ch 8 control of microorganisms in the environment

Question 1

biocide

Answer 1

all antimicrobial agents that can be used to control microorganisms
can be physical, chemical, mechanical, or biological

Question 2

sterilization

Answer 2

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

Question 3

disinfection

Answer 3

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

Question 4

sanitization

Answer 4

microbial population is reduced to levels that are considered safe by public health standards

Question 5

antisepsis

Answer 5

the destruction or inhibition of microorganisms on living tissue
prevention of infection or sepsis

Question 6

antiseptics

Answer 6

chemical agents applied to tissue to prevent infection by killing or inhibiting pathogen growth

Question 7

chemotherapy

Answer 7

generic term used to describe the application of chemicals to kill or inhibit the growth of microorganisms

Question 8

cidal agents

Answer 8

substances that kill organisms (not necessarily endospores) that have the suffix -cide
ex. bactericide, fungicides, viricides

Question 9

static agents

Answer 9

prevent growth (if chemical is removed, growth will resume)
-static
ex. bacteriostatic, fungistatic

Question 10

D value

Answer 10

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

Question 11

physical means to control microbes

Answer 11

filtration
heat
radiation

Question 12

filtration

Answer 12

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

Question 13

heat

Answer 13

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

Question 14

radiation

Answer 14

• 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

Question 15

phenolics

Answer 15

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

Question 16

alcohols

Answer 16

most widely used disinfectants, antiseptics, and sanitizers
act by denaturing proteins and dissolving membrane lipids

Question 17

halogens

Answer 17

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

Question 18

metals

Answer 18

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

Question 19

quaternary ammonium compounds

Answer 19

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

Question 20

aldehydes

Answer 20

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

Question 21

sterilizing gases

Answer 21

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

Question 22

six factors that affect effectiveness of antimicrobial agents

Answer 22

1. population size
2. population composition
3. concentration or intensity of an antimicrobial agent
4. contact time
5. temp
6. local environment

Question 23

phenol coefficient test

Answer 23

the potency of a disinfectant compared with that of phenol
useful for initial screening but may be misleading

Question 24

dilution test

Answer 24

determines rate at which selected bateria are destroyed by various chemical agents

Question 25

natural control mechanisms of microorganisms

Answer 25

• predation by Bdellovibrio
• bacteriophages
• bacteriocins
• probiotics