Lecture 1: The Role of the Microbiology Laboratory Flashcards
What is a good way to avoid contamination with skin flora, when taking a urine sample?
Taking a sample midstream, as it avoids contamination with anything on skin, and bladder cells or other contaminants with the end stream.
What can prevent the collection of a good urine sample?
If a patient is incontinent, obtaining mid-stream is more difficult. If a patient has a urinary tract infection and cannot urinate as a result, catheter must be used.
What issues can arise from the use of a catheter? (2 Points)
A catheter can move bacteria from lower down the urinary tract to deeper down, potentially compounding the issue.
A catheter is made of plastic, and bacteria stick to plastic very easily forming biofilms.
How can organisms be detected in urine samples? (2 Points)
Microscopy
Solid growth
How is Chocolate Agar made?
After cooling agar to 40dC, then adding horse blood to make blood agar, it is heated again to 80dC, lysing the RBCs and creating an incredibly nutrient rich medium.
What is the purpose of chocolate agar?
To identify fastidious organisms. Such fastidious organisms can include Neisseria meningitidis, Haemophilus influenzae, or Neisseria gonorrhoea.
What is the difference in mechanism between alpha haemolysin and beta haemolysin?
Haemolysin a is a pore forming haemolysin, whereas haemolysin B is a phospholipase C, breaking down phospholipids in the cell membrane, releasing phosphorylcholine.
Does Strep. A have haemolysin a/B?
No, they have their own hemolysins known as streptolysin O and S. (Strep B has only streptolysin S).
What techniques are used in direct microscopy to identify organisms?
Analysing shape and size of organisms, or colony morphology. What variation of haemolysis is present. Stains such as gram stain can be used. Capsular staining is also useful.
What is the role of a microbiology lab in general? (5 Points)
To identify organisms (bacterial, fungal, parasites), thus allowing the prediction of a diseases prognosis, and help with administering treatment.
Can also allow for assessment of antibiotic resistance.
Surveillance of ongoing infection.
Testing of health and safety conditions.
To assist in research concerned with organisms, including antibiotic sensitivities, or to assess significance in general.
What methods are there for detecting and identifying organisms in a blood sample? (8 Points)
Macroscopic features on an agar plate.
Variations of agar, allowing for identification of more fastidious organisms. (chocolate agar and neisseria meningitidis). Temperature and atmosphere changes can also provide clues.
Microscopic features.
Staining. (gram stain, Ziehl-Neelsen, etc.)
Biochemical tests. (oxidase, catalase, coagulase, urease, lancefield grouping)
PCR.
ELISA tests.
MIcroarray tests.
How are antibiotic sensitivities tested?
Inoculated agar plates will have small discs containing known amount of antibiotic placed on them, and rings will form around these discs if organism is susceptible.
What antibiotics are used in most cases of disease?
Various first line antibiotics.
What are some commonly used antibiotics? (7 Points)
- Amoxicillin
- Trimethoprim Sulfamethoxazole
- Erythromycin
- Clarithromycin
- Azithromycin
- Cephalosporin
- Fluoroquinolones
What systemic antibiotics must be monitored closely with serum tests? (2 Points)
Why must these be monitored?
Glycopeptides, such as vancomycin.
Aminoglycosides, such as gentamicin.
Must be monitored because they are only effective above a certain concentration for the entire therapy.
