Microbio Lab 8 Flashcards
antimicrobials
any compounds that kill or inhibit microorganisms
antibiotics
antimicrobials, usually of low molecular weight, naturally produced by microorganisms to inhibit or kill other microorganisms
ex. penicillin and streptomycin
semi-synthetics
antimicrobials that are chemically synthesized in the laboratory and are not produced by microbial biosynthesis at all
ex. sulfa drugs
healthcare acquired infections (HAIs)
formerly nosocomial infections; acquired in hospitals; MRSA is responsible for many hospital infections
Kirby-Bauer method
used to determine the sensitivity or resistance of a bacterium to an antimicrobial
performed by streaking a standardized inoculum of the test organism on Mueller-Hinton medium, and then paper disks containing specific concentrations of an antimicrobial are deposited on the agar surface. The antimicrobial diffuses out from the disk into the agar, forming a concentration gradient. If the agent inhibits or kills the test organism, there will be a zone around the disk where no growth occurs, called the zone of inhibition.
Mueller-Hinton II agar is the recommended medium with pH between 7.2 and 7.4
zone of inhibition
the zone around the disk where no growth occurs if an agents inhibits the microorganism; affected by diffusibility of the agent, size of the inoculum, the type of medium, and other factors
antiseptics
substances such as alcohol or betadine that inhibit microbial growth or kill microorganisms but they are gentle enough to be applied to living tissue; do not destroy endospores
disinfectants
chemical agents that are applied to inanimate objects such as floors, walls, and tabletops to kill microorganisms; damaging to living tissue
sterilants; sporocides
destroy all microbial life, including endospores
ex. ethylene oxide
sanitizers
agents that reduce microbial numbers to a safe level but do not completely eliminate all microbes
bacteriostatic
if a particular agent only inhibits the growth of bacterial cells but does not kill them
bacteriocidal
agents that kill bacterial cells
Heat affects…
proteins (enzymes)
nucleic acids (DNA and RNA structure)
other small molecules
thermal death point
the lowest temperature at which a population of the target organism is killed in 10 minutes
thermal death time
the shortest time required to kill a suspension of cells or spores under defined conditions at a given temperature
UV radiation at 260 nm
the most germicidal because it the wavelength at which DNA maximally absorbs UV light
pyrimidine dimers
covalent bond between two adjacent thymine or cytosine molecules in a DNA strand; caused by absorption of UV light
SOS system
enzymatically removes the dimers and inserts in their place new pyrimidine molecules.
Ultraviolet (UV) Light
Nonionizing short-wavelength radiation that falls between 4nm and 400nm in the visible spectrum; more germicidal than either visible light or infrared radiation
Why are endospores resistant to to UV light?
1) the DNA of endospores is protected by small acid-soluble proteins that bind to DNA and alter its conformation, thereby protecting it from photochemical damage
2) a unique spore photo-product is generated by UV light in endospores that functions in the enzymatic repair of damaged DNA during endospore germination
Antibiotic resistant strains
Staphylococcus aureus Pseudomonas aeruginosa Mycobacterium tuberculosis Neisseria gonorrhoeae Enterococcus
They are a problem in HAIs and is a major health problem
Narrow-spectrum antimicrobials
Specific in target
Ex. Targets gram-positive or gram-negative
Broad-spectrum antimicrobials
Effective against both gram- positive and negative organisms
Types of modes of action for antimicrobials
Target cell wall synthesis (penicillin)
Target DNA and RNA synthesis (cipro, rifampin)
Target protein synthesis (tetracyclines, streptomycin)
Target vitamin synthesis (sulfa drugs)
Affects whether an antimicrobial is narrow or broad
Permeability also affects function (harder to penetrate gram-negative cells)