Unit 3. section 1(2).pptx

Unit 3: Control of Microorganisms Section 1: Control of microbial growth ( chapter 13) 13.1 Controlling Microbial Growth Microbial control • External measures to keep pathogens away from body • Fomites- Inanimate object that serves to transmit disease Microbial Control Resistance: Highest - b...

Unit 3: Control of Microorganisms Section 1: Control of microbial growth ( chapter 13) 13.1 Controlling Microbial Growth Microbial control • External measures to keep pathogens away from body • Fomites- Inanimate object that serves to transmit disease Microbial Control Resistance: Highest - bacterial endospores Moderate - protozoan cysts - zygospores - naked viruses: hepatitis B; poliovirus - bacteria: Mycobacterium tuberculosis, Staphylococcus aureus and Pseudomonas Least - other bacteria - fungal spores and hyphae - enveloped viruses - yeast - protozoan trophozoites Microbial Control Methods of microbial control for use on fomites • Sterilization-complete destruction/removal of all living microbes, spores, and viruses on an object or in area. • Aseptic technique- steps to prevent contamination of sterile surfaces • Sanitization-remove microbes or reduce their populations to safe levels as determined by public health standards. • Disinfection- process of killing or inhibiting the growth of pathogens • Does not lead to sterilization • Ideal disinfectants should be fast acting, stable, easy to prepare, inexpensive, and easy to use. • ex: bleach Methods of microbial control for use on living tissue • Antisepsis- Application of chemicals for removal of potential pathogens from living tissue • antiseptics must be selectively effective against microorganisms and able to penetrate tissue deeply without causing tissue damage. (ex: hydrogen peroxide) • Degerming- protocol that significantly reduces microbial numbers by using mild chemicals (e.g., soap) and gentle scrubbing of a small area of skin or tissue to avoid the transmission of pathogenic microbes. ( ex: handwashing) Figure 13.4 Measuring Microbial control -cide = to kill • • • • Bactericide: destroys bacteria Fungicide: destroys fungi Viricide: destroys viruses Sporocide: destroys spores • Inactivates major enzymes of an organism and interferes with its metabolism so that it dies. Measuring Microbial control -static = stay still Bacteriostatic: inhibits/prevents the growth bacteria Fungistatic: inhibits/ prevents the growth fungi • Disrupts minor chemical reactions and slows the metabolism, which results in a longer time between cell divisions. Controlling Microorganisms. Cleaning products © Jones and Bartlett Publishers. Photographed by Kimberly Potvin Sterile Surgical Instruments. Courtesy of Journalist 2nd Class Shane Tuc/U.S Navy Measuring Microbial control • Microbial death- Permanent loss of reproductive capability; even under optimum growth conditions • Microbial death curve- graphical representation of the progress of a particular microbial control protocol • decimal reduction time (DRT) or Dvalue -amount of time it takes for a specific protocol to produce a one order of magnitude decrease in the number of organisms— death of 90% of the population Figure 13.5 • Microbial death is logarithmic and easily observed using a semilog plot instead of an arithmetic one. The decimal reduction time (D-value) is the time it takes to kill 90% of the population (a 1log decrease in the total population) when exposed to a specific microbial control protocol, as indicated by the purple bracket. Measuring Microbial control • A definite proportion of the organisms die in a given time interval • The fewer organisms present, the shorter the time needed to achieve sterility • Microorganisms differ in their susceptibility to antimicrobial agents • The most susceptible phase for most organisms is the logarithmic growth phase Measuring Microbial control Factors that affect effectiveness of microbial control protocol: • length of exposure • microbial load • nature of the microbe • action of the agent • temperature • pH • presence of solvents, interfering organic matter and inhibitors: Large amounts of saliva, blood and feces can inhibit the action of disinfectants and even heat Microbial death curve 13.2 Using Physical Methods to Control Microorganisms 1)Heat • Fast, reliable, inexpensive • Heat is applied above the maximal range for microbial growth, destroying cellular enzymes, which become irreversibly denatured • Important application in food industry • Thermal death time –minimal time necessary for killing population at a given temperature • Thermal death point- minimal temperature at which organism dies in a given time Dry heat • kills bacteria by oxidizing