Lab1 Questions Flashcards
Advantage of using solid medium to grow bacteria?
Bacteria separated on surface form isolated colonies
each colony = progeny of 1 bacterium
facilitates isolation of bacteria
Why isolate pure cultures of bacteria?
to determine properties (structure, phys, biochem, pathog)
not possible to study in mixed culture
why gram stain of your urine specimen fail to reveal bacteria when inoculum grew many colonies?
urine sample = too few bacteria/volume
usually centrifuge urine to concentrate bacteria
define differential media
uses particular bacterial biochem property to differentiate one organism from another
define selective media
allow growth of organisms you want but suppresses growth of other organisms
how is macconkey both selective and differential
selective by adding bile salts and crystal violet
to see gram-negative enteric and inhibit gram positive enteric
differential using ability to ferment lactose
lactose fermenter = pink+red
NOT fermenter = colorless
explain how initial gram stain of abd abscess aspirate helps you clinically
gram rxn and morphology on stain helps choose initial empiric antimicrobial
what would you do if initial gram stain for abscess negative?
if no bacterial on gram stain, could be
1) low # of organisms in culture (considered sterile until compare with results of culture)
2) treat pt empirically
3) modify when culture available
gram stain shows gram-positive cocci and gram-negative rods
cultures grew streptococci
why did gram negative bacteria not grow in culture?
gram-negative rods = anaerobes
even though anaerobic cultures performed, swab was not a good collective vehicle for abscess material as organisms couldn’t grow since briefly exposed to oxygen
what principles to stain flagella?
flagella stain = mordant that precipitates on flagella to increase their size
what principle to stain capsule
use negative stains (India ink); capsule = clear zone btwn bacteria and background
use positive stains that interact with capsule (CuSO4)
what principle to stain endospore
more resistant than vegetative bacteria
in gram stain endospore = unstained region in stained cell
positive stains = entry of stain, decolorize to remove stain from vegetative bacteria
17 y/o female with mild back pain
urine sample taken
culture grew 100,000 colonies/mL of E coli
how likely she has UTI
Unlikely
urine is good growth medium and pt’s urine had several hours to grow before processing
likely specimen contained few than 100,000 organisms @ collection
