ch 8 control of microorganisms in the environment Flashcards
biocide
all antimicrobial agents that can be used to control microorganisms
can be physical, chemical, mechanical, or biological
sterilization
process by which all living cells, spores, and acellular entities are either destroyed or removed from an object or habitat
sterilant is the chemical agent
disinfection
the killing, inhibition, or removal or microorganisms that may cause disease
- reduction of total microbial population and the destruction of potential pathogens
disinfectants are agents, usually chemical
sanitization
microbial population is reduced to levels that are considered safe by public health standards
antisepsis
the destruction or inhibition of microorganisms on living tissue
prevention of infection or sepsis
antiseptics
chemical agents applied to tissue to prevent infection by killing or inhibiting pathogen growth
chemotherapy
generic term used to describe the application of chemicals to kill or inhibit the growth of microorganisms
cidal agents
substances that kill organisms (not necessarily endospores) that have the suffix -cide
ex. bactericide, fungicides, viricides
static agents
prevent growth (if chemical is removed, growth will resume)
-static
ex. bacteriostatic, fungistatic
D value
decimal reduction time
a measure of an agent’s killing efficiency - time required to kill 90% of the microorganisms or endospores in a sample under specified conditions
physical means to control microbes
filtration
heat
radiation
filtration
way to reduce microbial population in solutions of heat-sensitive material and can be used to sterilize liquids and gases
- depth filter: consist of fibrous or granular materials that have been bonded into a thick layer filled with narrow, twisting channels - microbes removed by entrapment and adsorption to the surface of the filter material
- membrane filter: porous membrane that removes most vegetative cells from liquids
- high-efficiency particulate air (HEPA) filters: N95 masks, exclude 99.97% of particles
heat
damage structures and alter chemical reaction
- boiling will not destroy endospores and does not sterilize
- autoclave: device used in steam sterilization, like a pressure cooker
- pasterization: controlled heating at temps well below boiling, does not sterilize but kills pathogens and slows spoilage by reducing the total load of organisms present
- tyndallization: intermittent sterilization, for materials that cannot withstand the high temps of autoclave
- dry heat sterilization: less effective than moist, oxidizes cell constituents and denatures proteins which causes microbial death, cant be used on heat sensitive materials (plastic) but good for glassware and metal to prevent corrosion
radiation
- UV radiation: causes thymine-thyme dimerization of DNA, preventing replication and transcription, cannot penetrate glass, dirt films
- cold plasma: emits UV radiation and reactive oxygen and/or nitrogen species which damages nucleic acids, and oxidizes nucleic acids, proteins, and lipids
- ionizing radiation: sterilizing agent that penetrates deep into objects, gamma and beta radiation that kills spores, dislodges electrons from atoms or molecules, producing chemically reactive free radicals
phenolics
phenol was the first widely used antiseptic and disinfectant
commonly used as lab and hospital disinfectants
act by denaturing proteins and disrupting cell membranes
tuberculocidal, effective in presence of organic material, and long lasting
alcohols
most widely used disinfectants, antiseptics, and sanitizers
act by denaturing proteins and dissolving membrane lipids
halogens
iodine
- skin antiseptic and kills oxidizing cell constituents and iodinating proteins
- may kill endospores and high concs
- iodophor - water soluble, stale and nonstaining, and release iodine slowly to minimize skin irritation
chlorine
- oxidizes cellular materials and destruction of vegetative bacteria and fungi
- usually death in 30 mins
metals
ions of mercury, silver, arsenic, zinc, and copper were used for many years as germicides - only silver and copper used now
act by inactivating proteins, often via sulfhydryl groups
quaternary ammonium compounds
detergents that have broad-spectrum antimicrobial activity that are effective disinfectants used for decontamination purposes
- detergents: amphipathic organic cleansing agents
kill most bacteria but not M. tuberculosis or endospores
stable and nontoxic but are inactivated by hard water and soap
antimicrobial activity is the result of their ability of disrupt microbial membranes and denature proteins
aldehydes
formaldehyde and glutaraldehyde are highly reactive molecules that inactivate nucleic acids and proteins, probably by cross-linking and alkylating molecules
sporicidal and can be used as chemical sterilants
sterilizing gases
used to sterilize heat-sensitive materials
- microbicidal and sporicidal
ethylene oxide - strong alkylating agent that kills by reacting with DNA and proteins to block replication and enzymatic activity
six factors that affect effectiveness of antimicrobial agents
- population size
- population composition
- concentration or intensity of an antimicrobial agent
- contact time
- temp
- local environment
phenol coefficient test
the potency of a disinfectant compared with that of phenol
useful for initial screening but may be misleading
dilution test
determines rate at which selected bateria are destroyed by various chemical agents
natural control mechanisms of microorganisms
- predation by Bdellovibrio
- bacteriophages
- bacteriocins
- probiotics