cellular components • Slower than moist heat Applications of dry heat • Incineration- uses direct flame, burns to ashes • Examples • Flaming a loop- Placing loop containing bacteria directly in flame • Flaming mouth of tube gets rid of dust, and organisms that come into contact with mouth of tube • Bactericenerator • Incineration of carcasses of animals infected with deadly disease: anthrax Figure 13.6 (a) Sterilizing a loop, often referred to as “flaming a loop,” is a common component of aseptic technique in the microbiology laboratory and is used to incinerate any microorganisms on the loop. (b) Alternatively, a bactericinerator may be used to reduce aerosolization of microbes and remove the presence of an open flame in the laboratory. These are examples of dry-heat sterilization by the direct application of high heat capable of incineration. (credit a: modification of work by Anh-Hue Tu; credit b: modification of work by Brian Forster) Applications of dry heat • Hot-air oven sterilization• Uses radiating dry heat for sterilization • Does not penetrate materials easily • Long periods of exposure to high temperatures necessary • Temperatures include 160oC for 2 hours( ensures destruction spores) • 180oC for 1 hour Applications of dry heat • Hot-air oven sterilization• Preferred over moist heat when sterilizing: • glassware to avoid any residual moisture that can contaminate the surface • Metallic medical instruments since dry heat is non-corrosive for metals • Powders, oils, and petroleum jelly since moist heat cannot penetrate grease. Moist heat • Kills bacteria by coagulating/denaturing proteins • Protein denaturation requires less energy than oxidation. Thus, less heat is required. • Faster than dry heat since water molecules conduct heat better than air. • Can be used at a lower temperature and shorter exposure time than dry heat. Applications of moist heat • Boiling• Most microorganisms, as well as eukaryotic spores, can be killed within 10 minutes with viruses requiring 30 minutes and bacterial spores requiring 2 hours • Not reliable as sterilization procedure Temperature and the Physical Control of Microorganisms. Applications of moist heat • Autoclaving-moist heat as pressurized steam • Heating for 15- 20 minutes at 121oC with 15 pounds of pressure per inch2. The pressure allows the temperature to rise above 100oC to 121oC. • prions are highly resistant (134oC for 18 min) • Used to control microorganisms in both hospitals and labs • Used for blankets, bedding, utensils, instruments • Important in making media Figure 13.7 (a) An autoclave is commonly used for sterilization in the laboratory and in clinical settings. By displacing the air in the chamber with increasing amounts of steam, pressure increases, and temperatures exceeding 100 °C can be achieved, allowing for complete sterilization. (b) A researcher programs an autoclave to sterilize a sample. (credit a: modification of work by Courtney Harrington; credit b: modification of work by Lackemeyer MG, Kok-Mercado Fd, Wada J, Bollinger L, Kindrachuk J, Wahl-Jensen V, Kuhn JH, Jahrling PB) Monitoring the Effectiveness of the Autoclave Figure 13.8 • The white strips on autoclave tape (left tube) turn dark during a successful autoclave run (right tube). (credit: modification of work by Brian Forster) Monitoring the Effectiveness of Autoclave Sterilization. Vials containing spores of Geobacillus stearothermophilus are suspended in a growth medium containing a pH indicator. Following autoclaving, the vial is incubated at 35°C. If the autoclave run was effective, all spores will be killed and the solution will remain purple. If the spores were not killed (an ineffective sterilization process), they will germinate and grow. The acid the cells produce will turn the pH indicator yellow. »» What do you know about Applications of moist heat • Prevacuum autoclave• draws air out of sterilizing chamber at the beginning of the cycle • A vacuum pump operates at the end of cycle to remove the steam and dry the load • Minimal exposure time for sterilization and reduced time to complete the cycle. • 132oC to 134oC at pressure of 28-30lb/in2 for as little as 4 minutes. Applications of moist heat • Fractional sterilization/Tyndallization-moist heat without pressurized steam • free flowing steam at 100oC for 30 minutes on each of three consecutive days • Kills all vegetative cells on first day but not spores • Then viable cells resulting from the germination of spores are killed on the following days • Relies on having the proper conditions for germination of spores • Used for materials that cannot be sterilized by other methods Applications of moist heat • Pasteurization-heating