Chapter 4: Control of Microorganisms Flashcards
Exposure to risk increases with __
- frequency of handling
- types of organisms encountered
- level of contact with the agent
Sterilization:
Destruction of all forms of life, all or nothing process
Disinfection:
Elimination of a defined scoped of microorganisms
Disinfectant:
Chemical agent applied to inanimate objects
Antiseptic:
Substance applied to the skin to the number of bacteria present
Factors that influence the degree of killing:
- Types of organisms
- Number of organisms
- Concentration of disinfecting agent
- Presence of organic material
- Nature (composition) of surface to be disinfected
- Contact time
- Temperature
- pH
- Biofilms
- Compatibility of disinfectants and sterilants
Most resistant to least resistant microbes:
Prions:
– Most resistant infectious agent, has special methods for sterilization
– Naked pieces of protein without nucleic acids
– Transmitted through contaminated products
* Medical products
* Theraputic devices
* Body fluids
* Food products
Endospores:
Coats rich in proteins, lipids, and carbohydrates with
cores containing dipicolinic acid and calcium
* Make it very resistance to treatments
Mycobacterial cell walls:
Lipid rich (mycolic acids)
Enveloped viruses:
Lipid envelope can make them more susceptible
Concentration of disinfecting agents:
Too concentrated or too dilute is not effective
Biofilms:
Protection by microbes living in communities
Presence of organic material will ___
Inactivate chemical agents, prevent interaction between chemical and microbes
Contact time:
– Length of exposure of agent to object
– Nature of microorganism can affect time required
– Sterilize or Disinfection
Temperature affect:
– Low temp. can slow chemical reactions, increasing killing
time
– Generally, the higher the temperature, the better the killing
pH affect:
High or low pH can inactivate agent.
Critical material:
Those that enter sterile or vascular system, must be sterile with no spores
Semi-critical material:
Contact with mucous membrane, high level disinfection, tuberculocidal
Noncritical material:
Contact with intact skin, intermediate-low disinfection
Heat method:
Most common. Can use moist heat, dry heat, boiling, pasteurization.
Filtration method:
Filters with various pore sizes, for bacteria/mold/yeast larger than 0.45 µm
Radiation method:
Ionizing: short wavelength and high energy, high penetrance, Gamma rays
Nonionizing: long wavelength and low energy (low penetrance), UV is good for surfaces
Chemosterilizers:
Kills by:
1. reaction with components of cytoplasmic membrane
2. denaturation of cell proteins
3. reaction with thiol groups of enzymes
4. damage of RNA and DNA
Most common alcohol types of disinfection:
Ethyl alcohol and isopropyl alcohol
Alcohol as a disinfectant:
- Broad spectrum but not sporicidal
- Inactivated by organic material
- Work by denaturing proteins and dissolving lipids (60-90% concentration and must be left to evaporate)
- Good for disinfection of semicritical instruments
Formaldehyde as a disinfectant:
37% aqueous (formalin) or as a gas
- Chemosterilizer in high concentrations
- Carcinogen and irritant
- Not tuberculocidal
- Not recommended on a routine basis
Glutaraldehyde as a disinfectant:
– Alkylation of RNA and DNA via alkylation of sulfhydryl and amino groups
– 2% solution is effective against bacteria, fungi, and viruses
- 10-min exposure between 20-30° C: germicidal
- 3-10 hr exposure is sporicidal at room temp
– Does not penetrate organic material well, but remains active
– Noncorrosive so good sterilizer for medical equipment that is not heat-stable or that can’t be sterilized with gas
Tinctures:
Alcohol and iodine solution used as antiseptic
Iodophor:
Iodine and neutral polymer carrier that increases slow release of iodine (requires free iodine therefore proper dilution is vital)
Povidone-iodine (5-10%):
- Exposure time greater than 30 sec
- Disinfectant only, not sporicidal
- Skin irritant, must be removed from skin after use
Hypochlorite (sodium hypochlorite/bleach):
Pros: Inexpensive and broad-spectrum killing power
Cons:
– Requires long exposure time for sterility
– Corrosive and pH sensitive
– Inactivation by organic matter
– Rapidly degrades (30 days max)
Heavy metals as disinfectants:
- Rarely used due to toxicity and pollution
- Slowly bactericidal, but mainly bacteriostatic (prevent the growth of bacteria)
Silver nitrate:
– Previously used as prophylactically for gonococcal conjunctivitis in newborns. Been replaced by erythromycin drops
Copper and copper alloys: antimicrobials for solid surfaces
* Rails
* Door handles
* Etc.
Detergents: Quaternary Ammonium
Compounds (Quats)
- Cationic, surface-active agents
- Reduced effectiveness in hard water and soap
- Some gram(-) are resistant
- Generally used on noncritical surfaces likes floor or bench tops
Phenols (carbolic acid) are less toxic and more effective when substituted with:
halogens, alkyl, phenyl, or benzyl groups
Phenols as a disinfectant:
– Broad-spectrum activity but not sporocidal (additive to detergents to disinfect)
– Stable and biodegradable
– Active in presence of organic matter
– Disrupt cell walls and precipitate proteins
– Used in disinfection of hospital, institutional, and
household environments at high concentrations
– Antiseptics and soap at low concentrations
Phenol: Chlorhexidine gluconate (CHG):
– Used as topical antiseptic
– Disrupts microbial cell membrane
– Precipitates cell contents
– Broad spectrum and effects can last for 6 hours on the skin
– Not generally effective against bacterial spores and nonenveloped viruses
– Considered safe and non-toxic
– Can cause severe skin reactions in infants under 2 months of age
– Sensitive to pH (optimal range is pH 5.5-7.0)
– Hands of surgical personal and whole body of patients undergoing surgery
Phenols: Hexachlorophene (3%)
– Primarily effective against gram-positive bacteria
– Interrupts bacterial electron transport
– Quick effectiveness (15-30 sec), longer for gram-negative organisms when effective
– Residual activity for several hours and cumulative
effect when used as topical antiseptic
– Prescription only due to toxic effects
Phenols: Chloroxylenol (0.5-4%)
– Halogen-substituted phenolic compound
– Used primarily against gram-positive bacteria
– Primarily in skin applications (handwash and surgical scrub)
– Unaffected by organics
– Neutralized by nonionic surfactants and
polyethylene glycol (PEG)
– Minimally persistent
Ethylene oxide as disinfectant:
Best for plastics and heat sensitive material.
