What are the principles of how organisms can be detected in clinical specimens?
microscopy, culture, molecular
Name common stains used for microscopy
- Gram stains
- Acid fast stains: Ziehl Neelsen, Auramine Fluorescent, Immunofluorescence/Labelled antibodies
What type of organisms that can be detected using common stains used for microscopy?
- Mycobacteria primarily
- Immunofluorescence/Labelled antibodies:Detect antigen in clinical material, Can be operator dependent e.g. Legionella, Chlamydia, some viruses, Pneumocystis
How are cultures used to detect microorganisms?
- Grow organisms to detect and identify them
- pure culture needed for ID and susceptibility testing
What are the types of cultures used to detect microorganisms?
- Agar
- Broth
What is agar?
Solid, like a firm jelly Derived from red algae Can see colonies Easier to work with many different types of agar Selective and differential
What is broth?
- Liquid medium
- More sensitive: i.e. able to detect smaller numbers of organisms
- Need to subculture onto solid media prior to identification
What is molecular detection?
- Look for presence of organism’s nucleic acid: DNA/RNA
- Very sensitive – can detect small numbers of organisms
What are the methods of molecular detection?
- Polymerase chain reaction (PCR) or similar
- Multiple nucleic acid amplification techniques are available
Name some of the common clinical samples that can be submitted to the microbiology lab
- urine
- pus and swabs
- swabs
- tissue
- sputum
- stool
Name samples that have normal flora
- Sputum
- Vaginal swabs
- Superficial swabs
- Urine (if poorly collected) and/or stool
Name samples that do not have normal flora
- Blood
- CSF
- Pleural, pericardial, peritoneal
- Tissue (deep)
What is the difference between samples that have/do not have normal flora?
- Samples containing normal flora are non-sterile
- Sample that do not contain normal flora are obtained from sterile sites and are more helpful