food to a specific temperature and then cooling immediately. • Invented by Pasteur to destroy microbes that caused wine to sour • Does not achieve sterility: use of lower temperatures to destroy only pathogenic organisms. • Does not affect bacterial spores. • In fruit juices, targets enteric bacteria like Salmonella and E. coli. • In the case of milk, destroys yeast, Mycobacterium tuberculosis, Coxiella burnetii (hay fever). Applications of moist heat • Holding(batch) pasteurization method • Heating at 63oC for 30 minutes • High-Temperature Short-Time(HTST)/ Flash pasteurization • 71.6oC for 15 seconds • Most commonly used method • Ultra pasteurization method (UHT) • 140oC for 3 seconds • Kills all bacteria • Used for organic milk since product has to travel longer Figure 13.9 • Two different methods of pasteurization, HTST and UHT, are commonly used to kill pathogens associated with milk spoilage. (credit left: modification of work by Mark Hillary; credit right: modification of work by Kerry Ceszyk) 2) Cold: Refrigeration and Freezing • Low temperatures slow spoilage by lowering metabolic rate of microorganisms • Refrigerator: ~4oC • Freezer: ~-18oC • Ultra low freezer: ~-70oC • Liquid Nitrogen ~-196oC • Limitations: psychrotrophs Figure 13.10 • Cultures and other medical specimens can be stored for long periods at ultra-low temperatures. (a) An ultra-low freezer maintains temperatures at or below −70 °C. (b) Even lower temperatures can be achieved through freezing and storage in liquid nitrogen. (credit a: modification of work by “Expert Infantry”/Flickr; credit b: modification of work by USDA) 3) Desiccation (Dehydration) • Used in preparation of various meats, fish, cereals, and other foods • Salting induces water to diffuse out of microorganisms via osmosis • Lyophilization- item is rapidly frozen (“snap-frozen”) and placed under vacuum so that water is lost by sublimation. • Limitations: fungi can tolerate low water Figure 13.12 (a) The addition of a solute creates a hypertonic environment, drawing water out of cells. (b) Some foods can be dried directly, like raisins and jerky. Other foods are dried with the addition of salt, as in the case of salted fish, or sugar, as in the case of jam. (credit a: modification of work by “Bruce Blaus”/Wikimedia Commons; credit raisins: modification of work by Christian Schnettelker; credit jerky: modification of work by Larry Jacobsen; credit salted fish: modification of work by “The Photographer”/Wikimedia Commons; credit jam: modification of work by Kim Becker) 4) Radiation gamma rays A. Ionizing radiation: X, • X and gamma rays both undergo ionizing radiation • consists of photons and/or moving particles (alpha, beta)that have sufficient energy to knock electrons out of the shells from either an atom or molecule, thus forming an ion. • Ions generated quickly combine with H2O, affecting metabolism and physiology • Used to • sterilize • • • • • heat-sensitive pharmaceuticals like vitamins, hormones, antibiotics plastic items like Petri plates, intravenous tubing latex items like gloves Sutures Tissues for transplantation • Preserve and extend the shelf life of food: irradiation of gamma rays produced during the natural decay of cobalt-60 or cesium-137. Pasteurizing dose used. • Limitations: Does not kill bacterial endospores, inactivate viruses, or neutralize toxins Figure 13.14 (a) Foods are exposed to gamma radiation by passage on a conveyor belt through a radiation chamber. (b) Gamma-irradiated foods must be clearly labeled and display the irradiation symbol, known as the “radura.” (credit a, b: modification of work by U.S. Department of Agriculture) 4)Radiation UV rays B. Nonionizing radiation: • Non- ionizing radiation • Has a wavelength between 100 and 400nm, with 265nm(germicidal) being most destructive to cells • When DNA absorbs UV light of sufficient intensity and for enough time, thymine dimers are induced. • This disrupts DNA replication, as well as protein synthesis and the cell dies • Limits airborne, surface contamination Figure 10: The Ionizing and Electromagnetic Spectrum of Energies. Figure 13.13 (a) UV radiation causes the formation of thymine dimers in DNA, leading to lethal mutations in the exposed microbes. (b) Germicidal lamps that emit UV light are commonly used in the laboratory to sterilize equipment. 