Lab Diagnosis Flashcards
direct specimen
no normal flora present; collected from normally sterile tissue and body fluids (lung, liver, blood, CSF)
indirect specimen
no normal flora present at site BUT specimen passes through a site with normal flora during collection, becoming contaminated (vomit, urine, sputum)
specimen from site with normal flora
pathogen and normal flora are mixed at infection site (throat swab, stool, etc.); selective media for culture of pathogen or discounting normal flora
specimen transport
buffered liquid or semi-solid media with minimal nutrients, prevent drying, maintain neutral pH, minimize contaminant growth
anaerobic cultures
specimens with normally sterile sites (wound, CSF, joint fluid; NO sputum, urine, stool)
anaerobic culture transport
tissue in dry container with no oxygen, liquid in container with special medium
light microscopy used for _
gram stain, acid-fast stain, decolorize, counterstain
fluorescence microscopy used for _
auramine-rhodamine stain, mycobacteria in sputum (TB)
gram stain
differentiate gram positive and negative
acid fast stain
used when gram stain doesn’t work due to mycolic acid; confirms auramine-rhodamine test for mycobacteria
pink/red acid-fast
acid-fast positive (mycobacteria)
blue acid-fast
acid-fast negative (not mycobacteria)
nucleic acid amplification tests (NAAT)
PCR, transcription-mediated amplification
when are NAATs done?
before culture, directly on specimen
PCR used for _
c. diff, mycobacterium tuberculosis, bordetella pertussis, chlamydophila pneumoniae, mycoplasma pneumoniae
c. diff PCR
specimen is diarrhea sample
m. tuberculosis PCR
specimen is sputum sample
pertussis, atypical pneumonia PCRs
specimen is nasal swab
transcription mediated amplification (TMA)
based on repeated amplification of ribosomal RNA of microorganism
TMA used for _
neisseria gonorrheae or chlamydia trachomatis (genital swab or urine)
When is TMA done?
directly on specimen, before culture
immunological methods
antigen detection and detection of Ab against pathogen (serology)
antigen detection mechanisms
enzyme immunoassay, latex agglutination
enzyme immunoassays used for _
group A strep (throat swab), E.coli (stool), legionella pneumophila (urine)
latex agglutination
antibody on beads
latex agglutination used for _
staph. aureus AFTER culturing from specimen
serology done at LSUHS
t. pallidum (syphilis)
bacterial cultures
agar plates, blood culture bottles, MGIT tubes
EMB agar
only gram-negative will grow
blood agar
many things grow
chocolate agar
many things grow, including haemophilus (flu)
hektoen enteric agar
salmonella and shigella (e. coli)
example of bacteria on EMB agar
k. pneumoniae
example of bacteria on chocolate agar
streptococcus pneumoniae, s. aureus, k. pneumoniae, h. influenzae
example of bacteria on blood agar
streptococcus pneumoniae, s. aureus, k. pneumoniae
hemolysis
some bacteria secrete toxins that can lyse RBCs which can be detected on a blood agar plate
complete hemolysis
beta
partial hemolysis
alpha
no hemolysis
gamma
hektoen enteric agar for stool
salmonella or shigella
MacConkey/sorbitol agar for stool
distinguishes e. coli’s
campy agar for stool
campylobacter
MacConkey agar mechanism
based on ability to ferment lactose –> bacteria that can will turn agar pink, such as e. coli
usual contaminant in blood cultures
staph. epidermidis (USE ANTISEPTIC WIPES!!)
which will almost always represent a true infection when found in blood culture?
s. aureus, e. coli, streptococcus pneumoniae, pseudomonas aeruginosa
mycobacteria growth indicator tube (MGIT)
several specimen types (sputum, pleural fluid), treated with chemicals to inactivate normal flora; growth detected by UV light
tests for identification of organisms after culture
manual (spot) tests or automated systems
spot tests
catalase, coagulase, oxidase
catalase spot tests
all staphylococci will be positive and all streptococci will be negative
coagulase spot tests
s. aureus is positive and s. epidermidis is negative
oxidase spot tests
neisseria and pseudomonas are positive
automated systems at LSUHS
mass spec, microscan
mass spectrometry
ID takes two minutes; ID by analysis of ribosomal proteins-high abundance
does mass spec give any info on antibiotic susceptibility?
no
microscan system
multiwell plates each having a different ingredient (carbohydrate, protein, or nitrogen compound) and will test which ones the bacterium can metabolize
Which plates will test for antibiotic sensitivity in the microscan system?
gram(-) and gram(+); NOT yeast
