The location of microorganisms also must be considered when factors affecting the efficacy of germicides are assessed. Medical instruments with multiple pieces must be disassembled and equipment such as endoscopes that have crevices, joints, and channels are more difficult to disinfect than are flat- surface equipment because penetration of the disinfectant of all parts of the equipment is more difficult.
Only surfaces that directly contact the germicide will be disinfected, so there must be no air pockets and the equipment must be completely immersed for the entire exposure period.
Manufacturers should be encouraged to produce equipment engineered for ease of cleaning and disinfection. Microorganisms vary greatly in their resistance to chemical germicides and sterilization processes Figure 1 Intrinsic resistance mechanisms in microorganisms to disinfectants vary. For example, spores are resistant to disinfectants because the spore coat and cortex act as a barrier, mycobacteria have a waxy cell wall that prevents disinfectant entry, and gram-negative bacteria possess an outer membrane that acts as a barrier to the uptake of disinfectants , Implicit in all disinfection strategies is the consideration that the most resistant microbial subpopulation controls the sterilization or disinfection time.
That is, to destroy the most resistant types of microorganisms i. Except for prions, bacterial spores possess the highest innate resistance to chemical germicides, followed by coccidia e. The germicidal resistance exhibited by the gram-positive and gram-negative bacteria is similar with some exceptions e. Rickettsiae , Chlamydiae , and mycoplasma cannot be placed in this scale of relative resistance because information about the efficacy of germicides against these agents is limited Because these microorganisms contain lipid and are similar in structure and composition to other bacteria, they can be predicted to be inactivated by the same germicides that destroy lipid viruses and vegetative bacteria.
A known exception to this supposition is Coxiella burnetti , which has demonstrated resistance to disinfectants With other variables constant, and with one exception iodophors , the more concentrated the disinfectant, the greater its efficacy and the shorter the time necessary to achieve microbial kill.
Generally not recognized, however, is that all disinfectants are not similarly affected by concentration adjustments. For example, quaternary ammonium compounds and phenol have a concentration exponent of 1 and 6, respectively; thus, halving the concentration of a quaternary ammonium compound requires doubling its disinfecting time, but halving the concentration of a phenol solution requires a fold i. Considering the length of the disinfection time, which depends on the potency of the germicide, also is important.
Several physical and chemical factors also influence disinfectant procedures: temperature, pH, relative humidity, and water hardness. For example, the activity of most disinfectants increases as the temperature increases, but some exceptions exist. Furthermore, too great an increase in temperature causes the disinfectant to degrade and weakens its germicidal activity and thus might produce a potential health hazard.
An increase in pH improves the antimicrobial activity of some disinfectants e. The pH influences the antimicrobial activity by altering the disinfectant molecule or the cell surface Water hardness i. Organic matter in the form of serum, blood, pus, or fecal or lubricant material can interfere with the antimicrobial activity of disinfectants in at least two ways.
Most commonly, interference occurs by a chemical reaction between the germicide and the organic matter resulting in a complex that is less germicidal or nongermicidal, leaving less of the active germicide available for attacking microorganisms.
It is generally agreed that the selection and dissemination of resistant bacteria in nature should be avoided in order to ensure effective treatment against infectious diseases in humans and maintain an ecological balance that favors the predominance of a susceptible bacterial flora in nature.
The indiscriminate use of antimicrobial agents may disrupt the microbial balance in favor of resistance bacteria. In particular, wastewater from hospital plants could play a role in the selection of resistance bacteria in sewage 6, We want to thank Ing.
Abrir menu Brasil. Brazilian Journal of Microbiology. Abrir menu. Moretton About the authors. Microbiological analyses Total heterotrophic count - Serial fold dilutions of samples were prepared in physiological saline, and 0. Antimicrobial susceptibility testing The iodineresistant subpopulation of effluent was selected from the bacterial population by treating wastewater samples 4 minutes with iodine 0.
Bacterial identification and test of sensitivity to the biocides Bacteria tolerant to each disinfectant were identified by different biochemical test, according to the Manual of Clinical Microbiology The susceptibility of the isolated strains to each disinfectant was analyzed: MIC values of chlorhexidine were determined on tryptic soy agar TSA plates containing a range of chlorhexidine concentrations ppm , inoculated with 0.
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Plasmid-mediated resistance to some other biocides in Gram-negative bacteria and in staphylococci has been described, but its significance remains uncertain. As to the future, there is a need to establish conclusively whether there is a clear-cut linkage between antibiotic and biocide resistance in non-sporulating bacteria and whether biocides can select for antibiotic resistance.
Additionally, the responses to biocides of new and emerging pathogens must be assessed. At the same time, continuing research is necessary to establish further the underlying mechanisms of resistance and to provide more efficient means of bacterial inactivation.
Abstract Bacterial resistance to antibiotics is a long-established, widely-studied problem.
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