4) Radiation Microwaves B. Nonionizing radiation: • are basically extremely high frequency radio waves, and are made by various types of transmitters. • In a microwave oven, the food is cooked inside out. • Microwaves vibrate mainly water molecules, causing friction and thus heat to defrost and cook foods. • Fats and sugars also absorb microwaves. • They are not absorbed by plastics, glass, ceramics. • 2 minutes of microwaving on full power is enough to kill or inactivate 99% of all bacterial cells and endospores on a sponge. A sponge can be microwaved to kill microbial contaminants. Courtesy of Jeffrey Pommerville 4) radiation • Deinococcus radiodurans: Able to survive 1000X the amount of radiation that would kill a human 5)filtration • Mechanical method that can be used to remove microorganisms from a solution or gas. • Important in separation of viruses from bacteria (manufacture of vaccines) • Can be used to sterilize substances that are destroyed by heat (drugs, serum, vitamins, sucrose) • To collect microorganisms from air and water samples (water quality testing) 5) filtration • Types of filters • High-efficiency particulate air(HEPA) filter • Consists of a mat of randomly arranged fibers that trap particles, microorganisms, and spores. • Can trap over 99% of all particles, including microorganisms and spores with a diameter larger than 0.3um • Incorporated into biological safety cabinets, surgical units, burn units, specialized treatment facilities Figure 13.15 (a) HEPA filters like this one remove microbes, endospores, and viruses as air flows through them. (b) A schematic of a HEPA filter. (credit a: modification of work by CSIRO; credit b: modification of work by “LadyofHats”/Mariana Ruiz Villareal) 5) filtration • Types of filters • Membrane filter- pad of cellulose acetate or polycarbonate mounted in a flask along with a vacuum pump • As fluid passes through the filter, organisms are trapped in the pores of the filter pad • Filter pad placed on a media plate plate incubated overnight colony count Figure 13.16 • Membrane filters come in a variety of sizes, depending on the volume of solution being filtered. (a) Larger volumes are filtered in units like these. The solution is drawn through the filter by connecting the unit to a vacuum. (b) Smaller volumes are often filtered using syringe filters, which are units that fit on the end of a syringe. In this case, the solution is pushed through by depressing the syringe’s plunger. (credit a, b: modification of work by Brian Forster) Figure 13.17 Figure 13.18 A Concept Map Summarizing the Physical Methods of Microbial Control. 13.3 Using Chemicals to Control Microorganisms Principles of chemical control • Physical control of microorganisms generally serves the process of killing all microorganisms(sterilization) • Chemical control primarily targets pathogenic microorganisms • Disinfection- process of killing or inhibiting the growth of pathogens • Disinfectant-A chemical used to kill or inhibit pathogenic microorganisms on a lifeless object such as a table top.( phenolic compounds, hypochlorites, quaternary salts) • Antiseptic-a chemical used to reduce or kill pathogenic microorganisms on a living object, such as the surface of the human body. • (alcohols, iodine solution, silver nitrate) • Note: A chemical agent can be used as both as disinfectant and antiseptic but the concentration would vary. Sample Uses of Antiseptics and Disinfectants. Types of disinfectants and antiseptics • Phenolic compounds • Phenol (carbolic acid) Remember Joseph Lister? Figure 13.9a • Standard for comparison against other disinfectants/antiseptics • Active against Gram positive • Inactivate enzymes, denature proteins, especially in cell membrane • Limitations: not effective as antiseptic: expensive, pungent odor, caustic to skin Types of disinfectants and antiseptics • Phenol derivatives• Greater germicidal activity and lower toxicity than phenol • Hexylresorcinol: mouthwash, topical creams, throat lozenges • Reduces surface tension Types of disinfectants and antiseptics • Phenol derivatives• Bisphenols- combination of two phenol compounds • Prominent in modern disinfection and antisepsis Hexachlorophen e Figure 13.9c Orthophenylphenol-used in Lysol and Amphyl, control Figure 13.9b bacterial and fungal growth on oHexachlorophene ( bisphenol) - Phenylphenol harvested citrus fruits toothpastes, deodorants, bath soaps is the activedisrupts ingredient Triclosancellinmembranes pHisoHex. by blocking synthesis of lipids Antibacterial soaps, lotions, kitchen Triclosa sponges, cutting boards n Chlorhexidine-surgical scrub, hand wash, superficial skin wound cleanser Types of disinfectants and antiseptics • Heavy metals- donate electrons and large atomic weight • Combine with proteins and inactivate them: form disulfide bridges between proteins, disrupting metabolism , and thereby killing the organism • Skin antiseptics, swimming pools, water supply • Limitations: not sporicidal Figure 13.21 • Heavy metals denature proteins, impairing