- Explosive hazard when mixed with NO2 or CO2
- 450-700 ng per liter of space at 55-60 celsius for 2 hours with humidity at 30%
- Kills through alkylation of nucleic acids
Vaporized hydrogen peroxide (H2O2) and
Periacetic acid:
– Sterilant in pharmaceutical and medical device manufacturing
– Both are bactericidal, fungicidal, and sporicidal.
– When used together contact time required is shortened.
FDA Regulations on Chemical Skin
Antiseptics:
New drug application (NDA): recognized as safe and effective, usually initially approved for prescription use only
Over the counter drug review: monograph, generally recognized as safe and effective, 3 categories
Goal of handwashing:
– Eliminate transient microbiota
– Protect the skin with resident microbiota (leave these behind)
– Prevent transmitting infections
May use waterless liquid or gel if __
no visible soiling
Presurgical Skin Disinfection:
Goal to degerm an intended surgical site rapidly and provide a high level of inactivation for up to 6 hours
Points to remember PART 1:
- Physical and chemical methods may be used in the process of sterilization to remove all forms of life.
- Disinfection involves removal of pathogenic organisms but may not include removal of bacterial or other spores; most disinfectants are chemical agents.
- Factors that influence the degree of killing include types of organisms, number of organisms present, concentration of disinfecting agent, amount of soil present, and nature of the surface to be disinfected.
- Antiseptics are designed to reduce the bacterial load of living tissues.
- Disinfectants are designed to be used on inanimate objects to kill or destroy disease-producing microorganisms.
- Antimicrobial agents for health care personnel use must meet certain standards that demonstrate the product’s safety and efficacy.
Occupational Safety and Health Administration (OSHA):
– Safety training for potentially exposed employees
– Goal is to protect workers
1991 bloodborne pathogen final standard was revised in 2001 in conformance with Needlestick Safety and Prevention Act
Exposure control plan that is required by OSHA:
- Determine tasks that may result in occupational hazards
- A plan to investigate exposure and prevent reoccurrences
- Methods of compliance with universal precautions
- Engineering and work practice controls
- Personal protective equipment (PPE)
- Guidelines for workplace cleanliness
- Guidelines for handling and disposal of regulated waste
- A training program for all employees
Universal (bloodborne) and Standard (all)
precautions:
Developed in 1985, revised in 1996
Standard: all blood and body fluids are treated as infectious (exception is sweat)
Precautions: handwashing, gloves, masks, face shield, lab coats, sharps disposal, environmental controls
Transmission-based precautions:
Added precautions that are used when the patient is known to be or suspected of being infected or colonized with an infectious agent that requires extra measures to prevent spread or transmission of the agent
Microbes for contact precautions:
MRSA, Clostridioides difficile
Microbes for droplet precautions:
Neisseria meningitides, Bordetella pertussis,
influenza, SARS-CoV-2 (COVID-19)
Microbes for airborne precautions:
Mycobacterium tuberculosis, varicella-zoster virus
Engineering Controls:
Controls designed to isolate or remove hazards from the workplace, like eye wash stations, safety showers, eye shields
In labs: negative air pressure, limited access, insect prevention
Work Practice Controls:
- No mouth pipetting
- No eating, drinking, smoking, or applying cosmetics in the laboratory
- Disinfecting workstations at the end of each shift and after any spill of infectious material
- No recapping or breaking of contaminated needles
- Disposal of needles in puncture-resistant containers
- Procedures minimize splashing and the generation of air droplets
- Specimens transported in containers with secure
ilds (prevent leakage of infectious materials) - Frequent handwashing
BSL-1
– Well classified and not normally causing disease in
healthy adult
– Standard PPE and no BSC needed
– See text for guideline list
BSL-2
– Moderate potential hazard
– PPE and BSC class II when aerosols or splashes
possible
– See text for guideline list
BSL-3
– Potential aerosol transmission
– Agents may have serious lethal consequences
– PPE, BSC Class II or III, negative-pressure rooms
– See text for guideline list
BSL-4
– Dangerous and exotic pathogens
– 2 types: cabinet and suit
– PPE, BSC Class III, negative-pressure rooms
– Decontamination of room and personnel after use
– See text for guideline list
Points to remember PART 2:
- Major sources of biological hazards come from patient samples during processing and handling of actively growing culture materials.
- Protective equipment should be used appropriately.
- Safety policies and procedures should always be followed.
- The microbiology safety program includes proper and safe disposal of infectious waste material.
- OSHA regulations for blood-borne pathogen protection should be followed.
- Chemical and fire safety hazards must be identified, and measures to prevent chemical spills should be employed.
- Continuing education programs to train laboratory personnel in all aspects of laboratory safety and exposure control should be in place.
