Apr26 M3-Diagnostic Microbiology Laboratory Flashcards
diff bacteria dx methods
- microscopy
- culture
- bacterial ID (biochem tests, ID systems)
- susceptibility testing
- serology
- nucleic acid-based detection (PCR)
steps of gram stain
- heat-firxed smear with specimen stained with crystal violet (purple)
- add iodine fixor (KI)
- alcohol to decolorize
- counterstain with safranin
gram positive cocci in clusters is what organism
staph aureus
gram negative rods: think of what organism
e.coli
gram negative diplococci think of what organism
neisseria meningitidis
acid-fast stain is used for what
mycobacteria spp (includes TB)
acid-fast stain is based on what (what will you stain)
will stain the many LIPIDS on the mycobacteria CELL WALL
acid-fast stain steps
- stain with carbolfuschin (red) + heat (stain mycobacteria red if have any)
- acid alcohol to decolorize
- counterstain with methylene blue (stain background blue for contrast)
partially acid fast organisms
- Nocardia spp (gram+ rod)
- Actinomyces spp (gram+ rod)
- *gram + rods**
how do you do your acid fast stain with partially acid fast organisms
use lower concentration of acid alcohol to decolorize
appearance of mycobacteria spp on acid fast stain (Ziehl-Neelsen)
red rods
5 types of culture media
- general purpose
- enriched
- selective
- differential
- specialized
goal of general purpose culture + agar used
- detect most aerobic and facultatively anaerobic organisms
- sheep’s blood agar
enriched culture: goal + agar used
- grow organisms like Haemophilus influenza that don’t grow on sheep blood
- added nutrients for fastidious organisms
- chocolate agar
selective culture: goal + agar used
- bring out specific bacteria (and suppress others)
- MacConkey agar if want to bring out gram+ and suppress gram-
differential culture: goal + agar used
- group microbes based on characteristics seen on medium (diff based on hemolysis and who ferments lactose)
- sheep blood agar, MacConkey agar
specialized culture: goal + agar used
-additives (Abs to suppress specific pathogens and growth factors to select others) to isolate specific pathogen
alpha hemolysis charact + organisms
- partial hemolysis of RBCs, greenish hue
- strep pneumoniae and strep viridans
beta hemolysis charact + organisms
- hemolysin produced breaks down RBCs
- beta hemolytic strep (Group A,B,C,G strep) and staph aureus
gamma hemolysis charact and organisms
- no hemolysis
- enterococcus
purple vs no colour meaning on MacConkey plate
- purple = lactose fermenters (pH stain and reaction with purple crystal violet in the medium
- no color = not lactose fermenter
typical lactose fermenter
E.coli
next step after plating specimens on selected agars
must incubate them
4 environments of incubation for culture and what organisms prefer these
- aerobic
- microaerophilic (less O2) = campylobacter
- CO2 rich = streptococcus
- anaerobic environment (C.diff, dies in presence of O2)
what do you get when ask for blood culture
two bottles
- one for aerobic org test
- one for anaerobic
what does a blood culture bottle contain
- liquid nutritionally enriched media
- device or resin for antibiotic removal
- anticoagulant
what is done with blood cultures after collection
incubated at 35C for 5 days in continuous monitoring system
2 ways the continuous monitoring system senses culture growth in a bottle
- pH sensitive membrane in bottom of bottle, senses change bc of CO2 released from metabolism
- can detect color change
(3. can also use sensors)