Chapter 7: The Control Of Microbial Growth Flashcards
Importance of Ignaz Semmelweis
-discovered the cause of puerperal fever and introduced antisepsis into medical practice
-handwashing protocols reduced the maternal death rate
Joseph lister
helped introduce germ theory and laid the foundation for the use of antiseptics in the practice of medicine and surgery
Sterilization
-Removal of all microbial life, including endospores (Bacillus and Clostridium)
-usually use steam under pressure or a sterilizing gas
Commercial sterilization
-process that uses heat to destroy microorganisms and pathogens in food, making it safe to eat for longer
-killing Clostridium botulinum (oval-shaped, heat-resistant spores that allow the bacteria to survive in unfavorable conditions) endospores (When conditions are favorable, the endospores germinate and produce the botulinum neurotoxin, which causes botulism)
-more resistant endospores may survive but will not germinate
-sanitization for eating utensils
Disinfection
-Rem of vegetative or non-endosporeforming pathogens
-alcohol, chlorine and chlorine compounds, formaldehyde, glutaraldehyde, hydrogen peroxide, iodophors
-use physical or chemical methods on inert surfaces
Antisepsis
-Destruction of vegetative pathogens on living tissue
-does not destroy vegetative pathogens on inert objects
-chemical antimicrobials is applied skin or living tissue
Degerming
-Rem of microbes from a limited area, such as skin
-usually, mechanical rem by soap and water or an alcohol-soaked swab
-using antiseptic to remove vegetative organisms
Sanitization
-Lower microbial counts on eating and drinking utensils
-high-temp washing or dipping into chemical disinfectant
Factors influencing effectiveness of antimicrobials
1) # of microbes
2) microbial characteristics
-endospore-forming bacteria
-Mycobacteria have a waxy, lipid cell wall
-cysts of Protozoa are resistant to chemical disinfection
-gram-(-) bacteria are more resistant (ex. Pseudomonas aeruginosa)
-enveloped vs. non-enveloped viruses
Prions are resistant to normal autoclaving and disinfection
3) environment (organic matter, temp./pH, and biofilms- Pseudomonas, S. epidermis)
4) time of exposure
5) action of antimicrobial
-alteration of plasma membrane permeability
-damage protein or nucleic acid
Microbial load
-number and type of microorganisms in a given area or on a specific object or organism. It can be used to measure the quality of food and water, and to assess the risk of infection in a patient.
-higher the load pop. you must ⬆️ exposure time
Characteristics of microbes: most resistance- least resistant
-prions
-endospores of bacteria
-mycobacteria
-cysts of Protozoa
-vegetative Protozoa
-gram-(-) bacteria
-fungi, including most fungal spores
-viruses w/o envelopes
-gram-(+) bacteria
-viruses w/ lipid envelopes
Moist heat sterilization: Autoclave
-Denatures proteins 121 degrees Celsius, 15psi, 15min
-does not eliminate prions
-steam under pressure
-wrap w/ cloth or paper (not foil)
Moist heat: boiling
-moist heat sterilization, 100 degrees Celsius, kills most vegetative pathogens and almost all viruses in 10min
-some endospores can resist boiling > 20hrs
-used for cooking
Dry heat sterilization
-Kills by oxidation (loss of e-‘s and molecules of organism)
1) flaming
2) incineration- can NOT be used to sterilize heat is protein denaturation; can be used for mad cow disease
3) hot-air sterilization (170 degrees Celsius, 2hrs)
-hot oven: sterilizing materials that cannot tolerate moisture, such as glassware, metal instruments, powders, oils, and other anhydrous substances, as well as for drying samples in laboratory settings
Equivalent treatments: Autoclave vs. hot-air
Autoclave: 121 degrees Celsius, 15 min
Hot-air: 170 degrees Celsius, 2 hrs
Methods of sterilization: gaseous chemosterilant
-chemical that sterilizes a closed environment or system using gas. Chemosterilants can be used to control pests or sterilize medical devices
-➖cellular activity
-eliminate endospores and mycobacterium
-denature proteins
-ex. ethylene oxide- potential carcinogen
-used for sterilizing hear-sensitive items
-ex. Mattress, pillow cases, catheter
Methods of sterilization: filtration
-Membrane filtration rem’s microbes >0.22micrometers (0.2-0.45micrometers)
-when dealing with heat-sensitive liquids or solutions that would be damaged by other sterilization methods like heat, radiation, or strong chemicals, such as certain protein solutions, certain cultured media, enzymes, vaccines, or delicate biological samples, where preserving the integrity of the liquid is crucial
-HEPA (high effect particulate air filters) rem’s microbes >0.3micrometers
-where is this used?
-OR, burn units, rooms of AIDs pt and TB pt’s
-Mycobacterium TB, Legionella, viruses, and mold and fungal spores
-used when sterilizing heat-sensitive liquid
-filter: pores in nitrocellulose acetate membrane
-end result: sterile filtrate
Methods of sterilization: radiation
-damages nucleic acid
-both can be used to damage the microbe’s DNA for sterilization purposes
-ionizing radiation (gamma, x-rays): breaks DNA
-food- kills E. coli and salmonella
-nonionizing radiation (UV): thymine dimers
-UV (germicidal) lab- used in nurseries
Antiseptic
substance that inhibits or kills microorganisms on living tissue. It is used to prevent or treat infections.
Removes vegetative organisms
Physical control: nonsterilizing
-osmotic pressure causes plasmolysis
-creates hypertonic environment
-will not eliminate endospores
-used in preservation of foods such as jams and jellies
-chemical food preservatives: organic acids- sorbic acid and benzoic acid ➖ growth of molds in foods and cosmetics
Cold methods of microbial control
-⬇️ chemical reactions in microbes- slow down growth
-food, cultures, reagents, antibiotics (short-term), drugs
1) refrigeration (bacteriostatic- ➖growth of bacteria)
2) deep-freezing (-50 degrees Celsius- -95 degrees Celsius for preservation of microbes)
-bacterial cultures (long term), antibiotics(long term), drugs, foods
3) lyophilization (-54–72 degrees Celsius for preservation
Pasteurization: nonsterilizing
-pasteurization reduces spoilage of organisms
-eliminates vegetative pathogens
-Salmonella, Listeria, E.coli
-high-temp. Short-time (HTST) 72 degrees Celsius for 15sec
-used to extend the shelf life of food and make it safer to eat. It’s commonly used for dairy products, fruit juices, alcoholic beverages and canned foods
-eliminates non-endosporeforming pathogens
-many heat-resistant bacteria survive but these are not likely to cause disease or cause refrigerated milk to spoil
Principles of effective disinfection
selecting the appropriate disinfectant based on the type of microorganism, ensuring proper concentration and contact time, thoroughly cleaning surfaces before disinfection, addressing organic matter that can interfere with disinfectant action, considering the surface type, and following safety guidelines when handling disinfectants
-careful attention should be paid to the properties and concentration of the disinfectant to be used by reading the manufacturer’s label
-the presence of organic matter, degree of contact w/ microorganisms, and temp should also be considered
Types of disinfectants
Surface-active agents (molecules that are attracted to both water and oil) or surfactants
-⬇️ surface tension among molecules
1) soap and water- mechanical rem by scrubbing
-skin degerming
2)Quaternary ammonium compounds Cationic detergent (QUATS)- denatures proteins or enzymes and injure plasma membranes
-used as disinfectant or as an antiseptic
-low level disinfection
-bacteria ideal for gram-(+) bacteria
-Pseudomonas, Mycobacteria and Naked viruses, endospores are resistant
