Biocides bacterial resistance

Resistance to antimicrobial agents is of concern as it is well known that bacterial resistance to antibiotics can develop. Many bacteria already derive some nonspecific resistance to biocides through morphological features such as thek cell wall. Bacterial populations present as part of a biofilm have achieved additional resistance owkig to the more complex and thicker nature of the biofilm. A system contaminated with a biofilm population can requke several orders of magnitude more chlorine to achieve control than unassociated bacteria of the same species. A second type of resistance is attributed to chemical deactivation of the biocide. This deactivation resistance to the strong oxidising biocides probably will not occur (27). 

Bacterial resistance to biocides 5.2.2 Resistance to other biocides... 

Several factors are known to influence biocidal activity these include the period of contact, biocide concentration, pH, temperature, the presence of oigartic matter and the nature and condition of the microorgartisms being treated. Bacterial resistance to antibiotics is a well-established phenomenon and has been widely studied for luar years. By contrast, the mechanisms of insusceptibility to non-antibiotic chemical agents are less well understood. 

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. 

Table 13.2 Intrinsic and acquired bacterial resistance to biocides... 

Russell A.D. (1995) Mechanisms of bacterial resistance to biocides. Int Biodet Biodeg, 36, 247-265. Russell A.D. Chopra I. (1996) Understanding Antibacterial Action and Resistance, 2nd edn. Chichester Ellis Horwood. 

Russell AD (1998) Mechanisms of bacterial resistance to antibiotics and biocides. Prog Med Chem 35, 133-197. 

Silver, S., L.T. Phung, and G. Silver. 2006. Silver as biocides in bum and wound dressings and bacterial resistance to silver compounds. J. Ind Microbiol. Biotechnol. 33 627-634. 

Walsh, S.E. et al., Development of bacterial resistance to several biocides and effects on antibiotic susceptibility. J. Hosp. Infect. 55, 98-107, 2003. 

Bacterial resistance to both antibiotics and biocides is essentially of two types [6-8, 23-25] ... 

Much is known about the two general mechanisms, especially with regard to antibiotics. In this review, current aspects of the mechanisms of resistance of several different types of bacteria to a broad range of antibiotics and biocides will be discussed. Where relevant, the clinical significance will be addressed, and a final section will consider possible ways of overcoming bacterial resistance. 

Various mechanisms of bacterial resistance to antibiotics and biocides have been discussed. The question as to whether there is a link between resistance to chemotherapeutic drugs on the one hand and non-antibiotics on the other remains to be addressed. 

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. 

Silver-based eompounds are inereasingly being used as biocides. Silver acts by reacting with the sites at whieh microorganisms would otherwise bond and reproduce. It does not have corrosive properties and does not contribute to the build-up of bacterial resistance to antibiotics. 

In general, biocide-releasing polymers have no influence over their intrinsic antimicrobial activity. The polymers are simply acting as carriers for biocides or antibiotics. The biocidal molecules, which are incorporated in the polymer matrix and/or tethered to the polymer backbone, are released. One of the major advantages of these systems is that the release of the embedded antimicrobial active substances is controlled by the used polymeric system. Therefore, the rates of release are adjustable and polymers can release the biocides very close to the cell, which makes them efficient. However, the polymers still release biocides into the environment and will eventually become inactive. Polymeric biocides contain biocidal repeating units. Such macromolecules often show the same mode of action as their repeating units with somewhat lower activity, due to the steric hindrance caused by the polymeric backbone. Biocidal polymers distinguish themselves by the fact that they act as a whole molecule. Further, biocidal polymers have been found to show a lower tendency to build up bacterial 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. 

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... 

Intrinsic resistance may than be defined as a natural, chromosomally controlled property of a bacterial cell that enables it to circumvent the action of a biocide (see Table 13.2). A summary of intrinsic resistance mechanisms is provided in Table 13.4. 

---