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BS2002 Microbiology > W9 Control of Microorganisms > Flashcards

W9 Control of Microorganisms Flashcards

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Biology 101 flashcards
1
Q

definition of antisepsis

A

chemicals applied to body surfaces to destroy or inhibit pathogens

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2
Q

definition of sanitation

A

reduction of microbial population to levels deemed safe

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3
Q

disinfection

A

destruction or removal of pathogens, but not bacterial endospores

usually used on inanimate objects

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4
Q

definition of sterilisation

A

the complete removal or destruction of all viable microorganisms

used on inanimate objects

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5
Q

definition of chemotherapy

A

chemical used to kill or inhibit growth of microorganisms within host tissues

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6
Q

definition of log kill

A

quantitative measurement to indicate effectiveness of a treatment in reducing number microorganisms

1 log kill: reduction of 90%

2 log kill: reduction of 99%

3 log kill: reduction of 99.9%

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7
Q

the pattern of microbial death

A

microorganisms are not killed instantly

population decline occurs exponentially

killing efficiency is measured using decimal reduction time which is the time to kill 90% of population

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8
Q

conditions influencing effectiveness of antimicrobial agent activity

A

population size

population composition: sensitivity differs markedly to antimicrobials

concentration of microbial

duration of exposure to treatment

temperature

local environment (eg H or viscosity)

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9
Q

what is moist heat treatment

A

efficient way of killing microorganisms including viruses. fungi, protists and bacteria

water penetrates into organic carbon bonds > degrades nucleic acids, denatures proteins and disrupts membranes through hydrolysis

spores are more heat and moisture resistant than vegetative cells

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10
Q

conditions for autoclaving (steam sterilisation)

A

carried out using autoclave

performed above 100 degrees which requires saturated steam under pressure

saturation requires good penetration so everything must be open

effective against all types of microorganisms including spores

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11
Q

what is pasterurisation

A

controlled heating to reduce bacteria number

process does not necessarily sterilise (kill 100%) but does kill pathogens present and slow spoilage by reducing the total load of organisms present

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12
Q

what is dry heat sterilisation

A

using high temperature (hot air) to kill microorganisms

less effective than moist heat sterilisation

requires higher temperatures and longer exposure times

usually not applicable to food as it oxidises cell constituents and denatures proteins

useful for solids that are affected by moist heat but unchanged by high temperature

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13
Q

how does ionising radiation work

A

using gamma radiation to penetrate deep into objects

destroys bacterial endospores; not always effective against viruses

non radioactive

used for sterilisation and pasteurisation of antibiotics, hormones, sutures and food etc

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14
Q

how is uv radiation used as treatment

A

wavelength of 260nm as it is where most bacterial dna absorbs

causes thymine dimers > prevent replication and transcription

limitation: UV does not penetrate glass, dirt films, water > limited to surface decontamination

used for water treatment

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15
Q

properties of using phenolics as chemical agent

A

used as labs and hospital disinfectants

tuberculocidal > effective in presence of organic material and long lasting

act by denaturing proteins and disrupting cell membranes

disagreeable door and can cause skin irritations

tricolsan used in hand sanitisers

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16
Q

properties of alcohols used as chemical agents

A

bactericidal, fungicidal but not sporicidal

inactivate some viruses

denature proteins and possibly dissolve membrane lipids

most effective when used at 70% with water

17
Q

properties of using iodine as chemical agent

A

skin antiseptic

used a lot in surgery prep

oxidises cell constituents and iodinates proteins

at high concentrations may kill spores

skin damage, staining and allergies can be a problem

18
Q

properties of using chlorine as chemical agent

A

oxidises cell constituents

destroys vegetative bacteria and fungi

chlorine gas is sporicidal

can react with organic matter to form carcinogenic compounds

19
Q

properties of using heavy metals as chemical agents

A

combine with and inactivate proteins, may also precipitate proteins

effective but usually toxic

20
Q

properties of using quaternary ammonium compounds as chemical agents

A

amphipathic organic cleansing agents

safe and say to used but inactivated by hard water and soap

target integrity of the cell envelope

kill most bacteria but not endospores

21
Q

properties of using aldehydes as chemical agents

A

highly reactive molecules > toxic

combine with and inactivate nucleic acid and proteins

sporicidal and can be used as chemical sterilant

22
Q

properties of using sterilising gases as chemical agents

A

used to sterilise heat sensitive materials

microbidical and sporicidal

eg: ehtylene oxide sterilisation is carried out in autoclave

eg: vaporised hydrogen peroxide combine with and inactivate dna and proteins

23
Q

what are virion-associated peptidoglycan hydrolases and endolysin

A

vision-associated peptidoglycan hydrolase: used by bacteriophage to make a hole in bacteria to allow dna injection (initial infection)

