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
Quaternary Ammonium Compounds (QUATS)
-most effective against gram-(+) bacteria
-Staphylococcus, Streptococcus
-ineffective against endospores Mycobacterium (Clostridium, Bacillus), and Pseudomonas aeruginosa (gram-(-) bacteria- rods, porins, forms biofilms)
-Norovirus, rhinovirus
-antiseptic (on living tissue) and disinfectant (medical equipment)
-ex. Cepacol- for sore throat med and mouthwash
-protein denaturation
-gram-(-) bacteria (Pseudomonas aurigrnosa- forms biofilms) is resistant (to cations detergents and disinfectants)
-disrupts plasma membrane
Alcohols
Ethanol and isopropanol
-(purell hand sanitizers): 60-95%
-denaturation requires water (can’t act on proteins until diluted w/ water-activates)
-modes of action: Denatures proteins or enzymes and injures plasma membranes.
-Used as a disinfectant (cleaning medical equipment- stethoscope, thermometer) or antiseptic (skin degerming- alcohol wipe)
-Not effective against endospores or Naked viruses.
-skin degerming
-cannot eliminate endospores
Halogens
-iodine and chlorine
-I-: betadine- skin degerming
-Cl-: water disinfectant, bleach (Clorox), eliminate endospores
-oxidizing agents, ➖ protein function, alter cell membranes
-effective against most bacteria, many endospores, various fungi, and some viruses- enveloped
-iodine available as a tincture and iodophor
-denatures proteins or enzymes and injure plasma membranes and Oxidizing Agent
-Pseudomonas and cysts of parasites are resistant
Biguanides
-Chlorhexidine
-disrupts plasma membranes affecting selective permeability (mode of action); bactericidal (ability or kill bacteria)
-skin antiseptics, especially for surgical scrubs and prepoperative skin prep
-nontoxic
-viral for most bacteria including Mycobacteria and enveloped viruses
-not effective against endospores or Pseudomonas
Phenol (derivatives)
-disrupts the cell wall of a microbe, resulting in the bursting open of the cell and eventually the lysis of the cell. As a result, they poison the entire protoplasm. These two mechanisms of action of phenol together result in the death of the bacteria on the objects.
-lysol and amphyl- disinfectants
-denatures proteins and dirupts plasma membrane
-preferred uses:
-disinfection- benchtop, equipment
-activity against Mycobacterium- most bacteria except endospores
Aldehydes
-inactive or denature proteins
-Glutardehyde (Cidex) sterilant
-endosporicidal in 3-10hrs (exposure time)
-formaldehyde (g)- embalming
-formalin
-preserve tissue
-sterilize medical equipment
-sterililant very effective against endospores, Mycobacteria, and viruses
-Oligodynamic Action (combines w/ sulfhydryl groups to denature proteins
-not effective against endospores or Mycobacteria
-carcinogens
Heavy metal
-Oligodynamic action-➖ growth of microbes
-combines w/ sulfhydryl groups denatures proteins in microbes
-ex.
-silver nitrate
-gtts- prevents Neonatal gonorrheal ophthalmia- could lead to blindness (erythromycin used in replacement in more recent yrs)
-mercurochrome-discontinued
-copper sulfate-tablets of copper sulfates to disinfect water, kill algae and bacteria
-not effective against endospores or Mycobacterium
Peroxygens
-oxidizing agents
- (3%) Hydrogen peroxide
-used as an antiseptic (wound-catalase (enzyme on skin)- breaks down H2O2) or disinfectant- cleaning cl’s
-does not eliminate endospores
-Pseudomonas may be resistant
Evaluation of a disinfectant: filter paper disk diffusion method
1) a paper disk is soaked w/ inoculated w/ disinfectant and is placed on an inoculated agar plate
2) the disinfectant diffuses out of disk into agar during incubation
3) a clear zone of inhibition indicates effectiveness of the disinfectant for a given bacteria
-24hrs, 37 degrees celcius in air
-gram-(+) bacteria is most susceptible to
Prions
-Most resistant
-not cellular, infectious proteins
-cause mad cow disease
-cannot use autoclave, must incinerate
Endospores
-2nd most resistant
-have to sterilize
-ex. Bacillus and Clostridium are bacteria that can form endospores
Mycobacteria
-3rd most resistant
-waxy lipid cell wall (mycolic acid)
-amphyl or Lysol (phenolics) can eliminate
Cysts of protozoa
-4th most resistant
-ex. Giardia- diarrhea
-resistant to chemical methods of microbial control
Gram-(-) bacteria
-5th most resistant
-prions in cell wall- can close and chemicals can’t enter
-ex. Pseudomonas form biofilms
Fungi
-6th most resistant
Viruses w/o envelopes
-7th most resistant
-norovirus and rhinovirus
Gram-(+) bacteria
-8th most resistant
Viruses w/ envelopes
-9th most resistant
-envelopes= lipid covering
-HIV, HBV/HCV in blood
-use bleach to eliminate
Preferred uses of an autoclave
-microbial media
-live bacterial cultures
-linens, dressings, utensils, and equipment
Direct flaming
-buses burner sterilizes metal wire loops- turns bright orange
-also sterilize lip of test tube
-allow to cool
In what situations is filtration the only practical way to eliminate undesirable microbes
-antibiotic solutions
-vaccines
-cultured media (cell culture)
-IV saline/glucose solutions- maintains electrolytes
Methods of sterilization: ionizing radiation
-used to sterilize heart-sensitive objects
-damages nucleic acid
-for food- meat, eggs- E. coli and Salmonella
