BMS2052 Lecture Notes - Lecture 13: Viral Hepatitis, Liver Function Tests, Cell Culture
30 May 2018
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Week 5. Clinical Microbiology and Immunology
CLINICAL MICROBIOLOGY AND IMMUNOLOGY I
• Before lab diagnosis:
o Clinical assessment
o Collection of appropriate specimen (specimen collection)
Swabs: eyes, ear, nose, throat
Fluids: blood (plasma or serum) – most common, urine, sputum (mostly for
respiratory infections)
Tissue: skin, biopsy
Other: stool, pap smear
o Specimen transport
• At the laboratory:
o Specimen reception area:
Cross check details of request and specimen (check DOB/name with doctors etc)
Minimum of three patient identifiers on request card and two on specimen
-especially for names that are common
o Data entry:
Patient details, sample type, test request
Date of collection may also be important
• In the microbiology lab:
1. Microscopy
• Direct examination - Unstained preps
a) Wet mount: usually faecal (eg. see parasites)
b) Indian ink: darkens background not cell (eg. see capsules)
c) Dark field microscopy: eg. syphilis
• Stained preparations:
Gram stain
Acid fast – zhiel-neelson
Fluorescence
• Electron microscopy: now uncommon – can tell you the most likely viruses
• Immunoelectron microscopy (IEM): using specific Ab -> see clumping of virus
particles together – rapid diagnosis
• Advantages:
Rapid – but presumptive diagnosis
Pre-culture information
Easy evaluation for some specimen (urine, faeces)
Provides diagnosis for many fungi, parasites
Bacteria with distinctive morphology or staining characteristics
Virus morphology can be distinctive
Mass screening techniques can be used for diagnosis eg. PCR
• Disadvantages:
Many pathogens are indistinguishable from normal flora
find more resources at oneclass.com
find more resources at oneclass.com
Technical difficulties
Is the agent visualised viable?
Is expensive and uncommon
2. Culture
• Bacteria:
many media types
-special media chromogenic agar is very expensive
different growth conditions
often used in food industry
Pigment production
Presence of haemolysis
Antibiotic susceptibility:
-Disc diffusion method
• Fungi
>50,000 species of fungi but only around 20 are a common cause of
infection
eg. yeast candida sp causes thrush in immunosuppressed women
Most are superficial
Systemic infections
-culture, Ag testing, molecular testing
Fungal culture media:
General purpose: BHI (brain heart infusion from cattle)
Specialist: SDA
Fungal culture:
▪ Dermatophytes and yeast (like little ringworms, superficial)
Meningitis/stroke is common with fungal infections – bird poo is the
main cause
• Viruses
Intracellular organisms
Will not grow on agar/liquid media/matrix
Need living cells for virus culture
Before advent of cell culture systems, viruses were cultivated by
inoculating:
▪ Suitable host animals (influenza was first isolated in ferrets)
▪ Embryonated eggs – influenza virus is stull produced this way
Vaccine production of flu: live virus is injected into fertilised hens egg
-> virus replicates as embryo develops (allantoic fluid) -> virus
containing fluid is harvested from egg (also inactivated)
Culture of animal viruses:
▪ single cell type that can be propagated indefinitely (immortal)
find more resources at oneclass.com
find more resources at oneclass.com
Document Summary
Clinical microbiology and immunology i: before lab diagnosis, clinical assessment, collection of appropriate specimen (specimen collection) Fluids: blood (plasma or serum) most common, urine, sputum (mostly for respiratory infections) Other: stool, pap smear: specimen transport, at the laboratory, specimen reception area: Cross check details of request and specimen (check dob/name with doctors etc) Minimum of three patient identifiers on request card and two on specimen. Especially for names that are common: data entry: Date of collection may also be important. In the microbiology lab: microscopy, direct examination - unstained preps, wet mount: usually faecal (eg. see parasites, indian ink: darkens background not cell (eg. see capsules, dark field microscopy: eg. syphilis, stained preparations: Fluorescence: electron microscopy: now uncommon can tell you the most likely viruses. Immunoelectron microscopy (iem): using specific ab -> see clumping of virus particles together rapid diagnosis: advantages: Easy evaluation for some specimen (urine, faeces) Bacteria with distinctive morphology or staining characteristics.
