Mycobacteria biocide resistance

Mycobacteria are more resistant than other non-sporulating bacteria to a wide range of biocides. Examples of such organisms axe Mycobacterium tuberculosis, theM avium-intracellulare (MAI) group andM. chelonae (M. chelonei). Of the bacteria, however, the most resistant of all to biocides are bacterial spores, e.g. Bacillus subtilis, B. cereus. 

Bacterial resistance to biocides (Table 13.2) is usually considered as being of two types (a) intrinsic (innate, natural), a natural property of an organism, or (b) acquired, either by chromosomal mutation or by the acquisition of plasmids or transposons. Intrinsic resistance to biocides is usually demonstrated by Gram-negative bacteria, mycobacteria and bacterial spores whereas acquired resistance can result by mutation or, more frequently, by the acquisition of genetic elements, e.g. plasmid- (or transposon-) mediated resistance to mercury compounds. Intrinsic resistance may also be exemplified by physiological (phenotypic) adaptation, a classical example of which is biofilm production. 

Other hand, mycobacteria and espeeially bacterial spores are much more resistant. A major reason for this variation in response is associated with the chemical composition and stmcture of the outer cell layers such that there is restricted uptake of a biocide, hi... 

Impermeability (Mycobacteria) Chlorhexidine QACs Organomercurials Glutaraldehyde Waxy cell wall prevents adequate biocide entry Reason for high resistance of some strains of M.chelonael... 

Many years ago, it was proposed [105] that resistance of mycobacteria to QACs was related to the lipid content of the cell wall thus, M. phlei (with low total lipid) was more sensitive than M. tuberculosis, which possessed a higher total cell lipid content. It was also pointed out [105] that the resistance of various species of mycobacteria was related to the content of waxy material in the wall. As noted above, the mycobacterial cell wall is highly hydrophobic with a mycoylarabinogalactanpeptidoglycan skeleton. Hydrophilic type biocides are generally unable to penetrate the cell wall in sufficiently high concentration to produce a lethal effect. However, low concentrations... 

Bacterial resistance to antibiotics and biocides is essentially of two types, intrinsic and acquired. Whilst the latter is of greater significance clinically with antibiotics, specific examples of intrinsic resistance to both antibiotics, e.g. mycobacteria, and biocides (e.g. mycobacteria, Gram-negative bacteria, spores) are also of importance. 

As already pointed out, staphylococci and streptococci are generally more sensitive to biocides than Gram-negative bacteria examples are provided in Table 18.4. On the other hand, mycobacteria and especially bacterial spores are much more resistant. A major reason for this variation in response is associated with the chemical composition and structure of the outer cell layers such that there is restricted uptake of a biocide. In consequence of this cellular impermeability, a reduced concentration of the antimicrobial compound is available at the target site(s) so that the cell may escape severe injury. Another, less frequently observed, mechanism is the presence of constitutive, biocidedegrading enzymes. 

Mycobacteria are generally considered to be of intermediate resistance to biocides, including aldehydes, between bacterial spores and other vegetative cells [90], Formalin, aqueous formaldehyde solution and glutaraldehyde are mycobactericidal, although some mycobacterial strains show increased resistance [90, 101, 236]. 

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