Microbial Control Methods & Disinfection

Microbial Control Methods Overview

• Physical agents, chemical agents, and mechanical removal methods are all microbial control methods
• Physical agents include heat and radiation
• Chemical agents include gases and liquids
• Mechanical removal methods involve filtration of air and liquids
• Disinfection destroys or removes Vegetative pathogens (refer to the active, growing forms of microorganisms that can cause disease), but not bacterial endospores, and is used on inanimate objects
• Sterilization completely removes or destroys all viable microorganisms on inanimate objects
• Antiseptics are chemicals applied to body surfaces to destroy or inhibit vegetative pathogens

Disinfection Explained

• Disinfection is a physical or chemical means of killing microorganisms, but not necessarily spores
• A disinfectant is a chemical or mixture used to kill microorganisms, but not necessarily spores
• Disinfectants are generally applied to inanimate surfaces or objects

Properties of an Ideal Disinfectant/Preservative

• Broad spectrum of activity is necessary
• High potency under conditions is an important consideration
• It is crucial that a disinfectant or preservative does not negatively impact the integrity or appearance of materials such as linen and metals. This ensures that the disinfectant can be used widely without damaging important surfaces or items that require careful maintenance.
• Must have complete compatibility with other agents or components of a formulation and its container
• Should be stable on storage and over a wide pH range
• Should be Economical
• Should be odorless and non staining

Disinfection and Related Terms

• Antiseptics inhibit the growth and development of microorganisms without necessarily killing them; they are applied to body surfaces
• Decontamination involves any process for removing and/or killing microorganisms. This term is also for removing or neutralizing hazardous chemicals and radioactive materials
• Cleaning involves removing dirt, organic matter, and stains that can interfere with the killing action of decontaminants
• Cleaning methods include brushing, vacuuming, dry dusting, and washing or damp mopping with water containing a soap or detergent
• Pre-cleaning is essential for effective disinfection or sterilization
• Pre-cleaning must be done carefully to avoid exposure to infectious agents
• Materials used for pre-cleaning must be chemically compatible with later germicides
• Germicides are powerful agents specifically formulated to kill or inactivate harmful microorganisms, including bacteria, viruses, fungi, and protozoa. They play a crucial role in infection control and public health by reducing the risk of disease transmission. Germicides can be categorized into various types based on their mode of action, spectrum of activity, and chemical composition. Some common categories include disinfectants for surfaces, antiseptics for skin, and sterilants for medical instruments.
• A chemical germicide is versatile and can effectively serve dual purposes, functioning both in the initial pre-cleaning phase to prepare surfaces and in the subsequent disinfection stage to eliminate pathogens effectively.

Chemical Germicides: Safety

• Germicides might be harmful to humans or the environment
• Select, store, handle, use and dispose of them with care
• Gloves, aprons, and eye protection are recommended when mixing chemical germicides

Specific Chemical Germicides

Chlorine

• Fast-acting, broad-spectrum chemical germicide
• Relatively harmless to human tissues, easy to handle, colorless and non-staining
• Normally sold as bleach: an aqueous solution of sodium hypochlorite (NaOCl) that can be diluted with water
• May last for as long as a week
• Requires daily change for solutions receiving materials with high organic matter
• A general all-purpose laboratory disinfectant should contain 0.1% available chlorine
• Biohazardous spillage and in the presence of large amounts of organic matter requires 0.5% available chlorine
• For drinking water disinfection, a final concentration of 1-2 mg/l (1-2 ppm) available chlorine is needed
• Bleach is not recommended as an antiseptic
• Chlorine gas is highly toxic, and the indiscriminate use of bleach is to be avoided

Iodine Iodophors

• Action is similar to chlorine, but slightly less inhibited by organic matter
• Iodine can stain fabrics and environmental surfaces
• Iodophors and tinctures of iodine are good antiseptics
• Povidone-iodine is a reliable and safe surgical scrub/preoperative skin antiseptic
• Organic iodine-based products need storage at 4-10°C to prevent bacteria growth
• Iodine solution, either in water or alcohol, is applied to the skin before surgery
• Also extremely effective against many Protozoans
• Is toxic if concentration is too high
• Tincture of iodine can stain tissue and cause local skin irritation/allergic reactions
• Can be intrinsically contaminated with Burkholderia cepacia & Pseudomonas aerogenosa causing pseudobacteraemia and peritonitis

Glutaraldehyde

• Active against bacteria, spores, fungi, lipid, and nonlipid-containing viruses
• Non-corrosive & faster acting than formaldehyde, though it requires several hours to kill bacterial spores
• A 2% solution needs to be activated (made alkaline)
• Activated solution can be re-used for 1-4 weeks depending on use
• It is crucial to discard solutions when turbidity occurs, as this indicates contamination or degradation, compromising efficacy and safety.
• Glutaraldehyde is toxic and irritates skin/mucous membranes, so contact must be avoided
• Used in a fume-hood/well-ventilated areas
• This means that glutaraldehyde should not be used as a mist or liquid for cleaning surfaces in various environments such as laboratories or healthcare settings.

