What are the factors that influence the effectiveness of cleaning, disinfection, and sterilization?

Number and location of microorganisms

With all other conditions remaining constant, the higher the number of microbes, the more time is required for a disinfectant solution to destroy them all. Spaulding illustrated this relationship when he used identical test conditions and demonstrated that it takes 30 minutes to destroy 10 spores of B. atrophaeus (formerly Bacillus subtilis), but 3 hours to destroy 100,000 spores of Bacillus atrophaeus. This reinforces the need for scrupulous cleaning of medical instruments before disinfection and sterilization. Reducing the number of microorganisms that must be inactivated through meticulous cleaning increases the margin of safety when the germicide is used according to labeling and shortens the exposure time required to destroy the entire microbial load. Researchers have also demonstrated that aggregated or clumped cells are more difficult to inactivate than monodispersed cells.

The location of microorganisms must also be considered when evaluating factors affecting the efficacy of germicides. Medical instruments with multiple parts must be disassembled, and equipment such as endoscopes that have crevices, joints, and channels are harder to disinfect than equipment with flat surfaces, because penetration of the disinfectant into all parts of the equipment is more difficult. Only surfaces that come into direct contact with 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 designed to facilitate cleaning and disinfection. KLINTENSIV DEZICON® – High-level concentrated disinfectant

Innate resistance of microorganisms

Microorganisms vary greatly in their resistance to chemical germicides and sterilization processes. The mechanisms of intrinsic resistance of 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 the penetration of disinfectants, and gram-negative bacteria possess an outer membrane that acts as a barrier to the absorption of disinfectants.

Implicitly, in all disinfection strategies, it is considered that the most resistant microbial subpopulation controls the sterilization or disinfection time. In other words, to destroy the most resistant types of microorganisms (e.g., bacterial spores), the user must use the exposure times and concentration of germicide necessary to achieve complete destruction. Except for prions, bacterial spores possess the highest innate resistance to chemical germicides, followed by coccidia (e.g., Cryptosporidium), mycobacteria (e.g., M. tuberculosis), non-enveloped or small viruses (e.g., poliovirus and coxsackievirus), fungi (e.g., Aspergillus and Candida), vegetative bacteria (e.g., Staphylococcus and Pseudomonas), and lipid or medium-sized viruses (e.g., herpes and HIV).

The germicidal resistance manifested by gram-positive and gram-negative bacteria is similar, with some exceptions (e.g., P. aeruginosa, which shows greater resistance to some disinfectants). P. aeruginosa is also significantly more resistant to a variety of disinfectants in its “natural” state than cells subcultured on laboratory media.

Rickettsiae, Chlamydiae, and mycoplasma cannot be placed on this scale of relative resistance, because information on the efficacy of germicides against these agents is limited. Since these microorganisms contain lipids and are similar in structure and composition to other bacteria, it can be predicted that they will be inactivated by the same germicides that destroy lipid viruses and vegetative bacteria. A known exception to this assumption is Coxiella burnetii, which has demonstrated resistance to disinfectants.

Concentration and efficacy of disinfectants

Under conditions where other variables are constant and with one exception (iodophors), the more concentrated the disinfectant, the greater its efficacy and the shorter the time required to achieve microbial destruction. However, it is generally not recognized that not all disinfectants are affected in the same way 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 the disinfection time, but halving the concentration of a phenol solution requires a 64-fold increase (i.e., 26) in disinfection time.

It is also important to consider the duration of the disinfection time, which depends on the potency of the germicide. This was illustrated by Spaulding, who demonstrated, using the mucin loop test, that 70% isopropyl alcohol destroyed M. tuberculosis in 5 minutes, while a simultaneous test with 3% phenolic required 2-3 hours to achieve the same level of microbial destruction. OXOKLIN High-level disinfectant

Physical and chemical factors

Several physical and chemical factors also influence disinfection procedures: temperature, pH, relative humidity, and water hardness. For example, the activity of most disinfectants increases with increasing temperature, but there are some exceptions. Moreover, an excessive increase in temperature causes the degradation of the disinfectant and weakens its germicidal activity, thus potentially creating a health hazard.

