LAB 1 - – INTRODUCTION TO CLINICAL MICROBIOLOGYy Flashcards
What are the 4 risk groups? Explain them.
- Normal flora; will not cause disease in a healthy person but opportunistic in immunocompromised hosts (Lactobacilli)
- Cause disease that are treatable with antibiotics (S. aureus)
- High risk to individuals; low-risk to community (B. anthracis)
- High risk to individual and community; cause serious disease that is highly transmissible (Ebola virus)
What is the difference between chemical disinfection and sterilization?
- In what situations would you use each?
Chemical disinfection: kills specific pathogens using chemical means
- used for surfaces/ inanimate objects that cannot be autoclaved
Sterilization: complete elimination of all live microorganisms
What conditions are necessary for the autoclave?
Time: 15 minutes
Temperature: 121°C
Pressure: 106 kilopascals
Which organism is used to prove sterility after autoclaving ?
Geobacillus stearothermophilus
Explain the principle of gram staining.
1. How would your stain be affected if your smear was too thick?
- based on peptidoglycan differences of gram+ve and gram-ve bacteria
- crystal violet dye diffuses into organism and is trapped by iodine in peptidoglycan layer(s)
- decolorizing agent (acetone) dehydrates thick gram+ve cell walls; dye in inner walls cannot pass through = remains purple
- thinner gram-ve cell walls are decolorized and crystal violet is washed away
- safranin counterstains gram-ve cell walls that have not trapped crystal violet = pink
. What are common causes of over-decolorization? Try to name at least 4.
- Non-intact cell walls due to excess heat fixation
- Excess time
- Insufficient crystal violet/ iodine
- Excessive washing b/w steps
- Excessive counterstain
Explain the principles of the following Brightfield microscopy and Koehler illumination
- Light source is below the specimen
- Objects are visualized bc stains absorb light differentially or bc objects are thick enough despite being colorless
- Koehler is a technique that improves focus and image illumination of transmitted and reflected light
Explain the principle of Darkfield microscopy
- Examines delicate living organisms (ie. spirochetes) that are difficult to stain
- Oblique light is illuminated by a special condenser
- Deflected light (from bacteria) are displayed as illuminated bodies against a black background
Phase contrast microscopy
- Can examine living transparent organisms without staining
- Reveals differences in cells and their structure not discernible by brightfield or darkfield microscopy (flagellar movement of Trichomas vaginalis)
Explain the principle of Fluorescence microscopy
- Organism stained with dyes/ fluorochromes absorbs energy from UV light and re-emits it at a longer wavelength
- Includes a high intensity light source, exciter filter, and suppression filter
