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CONTROLLING MICROBIAL GROWTH IN THE ENVIRONMENT - Coggle Diagram
CONTROLLING MICROBIAL GROWTH IN THE ENVIRONMENT
PHYSICAL METHODS
exposure to extreme cold:
decreases microbial metabolism, growth, and reproduction
; psychrophilic microbes can multiply in refrigerated foods
freezing: slow freezing more effective than quick freezing; organisms vary in susceptibility to freezing
refrigeration: halts growth of most pathogens
desiccation: (
drying
) inhibits growth due to removal of water; only microbiostatic
exposure to extreme heat:
high temp denatures proteins, interferes with cytoplasmic membrane/cell wall, and disrupts structure & function of nucleic acids
; thermal death point is lowest temp that kills all cells; thermal death time is time to sterilize vol of liquid at set temp
dry heat:
used for materials that cannot be sterilized by moist heat; denatures proteins and oxidizes metabolic chemicals;
requires higher temp for longer time
incineration: ultimates means of sterilization
moist heat:
used to disinfect, sanitize, & sterilize; kills by denature proteins and destroying cytoplasmic membrane
; more effective than dry heat, water is better conductor of heat than air
autoclaving: pressure applied to boiling water prevents steam escaping; boiling temp increases as pressure increases
pasteurization: used for milk, ice cream, yogurt, etc.; not sterilization, heat-tolerant/loving microbes survive
flash pasteurization: 72°C for 15 sec
ultrahigh-temp pasteurization: 134°C for 1 min
batch method: 30 mins at 63°C
boiling:
kills vegetative cells of bacteria, fungi, protozoan trophozoites, and most viruses within 10 mins
; water boils at lower temperature & requires longer boiling time
ultrahigh-temp sterilization: 140°C for 1 sec, then rapid cooling; treated liquids can be stored at room temp
osmotic pressure:
high concentrations of salt or sugar in foods to inhibit growth
; water in cell is drawn out by osmosis and cell desiccates; fungi have ability to survive hypertonic environments
filtration:
the passage of air or a liquid through a material that traps and removes microbes
membrane filter: have pores small enough to trap the smallest viruses, and even some large proteins
HEPA: (high-efficiency particulate air) filters remove microbes and particles from air
radiation:
shorter wavelengths equals more energy and greater penetration
; describes according to effects on cellular chemicals:
ionizing radiation:
wavelengths shorter than 1 nm; create ions by ejecting electrons from atoms
; ions disrupt hydrogen bonding, oxidize double covalent bonds, and create hydroxide ions; hydroxide ions denature DNA molecules
gamma rays: penetrate well but require hours to kill microbes;
used to sterilize meats, spices, fresh fruit, & vegetables
x-rays: require too much time to be practical
electron beams: effective at killing but do not penetrate well;
used to sterilize sliced meats, microbiological plastic, medical & dental supplies
non-ionizing radiation:
wavelengths greater than 1 nm; excites electrons and causes them to make new covalent bonds
; affects 3-D structure of proteins/nucleic acids
UV light: causes thymine dimer in DNA; does not penetrate well;
suitable for disinfecting air, transparent fluids, and object surfaces
lyophilization: (
freeze-drying
) preserves microbes and other cells for years; used for long-term preservation of microbial cultures; prevents formation of damaging ice crystals
CHEMICAL METHODS:
affect microbes cell walls, cytoplasmic membranes, proteins, DNA
; tend to be more effective against enveloped viruses, bacteria, fungi, and protozoa
surfactants: surface chemicals that reduce surface tension of solvent to make them more effective at dissolving solutes
quats:
low-level disinfectants
; colorless, tasteless, harmless to humans, and antimicrobial; ideal for medical and industrial use
soaps: hydrophilic & hydrophobic ends; good degerming agents but not antimicrobial
detergents: positively charged organic surfactants
heavy metals:
low-level bacteriostatic/fungistatic antimicrobial agents
; inhibit or eliminate protein function by altering the 3-D shape
thimerosal: used to preserve vaccines
copper: controls algal growth in reservoirs, fish tanks, swimming pool, and water storage tanks by interfering with chlorophyll
1% silver nitrate: used to prevent blindness caused by
N. gonorrhoeae
oxidizing agents:
high-level disinfectants and antiseptics
; kill by oxidizing microbial enzymes
peracetic acid: effective sporocide used to sterilize equipment
ozone: treatment for drinking water
hydrogen peroxide: disinfect & sterilize surfaces of objects; catalase neutralizes, not useful for open wounds