Ionizing radiation
-gamma and x-rays
-breaks DNA
-highly penetrating- wear a shield
-medical equipment, vaccines, food
-anthrax on mail
Non-ionizing radiation
-UV rays
-thymine dimers: two adjacent thymine bases in DNA that are abnormally linked by covalent bonds due to UV radiation. They form a stiff kink in the DNA structure, which can prevent replication and transcription
-less penetrating, protect eyes and skin
-UV (germicidal) lamp
Chemical food preservative- nonsterilizing
-organic acid- sorbic and benzoic acid ➖ growth of molds or bacteria in food and cosmetics
-will not eliminate endospores
-mechanism of action: metabolic inhibition
Glutaraldehyde: effectiveness of chemical antimicrobials
-effect against endospores: fair
-effect against mycobacteria: good
Chlorines: effectiveness of chemical antimicrobials
-effect against endospores: fair
-effect against mycobacteria: fair
Alcohols: effectiveness of chemical microbial
-Effect against endospores: poor
-effect against mycobacteria: good
-exert effects on membrane lipids and on proteins (effect selective permeability- mode of action) resulting in denaturation (mode of action)
Iodine: effectiveness of antimicrobials
-effect against endospores: poor
-effect against mycobacteria: good
Phenolics: effectiveness of chemical antimicrobials
-effect against endospores: poor
-effect against mycobacteria: good
Chlorhexidine: effectiveness of chemical antimicrobials
-effect against endospores: none
-effect against mycobacteria: fair
-injures plasma membrane
Bisphenols
-effect against endospores: none
-effect against mycobacteria: none
QUATS: effectiveness of chemical antimicrobials
-effect against endospores: none
-effect against mycobacteria: none
Silver: effectiveness of chemical antimicrobials
-effect against endospores: none
-effect against mycobacteria: none
Norovirus (Norwalk virus)
-RNA, non-enveloped virus causes gastroenteritis- diarrhea
-is not killed my QUATS
-fecal-oral routes from water, food
-dx: stool polymerase chain reaction (PCR)- detect nucleic acid of virus in stool
-oral rehydration- replace fluids and electrolytes lost in diarrhea
Types of disinfectants
-surface-active agents or surfactants
-soap (regular)- Quaternary ammonium compounds (QUATS) Cationic detergents
-degerming- denatures proteins, disrupt plasma membrane
-limited germicidal action-routine hand washing
Halogen: iodine
-antiseptic; disinfectant of water
-available as a tincture (iodine in 70% alcohol) and iodophor (iodine plus organic substance)
-betadine: surgical scrub brushes and skin-degerming
Halogens: Chlorine
-preferred uses:
-water disinfectant
-can become resistant to chlorine: Crytosporidium, parasites, giardia cysts, Pseudomonas aeruginosa (swimmer’s ear)
-Hypochlorous acid (Sodium hydrochloride- Clorox)- 1:10 dilution
-bleach for blood spill- HIV
-1L of water and 10 drops of bleach- 30min- safe to drink
Bisphenol: hexachlorophene
-skin antiseptic and surgical scrubs
-ex. Phisohex
-nurseries out break of impetigo Staphylococcus aureus or Streptococcus
-endospores , Mycobacteria , Pseudomonas and cysts of Protozoa are resistant
Bisphenol: Triclosan
-mouthwash, toothpaste- prevent dental plaque, and antibacterial soaps (discontinued in 2016)
-leakage in the environment
Antibacterial soap: doing more harm than good?
-overuse of antimicrobial chemicals like triclosan might also be contributing to antibiotic resistance in bacteria
-ex. Staphylococcus aureus
Norovirus (Norwalk virus)
-RNA, naked virus causes gastroenteritis
-fecal-oral routes from water, food
-dx: stool Polymerase Chain Reaction (PCR)-detect nucleic acid of virus in stool
-oral rehydration-replace fluids and electrolytes lost during diarrhea
Antiseptic
substance that kills or inhibits the growth of microorganisms on living tissue
Cidal
Having the power to kill bacteria
What is the difference between sterilization and disinfection?
Sterilization is a chemical or physical process resulting in the destruction of all living organisms. Disinfection can be a physical or chemical method that reduces the number of viable cells.
Methods of sterilization
-Direct flame (incineration)
-autoclave (steam under pressure), -chemical sterilization (ethylene oxide EtO)
-filtration
-ionizing radiation
Is non-ionizing radiation an example of sterilization?
can be used for sterilization, but it is typically only effective for surface disinfection or superficial sterilization due to its low penetration power, unlike ionizing radiation which is more commonly used for full sterilization of medical devices and other materials
-cide
Killing
Biocide/germicide
-static
Stop
Bacteriostatic- substances that inhibit the growth and multiplication of bacteria without necessarily killing them
What is resistant to Bisphenols?
Endospores, Mycobacteria, Pseudomonas and Cysts of Protozoa
Hydrogen peroxide
-mode of action: oxidation
-used as an antiseptic (wound cleaning, etc.) or as a disinfectant (cl’s cleaning, etc.)
-catalase enzyme in human cells break down hydrogen peroxide when used as an antiseptic
Desiccation
Disrupts the microbe’s metabolism by depriving the organism of water needed for growth
Chemical methods of microbial control include:
Disinfectants and antiseptics
