micro poop 4. Flashcards
What are the five general approaches used to detect the cause of infections?
microscopy, culture, detection of antigens, demonstration of nucleic acids (molecular techniques), detection of antibodies (serology)
What is the problem with using conventional clinical microbio culture?
4 days minimum to review culture results - longer for other organisms
When is the best time to collect specimen?
acute phase of infection
gram stain
differentiates bacteria based on staining characteristics of bacterial cell wall - also demonstrates cellular material and inflammatory response
gram positive - clusters = ?
staph
gram positive - chains = ?
strep
Culture
traditional method of determining causative agent - microorganisms have specific nutritional and growth requirements
how long does culture take?
commonly encountered - 48-72 hours plus 24 hours for antimicrobial testing
What are advantages/disadvantages of antigen detection?
advantages: more rapid, inexpensive disadvantages: poor sensitivity and limited availability
What are antigen detection tests being replaced with?
molecular assays (hybridization and nucleic acid amplification assays) due to increased sensitivity and specificity
What are advantages/disadvantages of serology?
advantages: serum easy to obtain, tests widely available, ease of transport disadvantages: IgG tests require acute AND convalescent sera, IgM can have false+/-, 2-3 week delay with short incubation periods
IgM in serum
appears in serum in 1-2 weeks, persists for 2-3 months, consistent with current or recent infection
IgG in serum
appears 2-3 weeks after infection, may persist for life, somewhat recent infection or immunity, or past infection
Antibody titers in serum
higher dilution is consistent with higher level of antibody in serum (1:2, 1:4, 1:8) - 4 fold rise in titer is diagnostically significant
What are problems with cell culture?
long period required for result, poor sensitivity, contamination risk, toxic substances may be present, many do not grow in culture