endolysin: used by bacteriophages to lyse the peptidoglycan at the end of the cycle to release the virus

24
Q

differences between bactericidal and bacteriostatic agents

A

bactericidal: kill bacteria > kills pathogens and many non pathogens but not necessarily endospores

bacteriostatic: only inhibits bacteria growth, not killing it

25
Q

general characteristics of antimicrobial drugs

A

ability to kill or inhibit pathogen while damaging host as little as possible

either narrow or broad spectrum drugs: attack few or many different pathogens respectively

side effects

toxic dose

therapeutic index: ratio of toxic dose to therapeutic dose

26
Q

how is effectiveness of antimicrobial drugs measured

A

minimal inhibitory concentration (MIC): the lowest concentration of drug that inhibits growth of pathogen

minimal bactericidal/lethal concentration (MBC/MLC): lowest concentration of drug that kills pathogen

27
Q

what does the ability of the drug to reach site of infection depend on

A

the mode of administration: oral, topical or parenteral routes

28
Q

how does disk diffusion test (Kirby Bauer method) work

A

disks impregnated with specific drugs placed on agar plates inoculated with test microbe

drug diffuses from disk into agar > establish concentration gradient

larger zones > bacteria more susceptible to antibiotic

smaller or clear zones > bacteria is resistant

29
Q

what is the E test

A

used to determine MIC (similar to disk diffusion method but uses strip rather than disk)

bacterial suspension spread on agar > plastic strip with gradient of antibiotic placed on agar with markings indicating antibiotic concentration

antibiotic diffuses onto agar > create gradient of concentration in medium > point where ellipse intersects the strip corresponds to MIC > the lowest concentration that inhibits bacterial growth

30
Q

mechanisms of antibiotics

A

inhibitors of cell wall synthesis

protein synthesis inhibitors

nucleic acid synthesis inhibition

metabolic antagonists

31
Q

how do some bacteria become resistant to penicilin

A

penicilin contains b lactam ring which is essential for bioactivity

penicilin resistant organisms produce beta lactamase > hydrolyse a bond in the ring > break down the ring > become ineffective

32
Q

mode of action of penicilins

A

blocks enzyme DD-transpeptidases that catalyses transpeptidation (formation of cross links in peptidoglycan)

prevents synthesis of complete cell walls > lysis of cell

acts only on growing bacteria that are synthesising new peptidoglycan (will not work on bacteria that already have cell wall)

33
Q

how do some antibiotics inhibit protein synthesis

A

many bind specifically to the bacterial ribosome

binding can be to small or large ribosomal subunit

others inhibit a step in protein synthesis such as: aminoacyl-tRNA binding, peptide bond formation, mRNA reading or translocation

34
Q

what are amino glycoside antibiotics

A

contain a cyclohexane ring and amino sugars

bind to 30s ribosomal subunit and interfere with protein synthesis by directly inhibiting the process and causing misreading of mRNA

resistance and toxicity

35
Q

mechanisms of drug resistance

A

modification of target enzyme (spontaneous mutation)

inactivation of the antibiotic

antibiotic altering enzymes

drug efflux (pump drug out of the cell)

use of alternative pathways/enzymes

36
Q

origins of transmission of drug resistance

A

immunity genes: antibiotic-producing microbes have resistance genes that protect them from their own antibiotics

horizontal gene transfer: transfer of immunity genes from antibiotic producers to non-producing microbes

37
Q

where can resistance genes be found on

A

bacterial chromosomes

plasmids

transpoons

phages

can be freely exchanged between bacteria when found on mobile genetic elements

BS2002 Microbiology (11 decks)

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