Role of Porins in the Susceptibility of Mycobacterium smegmatis and Mycobacterium chelonae to Aldehyde-Based Disinfectants and Drugs

Abstract

Nosocomial outbreaks attributable to glutaraldehyde-resistant, rapidly growing mycobacteria are increasing. Here, evidence is provided that defects in porin expression dramatically increase the resistance of Mycobacterium smegmatis and Mycobacterium chelonae to glutaraldehyde and another aldehyde disinfectant, ortho-phthalaldehyde. Since defects in porin activity also dramatically increased the resistance of M. chelonae to drugs, there is thus some concern that the widespread use of glutaraldehyde and ortho-phthalaldehyde in clinical settings may select for drug-resistant bacteria.Rapidly growing mycobacteria (RGM) are ubiquitous in hospitals' water sources and cause outbreaks in health care settings throughout the world (7,22,23,31). Among the effective options for the disinfection of semicritical, temperature-sensitive medical devices, glutaraldehyde (GTA) remains the most widely used chemical disinfectant in hospitals worldwide due to its effective mycobactericidal activity and relatively low cost (Fig. 1). Recent reports suggest, however, that RGM are being isolated with increasing frequency from washer disinfectors and GTA-processed endoscopes, with recent Mycobacterium chelonae and Mycobacterium massiliense outbreaks being associated with the development of resistance to GTA (4,8,10,17,30).GTA is thought to be predominantly a surface-reactive biocide which forms bridges or cross-links with amino groups of proteins exposed at the surface of bacterial cells (17). Although the mechanisms of resistance of mycobacteria to the disinfectant are not known, it is thus reasonable to assume that changes in the cell surface resulting in decreased binding and/or penetration of GTA may be mechanisms through which RGM develop resistance. Because of the significant role played by the mycobacterial outer membrane in drug susceptibility (3, 12) and host-pathogen interactions (5), there is thus some concern that the widespread use of GTA in clinical settings selects for resistant populations of bacteria, with possible consequences on antibiotic resistance and pathogenicity.Amino group-containing compounds susceptible to binding GTA at the surface of RGM include surface-exposed proteinsamong which are porins-and glycopeptidolipids. In addition, cell wall (lipo)polysaccharides have been proposed to affect the susceptibility of M. chelonae to GTA (15). To assess the impact of these cell envelope compounds on the resistance of Mycobacterium smegmatis to GTA, mc 2 155 isogenic mutants deficient in different aspects of their biosynthesis (Table 1) were compared to their respective wild-type (WT) parent for GTA resistance, using the suspension test described by Griffiths et al. (10). Mutants deficient in other factors known to significantly affect the susceptibility of M. smegmatis to biocides, such as phosphatidylinositol mannosides, the Lsr2 protein, and mycothiols, were also included in this study. The mutants fell into roughly three categories: (i) those whose susceptibility to GTA was not significantly altered (mc 2 155⌬MSMEG4...

Resistance of Acanthamoeba Cysts to Disinfection Treatments Used in Health Care Settings

“…Resistance of Acanthamoeba trophozoites to glutaraldehyde raises important questions about the potential association of glutaraldehyde-resistant Acanthamoeba with nontuberculous mycobacteria (NTM) that can also resist glutaraldehyde and grow within amoebae (18,23,58). It has been demonstrated that the resistance of NTM to glutaraldehyde is at least partially due to mutations in cell wall porins and that these mutations also increase the resistance of NTM to antibiotics commonly used to treat these infections (53). Furthermore, mutations in the same genes also increase the intra-amoebal survival capacity of NTM (49).…”

Diagnosis and Management of Atypical Mycobacterial Infection after Laparoscopic Surgery

“…A recent study has shown that atypical mycobacteria such as M. chelonae and M. smegmatis are showing increased resistance to these chemicals due to defects in porin expression in the bacterial cell walls [14]. Porins are cell wall proteins found in Mycobacteria and have been known to create channels that allow the passage of small hydrophilic molecules, such as antibiotic drugs, through the highly hydrophobic mycobacterial cell wall [15].…”

Mycobacterium massiliense BRA100 strain recovered from postsurgical infections: resistance to high concentrations of glutaraldehyde and alternative solutions for high level disinfection

“…Although 2% GTA resistance is considered a rare event in mycobacteria, RGM strains with low susceptibility to GTA have already been described, most of them related to M. chelonae species [17][18][19] . Nomura et al 18 submitted 4 randomly selected M. chelonae isolates recovered from bronchoscope washing machines to GTA suspension tests.…”

“…The results indicated viable and reproducible mycobacterial cells even after 60-min exposure to this biocide. Svetlíkova et al 19 have proposed that defects of mycobacterial porins may be possibly represent the main mechanisms involved in resistance to aldehyde-based disinfectants.…”