cell function and, thus, giving them strong antimicrobial properties. (a) Copper in fixtures like this door handle kills microbes that otherwise might accumulate on frequently touched surfaces. (b) Eating utensils contain small amounts of silver to inhibit microbial growth. (c) Copper commonly lines incubators to minimize contamination of cell cultures stored inside. (d) Antiseptic mouthwashes commonly contain zinc chloride. (e) This patient is suffering from argyria, an irreversible condition caused by bioaccumulation of silver in the body. (credit b: modification of work by “Shoshanah”/Flickr; credit e: modification of work by Herbert L. Fred and Hendrik A. van Dijk) Types of disinfectants and antiseptics • Mercury- very toxic and activity reduced in presence organic matter • Less toxic when combined other compounds • Merbromin , thimerosal- combined with carrier compounds and less toxic to skin • Thimerosal used previously as preservative in vaccine • Silver – as AgNO3, useful as antiseptic and disinfectant • Copper- active against chlorophyllobtaining organisms, especially algae • Used in swimming pools, fish tanks, and municipal water supplies as copper sulfate Types of disinfectants and antiseptics • Halogens- iodine and chlorine commonly used as disinfectants • Oxidize cell components: inactivate enzymes by causing the release of atomic oxygen • Combine with ions in water • Active against Gram positive and negative bacteria, algae, protozoa, viruses, and biofilms • Killing within 30 minutes of application • Used in: municipal pools, hospitals, factories, purification of water • Limitations: Cannot destroy spores Types of disinfectants and antiseptics • Available as • inorganic compounds • gas form(ClO2) • bleach paper, sterilize medical equipment • solid form (NaClO(bleach) , Ca(ClO)2) • Clump cellular proteins • Organic compounds • Chloramines- disinfection drinking water • Iodophors- iodine linked to solubilizing agent • Reduces surface tension and reacts with enzymes in ETC and proteins in cell wall • Release iodine over a long time without staining tissues or fabrics • Povidone- iodine(Betadine)- wounds, antisepsis before incision Figure 13.22a Some Practical Applications of Disinfection with Chlorine Compounds. Types of disinfectants and antiseptics • Alcohols• EtOH • Active against vegetative cells • Denatures proteins, dissolves lipids • Strong dehydrating agent • Hand sanitizers, used to treat skin before venipuncture • Limitations: skin infections • Isopropyl alcohol • Rubbing alcohol Figure 13.24 Types of disinfectants and antiseptics • Surfactants • Soaps-chemical compounds of fatty acids combined • with potassium or sodium hydroxide. • Ph 8 • Not considered disinfectants or antiseptics • Work primarily as degerming agents, and surfactants• emulsify and solubilize particles attached to surfaces by reducing the surface tension Figure Types of disinfectants and antiseptics • Surfactants • Detergents • Strong surfactants • Attracted to phosphate groups of cellular membrane Types of disinfectants and antiseptics • Most useful are quaternary ammonium salts-cationic derivatives of Ammonium chloride • These react with cell membranes and can destroy some bacterial species and enveloped viruses • Bacteriostatic, especially Gram-positive, little odor • Benzalkonium chloride, cetylpyridinium chloride • Sanitizing agents for food prep surfaces, industrial equipment, food utensils, skin antiseptics, mouthwashes, contact lens cleaners • Limitations: reduced activity when mixed with soaps, certain Gram negative bacteria can grow in them Figure 13.26 (a) Two common quats are benzalkonium chloride and cetylpyridinium chloride. Note the hydrophobic nonpolar carbon chain at one end and the nitrogen-containing cationic component at the other end. (b) Quats are able to infiltrate the phospholipid plasma membranes of bacterial cells and disrupt their integrity, leading to death of the cell. Types of sterilizing agents • Alkylating agents • Cross link nucleic acids and proteins by reacting with amino and hydroxyl groups. • Replace hydrogen atoms with alkyl groups Types of sterilizing agents • Alkylating agents • Aldehydes • Formaldehyde: embalming fluid, inactivation of viruses in certain vaccines, and toxins(toxoids) • Glutaraldehyde: destroys bacterial cells within 10 to 30 minutes and spores in 10 hours • Sterilization delicate objects like optical equipment • Limitations: gives off irritating fumes, instruments must be thoroughly rinsed Types of sterilizing agents • Alkylating agents • Gases • Ethylene oxide • Microbicidal and sporicidal • cold sterilization, making it useful for the sterilization of heat-sensitive