W9 Control of Microorganisms Flashcards
definition of antisepsis
chemicals applied to body surfaces to destroy or inhibit pathogens
definition of sanitation
reduction of microbial population to levels deemed safe
disinfection
destruction or removal of pathogens, but not bacterial endospores
usually used on inanimate objects
definition of sterilisation
the complete removal or destruction of all viable microorganisms
used on inanimate objects
definition of chemotherapy
chemical used to kill or inhibit growth of microorganisms within host tissues
definition of log kill
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%
the pattern of microbial death
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
conditions influencing effectiveness of antimicrobial agent activity
population size
population composition: sensitivity differs markedly to antimicrobials
concentration of microbial
duration of exposure to treatment
temperature
local environment (eg H or viscosity)
what is moist heat treatment
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
conditions for autoclaving (steam sterilisation)
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
what is pasterurisation
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
what is dry heat sterilisation
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
how does ionising radiation work
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
how is uv radiation used as treatment
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
properties of using phenolics as chemical agent
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
properties of alcohols used as chemical agents
bactericidal, fungicidal but not sporicidal
inactivate some viruses
denature proteins and possibly dissolve membrane lipids
most effective when used at 70% with water
properties of using iodine as chemical agent
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
properties of using chlorine as chemical agent
oxidises cell constituents
destroys vegetative bacteria and fungi
chlorine gas is sporicidal
can react with organic matter to form carcinogenic compounds
properties of using heavy metals as chemical agents
combine with and inactivate proteins, may also precipitate proteins
effective but usually toxic
properties of using quaternary ammonium compounds as chemical agents
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
properties of using aldehydes as chemical agents
highly reactive molecules > toxic
combine with and inactivate nucleic acid and proteins
sporicidal and can be used as chemical sterilant
properties of using sterilising gases as chemical agents
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
what are virion-associated peptidoglycan hydrolases and endolysin
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
differences between bactericidal and bacteriostatic agents
bactericidal: kill bacteria > kills pathogens and many non pathogens but not necessarily endospores
bacteriostatic: only inhibits bacteria growth, not killing it
general characteristics of antimicrobial drugs
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
how is effectiveness of antimicrobial drugs measured
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
what does the ability of the drug to reach site of infection depend on
the mode of administration: oral, topical or parenteral routes
how does disk diffusion test (Kirby Bauer method) work
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
what is the E test
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
mechanisms of antibiotics
inhibitors of cell wall synthesis
protein synthesis inhibitors
nucleic acid synthesis inhibition
metabolic antagonists
how do some bacteria become resistant to penicilin
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
mode of action of penicilins
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)
how do some antibiotics inhibit protein synthesis
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
what are amino glycoside antibiotics
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
mechanisms of drug resistance
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
origins of transmission of drug resistance
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
where can resistance genes be found on
bacterial chromosomes
plasmids
transpoons
phages
can be freely exchanged between bacteria when found on mobile genetic elements
