my notes on Compare and contrast different general approaches for laboratory diagnosis of viral infections.

my notes on Compare and contrast different general approaches for laboratory diagnosis of viral infections.

Microscopy • Time-consuming • Not high throughput • Poor sensitivity • Poor specificity • Subjective • Training • When justifiable? • What samples? • What stains?

Microscopy Unstained preparations: “Wet prep” – Amoeba – Trichomonas vaginalis • Dark-ground illumination for syphilis – Motile spirochaetes
Microscopy Stained preparations- • Gram-stain • Acridine orange • Acid-fast stain – Ziehl-Neelsen • Fluorescence – Direct, e.g. auramine – Immunofluorescence

Factors limiting usefulness of bacteriological investigations • wrong sample – e.g. saliva instead of sputum • delay in transport / inappropriate storage – e.g. CSF • overgrowth by contaminants – e.g. blood cultures • insufficient sample / sampling error – e.g. in mycobacterial disease • patient has received antibiotics

Advantages of Solid Media • isolation of single clonal colonies – get bacterium in pure culture • identify by colonial morphology • quantification by colonyforming units • Organism available for further tests such as susceptibility testing

Disadvantages of Cultivation • Sensitivity – Only 0.1% microbes are cultivable! • Specificity – Overgrowth – Selective medium • Relevance – Multiple isolates • Conditions – Atmosphere – Temperature – Time • Slow • Infection risk

dentification of Bacteria • Morphology • Growth requirements • Biochemistry • Enzymes • Antigens • Molecular typing • Maldi-Tof
Non-cultural diagnostic methods • Antigen detection (Serology) – e.g. latex agglutination, direct immunofluorescence • Antibody detection (Serology) – e. g. agglutination tests, ELISA, indirect immunofluorescence, lateral flow assays, gamma interferon assays • Molecular methods – Polymerase Chain Reaction (PCR) – Hybridisation (microarrays, luminex) – Whole genome sequencing

Susceptibility tests • on solid media – disc diffusion technique • in liquid media – minimum inhibitory concentration (MIC) test • Breakpoint methods • E-test
Antimicrobial agents impregnated into filter paper disc – Control on same plate – Control on different plate • Break points • MIC’s • MBC’s


Susceptibility Testing Problems • Organism in tissues – drug penetration • Microbial biofilms • Mixed cultures • Adverse affect on normal flora • Microbial agent interactions • Selective toxicity • Too slow!

*!!REMEMBER TO STAY POSITIVE LIKE A PROTON!!**