Microbiology Diagnostics Flashcards
How well does the test detect ALL Individuals positive for a specific organism?
Sensitivity, no false negatives
How well does the test attacked ONLY the individuals positive for a specific microorganism?
Specificity, no false positives
Diagnostic approaches for pathogen identification in a clinical specimen
Microscopy
culture
antigen detection
molecular test (nucleic acid test)
Diagnostic approaches for pathogen identification and culture isolate
Colony morphology
microscopy
antigen test
phenotypic tests (biochemical tests)
molecular tests (proteomics test, nucleic acid test)
Pathogens seen on microcopy
Virus
Bacteria
Fungi
Protozoa
Helmiths
Culture based identification
Identification of bacterial and fungal infections
Bacterial Culture Methods
Agar- colony morphology (size, shape, color, texture)
Blood agar hemolysis
Alpha: partial
Beta: complete
Gamma: none
Phenotypic/biochemical tests are performed on _ culture
Pure
MacConkey Agar
Selective (bile salts inhibit growth of gram +) and differential (lactose present in the media causes organisms to turn pink if they ferment lactose)
grown gram - bacteria
Motility test
Bacteria diffuse through media turning it a hazy color
Catalase test is used to
Differentiate Strep (catalase -) from Staph (catalase +)
Breakdown of H2O2 into O2 and H2O
Oxidase test tests for the presence of
Certain cytochrome C oxidases
+ (associated with color change) result indicates the ability to use oxygen as terminal electron transport acceptor in respiration
Biochemical panels are used for the identification of organisms based on
Phenotypic properties
Molecular tests for pathogen identification
Proteomics (peptide signatures)- species level for bacterial/fungal
Genomic (nucleic acid signatures)- species level identification of bacterial/fungal/viral/parasitic, identification of genes encoding virulence factors and antimicrobial resistance
Proteomics
MALDI-TOF MS
Identifies organisms based on protein spectra
More rapid than traditional biochemical identification
Nucleic acid detection
PCR: target sequence amplified using complimentary primers and probes (multiplex, quantitative)
Isothermal methods
Whole genome sequencing
16S ribosomal RNA gene sequencing
Antigen Detection immunoassays
Lateral flow immunoassays provide rapid antigen detection in clinic settings
Latex agglutination is preformed on culture isolates in lab
Serological diagnosis is based on the presence of
Antibodies and used for viral/bacterial infections
Antimicrobial susceptibility testing (AST)
Genotyping methods used to detect resistance genes