aldehydes: denatures proteins and inactivates nucleic acids by cross-linking -CHO groups with amino, hydroxyl, sulfhydryl, and carboxyl groups
glutaraldehyde:
disinfects (short exposure) & sterilizes (long exposure)
formalin: used in embalming and to disinfect rooms & instruments
halogens:
intermediate-level antimicrobial
; damages enzymes via oxidation or denaturation; treatment of drinking water, bleach, used in wound dressing, bromine disinfection
gaseous agents: used to sterilize items; denatures proteins and DNA by cross-linking functional groups; used in hospitals and dental offices
alcohols:
intermediate-level disinfectant
; denatures proteins & disrupts cytoplasmic membranes; used to swab skin before injection
antimicrobics: antibiotics, semisynthetic, and synthetic chemicals; used to treat disease; can be used for antimicrobial control outside the body
phenols:
intermediate- to low-level disinfectant
; denatures proteins and disrupts cell membranes; effective in organic matter and for a prolonged time; used in labs, home, heathcare
SELECTION OF CONTROL METHODS:
agents should be inexpensive, fast-acting, stable during storage, and control all microbial growth while being harmless to host
factors affecting the efficacy of antimicrobials:
nature of site being treated: harsh chemicals and extreme heat cannot be used on humans, animals, & fragile objects; level of control based on site of medical procedure
environmental conditions: temperature and pH
degree of susceptibility of microbes involved: effectiveness of germicides classified:
intermediate-level: kills fungal spores, protozoan cysts, viruses, and pathogenic bacteria
low-level: germicides; kills vegetative bacteria, fungi, protozoa, and some viruses
high-level: kills all pathogens, including endospores
methods for evaluating disinfectants and antiseptics:
use-dilution test: metal cylinders into broth cultures; each are immersed into a different dilution of the disinfectant; the cylinders are removed and incubated; the most effective agent entirely prevents microbial growth with the highest dilutions
Kelsey-Sykes capacity test:
determines the capacity of a chemical to inhibit growth
; chemicals are added to broth cultures, and the turbidity is measures after 48 hours of incubation
phenol coefficient: evaluating the efficacy of disinfectants and antiseptics by determining the ratio of agent's ability to control microbes to that of phenol; greater than 1.0 indicates agent is more effective than phenol
in-use test: swabs taken from objects before and after application of disinfectant or antiseptic; swabs inoculated into medium and incubated; medium monitored for growth
BASIC PRINCIPLES
action of antimicrobial agents:
there are many types of chemical and physical microbial controls
; two basic modes of action
interference with protein and nucleic acid structure
protein:
function depends on 3-D shape
; extreme heat or certain chemicals denature proteins
nucleic acids: chemicals, radiation, and heat can alter/destroy nucleic acids; produces fatal mutants or halts protein synthesis through action on RNA
alteration of cell walls/cytoplasmic membrane
viral envelope:
responsible for attachment of virus to target cell
; damage to envelope interrupts viral replication
non-enveloped viruses have greater tolerance of harsh conditions
cytoplasmic membrane:
contains cytoplasm and controls passage of chemicals into and out of cell
; when damaged, cellular contents leak out
cell wall:
maintains integrity of cell
; when disrupted, cannot prevent cell from bursting from osmotic effects
terminology:
degerming: removal of microbes from a
surface by scrubbing
, whether that surface is human skin or table top
sanitization: process of
disinfecting
places/utensils used by the public to reduce that pathogenic microbes to meet
public
health standards
antiseptic: use of chemicals to inhibit/destroy microorganisms; used on the
skin or other tissue
pasteurization: use of
heat
to kill pathogens and reduce the number of spoilage microorganism in
food and beverages
disinfection: use of physical/chemical agents to
inhibit or destroy microorganism
s; does not guarantee elimination of all pathogens; applies only to treat of
fomites
aseptic: an environment or procedure that is
free of contamination
by pathogens
sterilization: removal or destruction of
all microbes
(including viruses & endospores);
or
the eradication of
harmful microbes
(some microbes may be present)
suffix
-cide/cidal: agents that
destroy
or inactivate a particular microbes
suffix
-stasis/static: agents that
inhibit
the growth of microbes without necessarily killing them