An increase in pH improves the antimicrobial activity of some disinfectants (e.g., glutaraldehyde, quaternary ammonium compounds), but decreases the antimicrobial activity of others (e.g., phenols, hypochlorites, and iodine). pH influences antimicrobial activity by modifying the disinfectant molecule or the cell surface.

Water hardness (i.e., a high concentration of divalent cations) reduces the rate of destruction of certain disinfectants because the divalent cations (e.g., magnesium, calcium) in hard water interact with the disinfectant to form insoluble precipitates.

Organic and inorganic matter

Organic matter in the form of serum, blood, pus, or fecal or lubricant matter can interfere with the antimicrobial activity of disinfectants in at least two ways. Most commonly, interference occurs through a chemical reaction between the germicide and the organic matter, resulting in a less germicidal or non-germicidal complex, leaving less active germicide available to attack the microorganisms. Chlorine and iodine disinfectants, in particular, are prone to such an interaction. Alternatively, organic material can protect microorganisms from attack by acting as a physical barrier.

The effects of inorganic contaminants on the sterilization process were studied in the 1950s and 1960s. These and other studies show that the protection of microorganisms by inorganic contaminants in all sterilization processes results from occlusion in salt crystals. This further underscores the importance of meticulous cleaning of medical devices before any sterilization or disinfection procedure, as both organic and inorganic soils are easily removed by washing. Concentrated enzymatic disinfectant detergent

Duration of exposure

Items must be exposed to the germicide for an appropriate minimum contact time . Several researchers have demonstrated the efficacy of low-level disinfectants against vegetative bacteria (e.g., Listeria, E. coli, Salmonella, VRE, MRSA), yeasts (e.g., Candida), mycobacteria (e.g., M. tuberculosis), and viruses (e.g., poliovirus) at exposure times of 30-60 seconds. By law, all applicable instructions on the label of products registered by competent authorities must be followed. If the user selects exposure conditions that differ from those on the registered product label, the user assumes responsibility for any injury resulting from off-label use and may be subject to regulatory enforcement action.

All lumens and channels of endoscopic instruments must come into contact with the disinfectant. Air pockets interfere with the disinfection process, and objects floating on the disinfectant will not be disinfected. The disinfectant must be reliably introduced into the internal channels of the device. The exact disinfection times for medical items are somewhat elusive due to the effect of the aforementioned factors on disinfection efficiency. Certain contact times have proven reliable, but in general, longer contact times are more effective than shorter ones.

Biofilms

Microorganisms can be protected from disinfectants by the production of thick masses of cells and extracellular materials, or biofilms. Biofilms are microbial communities that are tightly attached to surfaces and cannot be easily removed. Once these masses are formed, the microbes within them can be resistant to disinfectants through several mechanisms, including the physical characteristics of older biofilms, genotypic variation of the bacteria, microbial production of neutralizing enzymes, and physiological gradients within the biofilm (e.g., pH). Bacteria in biofilms are up to 1,000 times more resistant to antimicrobials than the same bacteria in suspension. Although new decontamination methods for removing biofilms are being investigated, chlorine and monochloramines can effectively inactivate bacteria in biofilm. KLINPOOL® – Chlorine-based disinfectant

Researchers have hypothesized that glycocalyx-like cell masses on the interior walls of polyvinyl chloride pipes would protect embedded organisms from some disinfectants and serve as a reservoir for continuous contamination. Biofilms have been discovered in whirlpool tubs, water lines of dental units, and numerous medical devices (e.g., contact lenses, pacemakers, hemodialysis systems, urinary catheters, central venous catheters, endoscopes). Their presence can have serious implications for immunocompromised patients and for patients who have permanent medical devices. Some enzymes and detergents can degrade biofilms or reduce the number of viable bacteria within a biofilm.