against glutaraldehyde-resistant Mycobacterium chelonae

Aims: This investigation compared glutaraldehyde (GTA)-sensitive and -resis tant strains of Mycobacterium chelonae and examined the effects of pretreat ment of GTA-sensitive and -resistant strains of Myco. chelonae with chemica l agents that interfere with cell wall synthesis. Methods and Results: When exposed to 2% (v/v) GTA at 25 degreesC, GTA-resis tant strains of Myco. chelonae dried on to glass carriers were not inactiva ted to any significant extent. By contrast, GTA-sensitive strains of Myco. chelonae and a strain of Myco. terrae suffered a > 6 log reduction in viabi lity in 5 min. However, ortho-phthalaldehyde (OPA; 0.5% w/v) achieved a cor responding inactivation against two GTA-resistant strains within 5-10 and 1 0-20 min, respectively. Electron microscopy, using a non-aldehyde fixation process and also negative staining, failed to detect any extensive changes in GTA-sensitive and -resistant cultures exposed to GTA or OPA. Thin-layer chromatography was unsuccessful in detecting differences between GTA-resist ant and -sensitive strains of Myco. chelonae. However, pretreatment of GTA- resistant cells with mycobacterial cell wall synthesis inhibitors increased their subsequent susceptibility further to OPA but not to GTA. Conclusions: Ortho-phthalaldehyde is an effective new biocidal agent that, at its in-use concentration, is rapidly bactericidal to non-sporulating bac teria, including GT-sensitive and -resistant mycobacteria. Significance and Impact of the Study: Pretreatment of GTA-resistant cells w ith mycobacterial cell wall synthesis inhibitors increased their subsequent susceptibility to OPA but not to GTA.