MGY277H1 Study Guide - Final Guide: Non-Ionizing Radiation, Surgical Mesh, Mouthwash
8 Jun 2018
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Unit 6
Overview of Microbial Growth
Principles of Control
- Sterilization: removal or destruction of all microorganisms so they can no longer multiply or
revive
➢ Sterile item is free of microbes including endospores and viruses but does not consider
prions (not destroyed by standard sterilization)
- Disinfection: elimination of most or all pathogens
➢ Some viable microbes may remain
➢ Disinfectants used on inanimate objects
➔ May be called biocides, germicides, bactericides
➢ Antiseptics used on living tissue
- Pasteurization: brief heating to reduce number of spoilage organisms, destroy pathogens
➢ Foods, inanimate objects
- Decontamination: reduce pathogens to levels considered safe to handle
- Sanitization: substantially reduced microbial population that meets accepted health standards
➢ Not a specific level of control
- Preservation: process of delaying spoilage of foods and other perishable products
➢ Adjust conditions to slow microbial growth
➢ Add bacteriostatic preservatives (growth-inhibiting but do not kill)
Situational Considerations
- Microbial control methods depend upon situation and level of control required
Daily Life
- Washing and scrubbing with soaps and detergents achieves routine control
➢ Soap aids in mechanical removal of organisms
➢ Beneficial skin microbiota reside deeper on underlying layers of skin, hair follicles so they
are NOT adversely affected by regular use
➢ Hand washing with soap and water most important step in stopping spread of many
infectious diseases
➢ Other methods include cooking food, cleaning surfaces, and refrigeration
Hospitals and Other Healthcare Facilities
- Minimizing microbial population very important because of the dangers of healthcare-
associated infections – also called nosocomial infections
➢ Patients more susceptible to infection because of weakened condition
➢ May undergo invasive procedures (e.g. surgery), which cuts intact skin that would otherwise
prevent infection
➢ Pathogens more likely to be found in hospital setting because of high concentration of
patients with infectious disease
➔ Feces, urine, respiratory droplets, bodily secretions spread pathogens
➢ Instruments must be sterilized to avoid introducing infection to deep tissues
Microbiology Laboratories
- Routinely work with microbial cultures
- Use rigorous methods to control microorganism growth
- Must eliminate microbial concentration to both experimental samples and environment
➢ Careful treatment both before (sterile media) and after (sterilize cultures, waste)
➢ Aseptic techniques used to prevent contamination of samples, self, laboratory
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- CDC and PHAC guidelines for labs working with microbes
➢ Biosafety levels range from BSL-I (microbes not known to cause disease) to BSL-4 (lethal
pathogens for which no vaccination or treatment exists)
Biosafety Leels also alled Cotaiat Leels
- BSL-4: frequently fatal, no treatments or vaccines, severe issues if released (Ebola, smallpox)
- BSL-3: very dangerous, poor treatment options, respiratory pathogens (TB, SARS, HIV)
- BSL-2: minor hazard, good treatment options, not easily transmitted (Salmonella)
- BSL-1: low hazard, minimal precaution needed (yeast, lab strains of E. coli)
Food and Food Production Facilities
- Perishables retain quality longer when contaminating microbes destroyed, removed, inhibited
➢ Heat treatment most common and reliable mechanism
➔ Can alter flavour, appearance of product
➢ Irradiation approved to treat certain foods
➢ Chemical activities can prevent spoilage
➢ CFIA/FDA regulates use of irradiation and chemical additives because of risk of toxicity
- Facilities must keep surfaces clean and relatively free of microbes to avoid contamination of
large quantities of product
Water Treatment Facilities
- Ensure drinking water free of pathogens
- Chlorine is traditionally used to disinfect water
➢ Saved countless numbers of lives by preventing spread of waterborne illnesses
➢ Can react with naturally occurring chemicals to form disinfection by-products (DPPs), which
have been linked to long-term health risks
- Some organisms resistant to (traditional) chemical disinfectants
➢ Cryptosporidium parvum (causes diarrhea)
➢ Regulations require facilities to minimize DBPs and C. parvum in treated water
Selection of an Antimicrobial Procedure
- Complicated since very method has disadvantages to limit their use
➢ Ideal, multi-purpose, non-toxic method does not exist
- Choice of procedure depends on many factors including:
➢ Type of microbe
➢ Number of contaminating microbes
➢ Environmental condition
➢ Rick for infection
➢ Composition of the item
Types of Microbes
- Products potentially contaminated with highly resistant microbes require more rigorous
treatment
- Bacterial endospores
➢ Most resistant form of life encountered. Only extreme heat or chemicals completely
destroys
➢ E.g. Bacillus, Clostridium sp.