Cidex-OPA

• Contains O-Phthalaldehyde
• This germicide's formulation allows for immediate use without the need for any preparatory steps, ensuring a more efficient application in various settings.
• Is not known to irritate eyes and nasal passages
• Stability is excellent over a wide range of pH 3-9
• Does not require exposure monitoring
• This characteristic makes it suitable for use in sensitive environments where strong odors could be a concern.
• OPA shows good activity against Mycobacteria, including glutaraldehyde-resistant strains

Phenolic Compounds

• They were the earliest germicides used for environmental surface decontamination
• Active against vegetative bacteria and lipid-containing viruses and fungi
• Activity against mycobacteria
• Are not active against spores
• Activity against non lipid viruses is variable
• Disadvantages include inactivation by water hardness, which consists of dissolved minerals like calcium and magnesium. High hardness levels cause scaling, lower the effectiveness of detergents, and reduce disinfectant efficacy. For phenolic compounds, hardness can diminish antimicrobial properties, necessitating water treatment to ensure optimal performance and compatibility with cationic detergents. Its use is not advised on food contact surfaces.
• May be absorbed by rubber and penetrate the skin

Triclosan

• Bisphenols are organic compounds with two hydroxyphenyl groups, primarily used in plastics and industrial materials. Bisphenol A (BPA), the most recognized, has raised health concerns as an endocrine disruptor affecting hormonal functions in humans and wildlife. Consequently, many countries have restricted BPA in consumer products, particularly food containers. Alternatives like bisphenol S (BPS) and bisphenol F (BPF) are being studied for their safety profiles.
• Common in hand-washing products
• Active against vegetative bacteria and safe for skin/mucous membranes
• Can have anti-inflammatory properties

Dettol

• Is a Halophenol, specifically Chloroxynelol
• Widely used

Chloroxylenol is bactericidal, but P. aeruginosa and many molds are highly resistant

Chlorhexidine

• Is a cationic bisguanide
• 4% solution in a detergent base
• Bactericidal for Gram positive & gram negative bacteria
• Effective against HIV Herpes virus and Influenza virus
• Little affected by blood & other organic materials
• Inactivated by soaps & anionic detergents

Alcohols

• Ethanol (ethyl alcohol) and 2-propanol (isopropyl alcohol) have similar disinfectant properties
• A solution of 70 to 80 percent is employed.
• Concentrations of alcohol above 90 percent and below 50 percent tend to be less effective due to their inability to penetrate the microbial cells effectively, reducing germicidal action.
• Isopropyl alcohol, is effective up to 99 percent
• Leave no residue on surfaces
• A 10-minute exposure kills vegetative cells, but not spores
• Alcohols can be used on skin, work surfaces of laboratory benches/biosafety cabinets, and to soak small pieces of surgical instruments
• Alcohol-based hand-rubs are for decontaminating lightly soiled hands when hand-washing isn't possible
• Precautions: Alcohols are volatile and flammable, use away from open flames
• Proper labeling is essential to prevent accidental autoclaving, which can compromise the integrity of alcohol-containing solutions.

Hydrogen Peracids

• Like chlorine, hydrogen peroxide (H2O2) and peracids are strong oxidants and potent broad-spectrum germicides
• Safer than chlorine to both humans and the environment

Hydrogen Peroxide

• A 3% solution is a harmless but weak antiseptic
• Primarily used to cleanse wounds
• Effective disinfectant on inanimate materials
• Decontaminates work surfaces of laboratory benches and biosafety cabinets
• Stronger solutions disinfect heat-sensitive medical/dental devices
• Vaporized hydrogen peroxide or Peracetic acid decontaminates heat-sensitive medical/surgical devices, but requires specialized plasma sterilizer equipment
• Hydrogen peroxide and Peracids corrode metals like Aluminum, Copper, Brass and Zinc
• Can decolourise fabrics, hair, skin and mucous membranes
• Rinse treated articles thoroughly before contact with eyes/mucous membranes
• Stored away from heat and light

