2 - Control of Microbrial Growth (with LE Q's) Flashcards
microorganisms capable of causing disease (pathogens or potential pathogens)
infectious
unwanted microbes i.e. vegetative cells, endospores, protozoan cysts, fungal hyphae, viruses, etc
contaminant
hospital acquired infection
nosocomial infection
clean safe food prep, cleaning dirt/dust; personal hygien
normal household conditions
improved personal hygiene (handwashing); routine use of chemical disinfectants
general medical conditions
assume patients are infectious; use PPE; wash hands etc
Standard precautions
BSL-1
agents NO known potential for infection
BSL-2
clinical samples, including HIV and several more unusualy pathogens (not highly transmissible by respiratory route); PPE, lab access, special handling
BSL-3
more unusual or HIGHLY transmissible i.e. Mycobacterium tuberculossi, Brucella spp., infrequently encountered viruses, mold stages of fungi (highly transmissible respiratory. Precautions include Level 2 precautions HEPA filter mask, special lab design for control of air movement
BSL-4
agents highly infectious exotic microbes and toxins for which there is no vaccine or effective treatment requiring MAX containment
free of all microorganisms and their spores i.e. microbes have been destroyed or removed
sterile
use of physical procedures or chemical agents to destroy all microbial forms, including bacterial spores (kill or remove the microbes)
sterilization
procedures or chemical agents to destroy, inhibit, neutralize, or remove AT LEAST most of infect org
disinfect / decontaminate
agent or method (usually chemical) used to carry out disinfection; normally used on inanimate objects (levels of high, intermediate, low effects)
disinfectant agents
chemical agents on skin to eliminate or inhibit microorganisms (mild disinfectant)
antiseptic
-cide, -cidal
kills microbe e.g. bacteria, fungi, viruses (maybe not spores)
destroys spores & vegetative cells
sporicidal
-stat, -static
inhibiting growth (prevent) or multiplication of bacteria, but not killing
applying mild heat to kill, or reduce microbes that spoil food & beverage
pasteurization
free of contaminating or infectious microorg
aseptic
easily altered, decomposed, or destroyed by heat
thermolabile
not easily altered, decomposed or destroyed by heat
thermostable
Overall degree of microbial resistance to killing (most to least)
1) Bacterial Endospores
2) Mycobacteriam
3) Protozoan cysts
4) Non-enveloped small viruses
5) Vegetative bacteria
6) Fungi
7) Enveloped viruses
more resistant to antimicrobial control methods than all other microbial forms
Bacterial endospore
microbes are not killed instantly when exposed to lethal agents, but more dysfunctional and die over time. Vegetative cells die more rapidly than spores
microbial death
which die first… vegetative cells or spores?
vegetative die first
a larger quantity of contaminating microbes requires a longer exposure time to destroy
population size
usually increase chem concentration increase micro-org death. Some agents are more effective at lower concentrations
concentration/Intensity of antimicrobial
the longer a population is exposed to a microbicidal agent, the more organisms are killed
duration of exposure
High temps can inactivate enzymes and denature molecules— chem disinfectants may function better/faster at increased temps.
Strong acids can directly kill microbes; weak acid may enable chemicals to inactivate microbes faster
Temperature and pH
organic matter can protect micro-org from heating and chemical disinfectants
presence of protective or neutralizing matter
Modes of Action of Microbial Control Methods
Damage to cell wall
Disrupt cytoplasmic membrane
Inhibit synthesis of proteins and nucleic acids
Alter function of proteins & nucleic acids
a. Block its synthesis, digest it, or break down its surface b. Examples: antibiotics, lysozyme, detergents
Damage to cells wall
a. Cause loss of membrane integrity and selective permeability
b. Example: detergents (surfactants), heat
Disrupt cytoplasmic membrane
a. Interference with gene translation, thus preventing protein synthesis
b. Examples: antibiotics, radiation, formaldehyde
Inhibit synthesis of proteins and nucleic acids
a. Alter bonds that determine secondary and tertiary structure. Altered structure inactivates or denatures functions of enzymes and nucleic acids.
b. Examples: heat, strong organic solvents, phenolics, metallic ions, antibiotics
Alter function of proteins & nucleic acids
a. Refrigeration – slows metabolism of microbes, but does not kill most microbes. Used for prolonging storage and shelflife of foodstuffs, vaccines, blood, medications, etc.
b. Freezing (especially ultra-low, -70°C) – essentially stops metabolism, but does not kill microbes. Used for long-term storage of microbes and serum.
Cold Temperatures ( Physical Control Method)
Methods of PHYSICAL control of Microorganisms
Cold Temperatures
Heat
Radiation
Filtration
a. Heat kills cells by disrupting cell membrane functions, denaturing proteins, and inactivating nucleic acids.
(1) Cell membranes become more fluid at elevated temperatures, causing them to lose their
selective permeability.
(2) Proteins (e.g. enzymes) and nucleic acids are inactivated by breaking their hydrogen bonds,
which unfolds proteins and separates double-stranded nucleic acids.
b. Limited to heat-resistant materials. Sterilization depends on temperature, duration of heating, and
humidity.
c. Moist heat is more effective than dry heat
(1) Moist heat possesses greater heat energy than dry heat
(2) Boiling doesn’t kill bacterial endospores which may survive hours of boiling.
Heat (Physical Control of micro-org)
___ is more effective than dry heat
Moist heat