- Protozoan cysts and oocysts
➢ Excreted in feces and cause diarrheal disease if ingested
➢ Resistant to disinfectants but easily destroyed by boiling
➢ E.g. Giardia lambia
- Mycobacterium species
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➢ Waxy cell wall makes resistant to many chemical treatments. Stronger, more toxic chemicals
used to disinfect
- Pseudomonas species
➢ Common environmental organism that can cause serious healthcare-associated infections
➢ Resistant to and can actually grow in some disinfectants
- Naked virus
➢ Lack lipid envelope and more resistant to disinfectants and detergents but still susceptible
to chlorine
➔ E.g. Polio virus
➢ Enveloped viruses (e.g. HIV) are sensitive to these chemicals
Number of Microbes
- Time for heat or chemicals to kill is affected by population size only a fraction of population dies
during given time interval
➢ Large population = more time
- Decimal reduction time: (D value) gauges commercial effectiveness
- Time required to kill 90% of population under specific conditions
Environmental Conditions
- Dirt, grease, body fluids can interfere with heat penetration, action of chemicals
- Another reason why it is so important to thoroughly clean items before disinfection or
sterilization
- pH, temperature can influence effectiveness of microbial death
➢ E.g. sodium hypochlorite (household bleach) solution can kill suspension of M. tuberculosis
at 55 degrees Celsius in half the time as at 50 degrees
➢ Even more effective at low pH
Risk for Infection
- Medical instruments categorized according to risk for transmitting infectious agents – greater
threat, more rigorous procedure
- Critical items come in contact with body tissues
➢ Include needles and scalpels
➢ Must be sterile
- Semi-critical instruments contact mucous membranes but do not penetrate body tissues
➢ Includes endoscopes and endotracheal tubes
➢ Must be free of viruses and vegetative bacteria
➢ Few endospores that remain are blocks by mucous membranes and pose little risk
- Non-critical instruments contact unbroken skin only
➢ Include countertops, stethoscopes, blood pressure cuffs
➢ Low risk of transmission
Physical Methods of Microbial Control
Using Heat to Destroy Microorganisms
- Heat treatment useful for microbial control
➢ Reliable, safe, relatively fast, inexpensive, non-toxic
➢ Can be used to sterilize or disinfect
➢ Methods include moist heat, dry heat
Moist Heat
- Destroys microbes by irreversibly denaturing proteins
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find more resources at oneclass.com
Document Summary
Sterilization: removal or destruction of all microorganisms so they can no longer multiply or revive. Sterile item is free of microbes including endospores and viruses but does not consider prions (not destroyed by standard sterilization) Disinfection: elimination of most or all pathogens. Pasteurization: brief heating to reduce number of spoilage organisms, destroy pathogens. Decontamination: reduce pathogens to levels considered safe to handle. Sanitization: substantially reduced microbial population that meets accepted health standards. Preservation: process of delaying spoilage of foods and other perishable products. Add bacteriostatic preservatives (growth-inhibiting but do not kill) Microbial control methods depend upon situation and level of control required. Washing and scrubbing with soaps and detergents achieves routine control. Soap aids in mechanical removal of organisms. Beneficial skin microbiota reside deeper on underlying layers of skin, hair follicles so they are not adversely affected by regular use. Hand washing with soap and water most important step in stopping spread of many infectious diseases.