Surface-Active Agents

Detergent substances are divided into 3 groups

Anionic compounds

• Soap
• Sodium and potassium salts
• Alkyl such as sodium lauryl sulfate and alkylbenzenesulfonates

Cationic compounds

• detergents are equally effective against gram-positive and gram-negative bacteria

Quaternary Ammonium Compounds (QAC's)

• Used as mixtures and with added germicides such as alcohols
• Show good activity against vegetative bacteria
• Have an effect on lipid enveloped viruses, including HIV and HBV
• Benzalkonium chloride is used as antiseptics
• The germicidal activity is considerably reduced by organic matter, water hardness and anionic detergents
• Potentially harmful bacteria can grow in quaternary ammonium compound solutions
• Owe to low biodegradability, these compounds may also accumulate in the environment

Spill Clean-Up Procedure

For a Spill of Infectious Material

• Wear gloves and protective clothing, and cover the spill with cloth or paper towels to contain it
• Pour a 5 - 10% bleach solution immediately surrounding area
• Apply disinfectant concentrically beginning at the outer margin of the spill area, working toward the centre
• After 30 minutes, clear away the materials
• Use a dustpan to collect broken glass or sharps and put it in a puncture-resistant container

Decontamination Procedures

• Skin: wash thoroughly with soap and water, while being careful not to damage the skin with detergents or abrasive materials
• Cuts/eyes: irrigate the affected area with water to flush out contaminants, while taking care to avoid spreading the infection to adjacent areas.
• Clothing: remove garments immediately and place in a container. Do not remove them from the spill location until contamination has been monitored

Selection of Appropriate Decontamination

• For most organic matter and bacteria: Use clear soluble phenolics, diluted according to the manufacturers' recommendations
• For blood or viruses use -1% hypochlorites
• Hypochlorite solution is not for use in centrifuges
• Activated gluteraldehyde (2%) is for use on surfaces for decontamination

Local Environmental Decontamination

• Decontaminate the laboratory space, furniture and equipment with sodium hypochlorite containing 1 g/l available chlorine
• Use stronger solutions (5 g/l) for high-risk situations.
• For environmental decontamination, formulated solutions with a concentration of 3% hydrogen peroxide (H2O2) make suitable substitutes for bleach solutions

Fumigation

• Decontaminate rooms and equipment with formaldehyde gas, generated by heating paraformaldehyde or boiling formalin
• Alternately 150gm KMnO4 and 280 ml Formalin per 1000 cu ft area
• Should be conducted at ≥ 21°C and ≥ 70% relative humidity
• After fumigation the area must be ventilated thoroughly before personnel are allowed to enter
• Gaseous ammonium bicarbonate can be used to neutralize the formaldehyde

Choice of Disinfection

• Medical devices, equipment, and surgical materials fall into three categories:

Critical items

• directly contact the bloodstream or normally sterile areas of the body; examples include surgical instruments, cardiac catheters, implants, components of the heart-lung oxygenator, and blood compartment of a hemodialyzer. Sterility is required for these

Semi-critical items

• come into contact with mucous membranes: noninvasive flexible and rigid fiberoptic endoscopes, endotracheal tubes, anesthesia breathing circuits, and cystoscopes. Meticulous physical cleaning followed by an appropriate high-level disinfection is needed

Non-critical items

• either do not touch a patient or only touch intact skin like Crutches, Bed boards, Blood pressure cuffs, and a variety of other medical accessories, items that washing is a detergent is sufficient

Disinfection Policies in Four Main Areas of Usage

• Application to Skin and Mucous Membranes : Phenols, diaguanides, QACs, Iodine preps and alcohols
• Disinfection of instruments or equipment when physical methods cannot be used: alkaline, glutaraldehyde, formaldehyde, phenolics, disaguinides
• Decontamination of potentially contaminated items, e.g. bedpans, urinals, infected surgical equipment: Phenolics, disaguinides, chlorinated cyanurates, hypochlorites/detergents, formaldehyde
• Disinfection on relatively clean surfaces: and Phenolics, disaguinides, hypochlorites, Phenolics

Pharmacists Role

• To ensure disinfectants are properly diluted and freshly prepared
• Disinfectants are used correctly and as directed
• Draw up and maintain protocol for disinfectant use throughout hospital areas