Biocides intrinsic

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... 

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. 

Table 13.4 Examples of intrinsic resistance mechanisms to biocides in bacteria...

Burkholderia (formeriy Pseudomonas) cepacia is intrinsically resistant to a number of biocides, notably benzalkonium chloride and chlorhexidine. Again, the outer membrane is likely to act as a permeability barrier. By contrasL Ps. stutzeri (an organism implicated in eye infections caused by some cosmetic products) is invariably intrinsically sensitive to a range of biocides, including QACs and chlorhexidine. This organism contains less wall muramic acid than other pseudomonads but it is imclear as to whether this could be a contributory factor in its enhanced biocide susceptibility. 

Intrinsic (natural, innate) resistance. In one form of intrinsic resistance, the fungal cell wall (see Chapter 2) is considered to present a barrier to exclude or, more likely, to reduce the penetration by biocide molecules. The evidence to date is sketchy but the available information tentatively links cell wall glucan, wall thickness and consequent relative porosity to the sensitivity of Saccharomyces cerevisiae to chlorhexidine. 

Biocides are by their nature intrinsically toxic, in this respect any adventitious release to the environment requires an assessment of the relative risk posed. The 5th Environmental Action Plan of the EU is committed to a substantial reduction in the use of biocides. In particular, the Biocidal Products Directive (98/08/EC) is concerned with controlling biocidal products in the market place. Compliance with this directive is required from all member states by 14th May 2000. In this context, a strategy to control the release of biocides is timely, if continued protection is to be afforded to industry and consumer alike. One approach to controlling the release of biocide is to encapsulate in an inert inorganic framework, prior to incorporation in the coating.1... 

Biocidal products are necessary for the control of organisms that are harmful to human or animal health and for the control of oiganisms that cause damage to natural or manufactured products. Although they are beneficial they can pose risks to humans, animals and the environment in a variety of ways due to their intrinsic properties and associated use patterns and therefore a comprehensive evaluation of the hazard and the risk and recommendations for safe use of such substances are required. In February... 

The Swedish Chemical Inspectorate (KEMI) has used substitution analysis to assess biocides with the goal of promoting sustainable agriculture. KEMI uses a seven-step process that evaluates not only the intrinsic... 

The intrinsic hazard or effects assessment is established from the extensive toxicological and eco-toxicological studies performed on the active substance (or the biocidal product when necessary). From this data a dose-response assessment is made and an appropriate no-effect level is derived. 

The basic idea of the CLH process is the transfer of responsibility for classification and labeling from industrial companies to authorities on a European Community level. In case of active substances in biocidal or plant protection products, all intrinsic properties including physicochemical properties, human health hazards, and environmental hazards are subject to the harmonization. By contrast, in the case of chemicals which are used in other application fields only some specific hazard classes are considered in the CLH procedure. According to Article 36 of the CLP Regulation, these are respiratory sensitization, carcinogenicity, germ cell mutagenicity, and reproductive toxicity. Consequently, these provisions have... 

Intrinsic resistance to biocides as a consequence of bacterial degradative activities is thus not a major mechanism of insusceptibility. There are, of course, examples of plasmid-mediated enzymes that confer resistance to inorganic (and sometimes organic) mercurials and these will be discussed later... 

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. 

It is also important to notice that SCFs have biocide properties against most micro-organisms (fungi, bacteria, viruses) (20-25) and, even if it cannot be considered as a real sterilizing agent, SCF processes are intrinsically sterile and never increase the bioburden. 

Chronic infections in contrast tend to be focal infections, limited in size, that wax and wane for long durations and are only partially destructive to tissues. The strategies of a single-cell, mobile, free-floating bacterium versus those of a community of bacteria encased in a self-secreted protective matrix (biofilm) are radically different and may one type of infections "chronic." Biofilm is intrinsically resistant to host immunity, antibiotics, and biocides, different treatment strategies will be required. Chronic infections such as chronic wounds, surgical-site infections, and infected implants will yield only to repetitive evaluation and multiple simultaneous therapies that require much persistence from the physician. 

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