Clinical Microbiology Flashcards
ILOs
Understand classical approaches employed in the clinical microbiology laboratory
Be aware of current advancements in approaches to clinical microbiology
Leading types of HCAIs
- UTIs - 34%
- Surgical site infections - 22%
Why study cause of infection?
Prognosis
Treatment
Isolation
Care
How is the cause of an infection determined? Patient Specimin
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Rapid tests and immunoassays
- Bacteria and fungi: biochemical identification
- Bacteria, fungi, protozoa and viruses: ELISA, flow cytometry, complement fixation
2. Microscopy
- Light: bacteria, fungi, protozoa
- Electron: viruses
3. Culture - Bacteria and fungi: purify and amplify
- Viruses: cytopathology
4. Biochemical Tests
- Bacteria and fungi: identification and sensitivity
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Molecular Testing
- Bacteria, fungi, protozoa, viruses: nucleic acid amplification, sequencing, fingerprinting
How is the cause of an infection determined? 1. Historical workflow
Historical workflow:
- stain-based methodologies for classification of microscopic morphology to support early diagnostic and therapeutic decisions
- microbial culture for propagation of the offending organism on agar or in liquid medium
- biochemical or antigenic techniques for the subsequent metabolic and phenotypic analysis of the microorganism, ultimately leading to microbe identification
- antimicrobial susceptibility testing to confirm therapeutic choices or tailor therapy
How is the cause of an infection determined? 2. Stains for microscopy - Gram Stain
The Gram stain
– Classic stain for differentiating between Gram –ve and Gram +ve bacteria
![](https://s3.amazonaws.com/brainscape-prod/system/cm/256/101/229/a_image_thumb.png?1539465056)
How is the cause of an infection determined? Stains for microscopy - Acid Fast Stain
![](https://s3.amazonaws.com/brainscape-prod/system/cm/256/101/438/q_image_thumb.png?1539465129)
• Acid fast stain for tuberculosis
– Also known as the Ziehl- Neelson stain
• Advantages – Specific
– No need for culture
– Performed directly on sputum
How is the cause of an infection determined? Stains for microscopy - PAS (periodic acid-Schiff)
![](https://s3.amazonaws.com/brainscape-prod/system/cm/256/101/560/q_image_thumb.png?1539465216)
• PAS (periodic acid-Schiff)
– Stains for glycoproteins, often used for fungi
• Disadvantages
– High background
How is the cause of an infection determined? Microbial culture
Selective media
– E.g. Mannitol salt agar, used for the isolation of Staphylococci.
Differential media
– MacConkey agar, recovery of Enterobacteriaceae.
![](https://s3.amazonaws.com/brainscape-prod/system/cm/256/101/648/a_image_thumb.png?1539465279)
How is the cause of an infection determined? Biochemical techniques - G+
![](https://s3.amazonaws.com/brainscape-prod/system/cm/256/101/719/q_image_thumb.png?1539465392)
![](https://s3.amazonaws.com/brainscape-prod/system/cm/256/101/719/a_image_thumb.png?1539465470)
How is the cause of an infection determined? Biochemical Techniques - G-
![](https://s3.amazonaws.com/brainscape-prod/system/cm/256/101/901/a_image_thumb.png?1539465515)
How is the cause of an infection determined? Biochemical techniques: API strips
![](https://s3.amazonaws.com/brainscape-prod/system/cm/256/101/925/q_image_thumb.png?1539465604)
• Typically carried out using API strips (Analytical profile index)
– 20 biochemical tests simultaneously
![](https://s3.amazonaws.com/brainscape-prod/system/cm/256/101/925/a_image_thumb.png?1539465613)
How is the cause of an infection determined? Agglutination assays
![](https://s3.amazonaws.com/brainscape-prod/system/cm/256/102/025/q_image_thumb.png?1539465665)
- Doesn’t require culture
- Used frequently for detection of viral infections
- Conversely lack of agglutination in some assays is the measure of infection
- visualise as a change in turbidity of solution
![](https://s3.amazonaws.com/brainscape-prod/system/cm/256/102/025/a_image_thumb.png?1539465732)
How is the cause of an infection determined?
![](https://s3.amazonaws.com/brainscape-prod/system/cm/256/102/064/q_image_thumb.png?1539465809)
ELISA – Enzyme Linked ImmunoSorbent Assay
Direct and indirect ELISA
Capture ELISA
![](https://s3.amazonaws.com/brainscape-prod/system/cm/256/102/064/a_image_thumb.png?1539465977)
Direct ELISA
![](https://s3.amazonaws.com/brainscape-prod/system/cm/256/102/188/a_image_thumb.png?1539465885)