items • Used to sterilize paper, plastics, leather, wood, metal, and rubber, interplanetary space capsules • Good for items within plastic bags (highly penetrating) • In medicine: catheters, artificial heart valves, heart-lung machine components, optical equipment • Limitations: carcinogenic, skin irritant, and highly explosive Figure 13.29 (a) Alkylating agents replace hydrogen atoms with alkyl groups. Here, guanine is alkylated, resulting in its hydrogen bonding with thymine, instead of cytosine. (b) The chemical structures of several alkylating agents. Types of disinfectants and antiseptics • Peroxygens • Peroxides- compounds containing oxygen single bonds • Hydrogen peroxide- used as a rinse in wounds, scrapes, and abrasions • Broken down by catalase in tissue • Results in superoxide radical which is toxic to bacteria • Loosens dirt, debris, and dead tissue • Benzoyl peroxide- active ingredient in teeth whitening and to treat acne 13.4 Testing the Effectiveness of Antiseptics and Disinfectants Categories of effectiveness of chemical disinfectants • High-level germicides • have the ability to kill vegetative cells, fungi, viruses, and endospores, leading to sterilization, with extended use. • Intermediate-level germicides • are less effective against endospores and certain viruses • low-level germicides • kill only vegetative cells and certain enveloped viruses, and are ineffective against endospores. What makes a chemical agent a good disinfectant or antiseptic? • Able to kill or slow the growth of microorganisms • Nontoxic to animals or humans, especially if it is an antiseptic • Readily available • Inexpensive • Soluble in water • Effective in diluted form • Not separate on standing • Substantial shelf life • Non-corrosive • Able to perform its job in a relatively short time Factors to consider when selecting a disinfectant or antiseptic • Temperature- keep in mind that reaction that occurs at body temp may not occur at room temp • pH- some chemicals only effective at particular pH • Stability- May prefer slower reaction when long –term disinfection is desired • Type of microorganism targeted- Gram positive more susceptible Pseudomonas can grow in disinfectants and antiseptics M. tuberculosis resistant to many disinfectants • Type of surface to be treated- wound or bench Evaluating effectiveness of disinfectants and antiseptics • 1) Phenol coefficient(PC)- number indicating disinfecting ability of an antiseptic or disinfectant in comparison to phenol under identical conditions. • Agent is mixed with standardized bacterial species • Test which dilutions kill the organisms after a 10 minute exposure • Limitations: Does not take into account temperature variations, toxicity, or presence in organic matter Figure T02: Phenol Coefficients of Some Common Antiseptics and Disinfectants. Evaluating effectiveness of disinfectants and antiseptics • 2) Disk Diffusion Method • involves applying different chemicals to separate, sterile filter paper disks. • The disks are then placed on an agar plate that has been inoculated with the targeted bacterium and the chemicals diffuse out of the disks into the agar where the bacteria have been inoculated. Figure 13.31 • A disk-diffusion assay is used to determine the effectiveness of chemical agents against a particular microbe. (a) A plate is inoculated with various antimicrobial discs. The zone of inhibition around each disc indicates how effective that antimicrobial is against the particular species being tested. (b) On these plates, four antimicrobial agents are tested for efficacy in killing Pseudomonas aeruginosa (left) and Staphylococcus aureus (right). These antimicrobials are much more effective at killing S. aureus, as indicated by the size of the zones of inhibition. (credit b: modification of work by American Society for Microbiology) Evaluating effectiveness of disinfectants and antiseptics • 3) Use-dilution test• Technique for determining the effectiveness of a chemical disinfectant on a surface • standardized cultures are dried on small stainless steel cylinders, then exposed to the chemical agent, then transferred to a growth medium Evaluating effectiveness of disinfectants and antiseptics • 4) In-use test- a technique for monitoring the correct use of disinfectants in a clinical setting • involves placing used, diluted disinfectant onto an agar plate to see if microbial colonies will grow • can determine whether disinfectant solutions are being used correctly in clinical settings • Example: floor is swabbed before and after application Figure 13.32 • Used disinfectant solutions in a clinical setting can be checked with the in-use test for contamination with microbes.