between biocides and bacteria that would lead to the expression of global resistance mechanisms, putting in perspective the during-use concentration of a product and its effect.
Primarily a low concentration attained during product preparation and use (including phase separation for emulsion where the antimicrobial is retained in the oil phase)
The use of contaminated diluent during product preparation
Improper storage of biocidal products
The use of contaminated dispensers holding biocidal products
The use of contaminated disinfectant cloth to disinfect a sterile product
Bacterial exposure to increasing concentration of a biocide in defined conditions of time, growth media, and temperature. Such protocols, often referred to as stepwise training of bacteria to biocide exposure, do not necessarily reflect conditions of exposure found in practice.94,95,96,97,98,99,100,101,102,103,104,105
The use of environmental isolates from health care, biocide manufacturing sites, slaughterhouses, etc, where biocidal products are commonly used. Bacterial isolates often show a reduced biocide susceptibility profile or resistance to specific biocides.78,80,84,96,106,107,108,109,110,111,112,113,114,115,116
Studies investigating biocidal product contamination that lead to an infectious outbreaks or pseudooutbreaks (see Table 4.1)
TABLE 4.1 Outbreaks and pseudo-outbreaks due to contaminated biocidal producta
concentration, has been well reported (see Table 4.1). The artificial development of bacterial resistance, however, can be difficult to achieve using realistic in vitro protocols, reflecting, for example, high biocide concentrations or short contact time.6,98 Nevertheless, it is now clear that bacteria can use an accumulation of mechanisms, ensuring their survival in biocides and certain biocidal products.
FIGURE 4.1 Levels of biocide interactions with a bacterial cell. Abbreviation: PMF, proton motive force.
Factors inherent to the biocide including concentration, formulation, mechanism(s) of action
Factors inherent to the bacteria including the type (ie, mycobacteria, gram-negative or gram-positive bacteria, bacterial endospores), metabolism (including presence of a biofilm), specific resistance mechanism (eg, overexpression of efflux pumps)
Factors inherent to product usage (ie, the during-use parameters), decreased concentration (ie, following dilution of stock solution or abundant rinsing with water, residual concentration), type and amount of organic load (soiling), effective exposure time, material/surface that is disinfected
account for bacterial survival in products (see Table 4.1). The concentration of a biocide in a product is key for its efficacy or for allowing bacterial survival.122 Where the biocide concentration is close to the MBC, the product may allow bacterial survival and be prone to bacterial contamination.123 During the use of a product, it is often difficult to predict what will be the target microorganisms to kill. In health care settings, outbreaks of Clostridium difficile will dictate the use of sporicides, which are considered the most effective disinfectant products.124,125 However, despite claims from manufacturers, not all biocide chemistries are sporicidal and only oxidizing agents and alkylating agents have been shown to have efficacy against bacterial endospores.124,125,126 Different microorganisms are recognized to have different susceptibility to biocides.8 The main reason for being less susceptible to biocides is their intrinsic or natural properties, which are mainly structural including different cell envelope (eg, different membrane lipid composition, different outer membrane proteins [OMP]) or additional components (eg, efflux, glycocalyx). Bacterial endospores have all together a unique structure and are considered to be highly resistant to biocides (see following discussion). As such, they are often used as biological indicators for testing high-level disinfection of medical devices. Hence, a sporicidal product should be effective in killing vegetative microorganisms.8 Apart from their intrinsic properties, a bacterium can acquire resistance to a biocide through gene transfer and mutations.127 Whether the change in biocide susceptibility profile is transient or permanent, the mechanisms involved are often similar and initially result from the selective pressure exerted by the biocide or biocidal product in the first place.15,128
the efflux pump gene expression is dependent on the concentration of the biocide.171,182,183
TABLE 4.2 Examples of studies reporting carriage of efflux pump genes in environmental, food, and hospital isolates