010 Diagnosis of Bacterial Infection Flashcards
What shape of bacteria is Trepenoma and what disease does it cause? What stain is used?
Syphillus - spiral bacteria - immunofluorescent stain is used (antibody with a fluorescent protein is attached). Acetone breaks the membranes.
Which bacteria are poorly visible on gram stain?
Coxiella, Mycoplasm, Chlamydia, Ricksetta
If a bacteria is gram positive, what color will it stain? What if it is gram negative?
Positive - purple
Negative - pink
What stain is used for Mycobacteria?
Ziehl-Neelson stain
What stain is used for cryptococcus? What type of stain is it?
India ink - negative stain because of the thick capsule
What disease does cryptococcus cause?
Meningitis
What does the silver stain test for?
Pneumocystis jirovec
Describe the structure of Staphylococci
Cocci in clusters
Describe the structure of Streptococci
Cocci in chains
Describe the structure of enterococci
Cocci in pair or short chains
What type of bacteria are vancomycin and erythromycin used to treat?
Gram positive bacteria
What is the major disadvantage of using microscopy of diagnosis?
Very hard to identify the specific bacteria; insensitive; impossible to differentiate between commensal and pathogenic
Other than analysing the bacteria, what other uses can microscopy be used for in diagnosis?
Leucocyte cell counts; if CSF fluid is above 6/mm3 with neutrophils present - it indicates infection. Joints should not have any neutrophils present.
What sort of drugs are used to treat gram negative bacteria?
Aminoglycosides, Tetracyclins
What CSF level is indicative of an infection?
> 6/mm3
What is the major advantage of using culture over EM in diagnosis of bacterial infections?
More sensitive; can be used for further antibody/antigen testing etc.
What are some disadvantages of using cultures in diagnosis?
Takes a long time; hampered by patient antibiotic treatment; some organisms cannot be cultured e
Describe the 3 patterns of haemolysis
alpha - complete (clear inhibition zones)
beta - incomplete (green tinge inhibition zones)
gamma - none (no inhibition)
What are the 2 types of media methods that can be used to identify specific bacteria?
Selective media
Differential media
Give 2 examples of selective media in bacterial diagnosis
- Camphylobactor grows optimally in 42 degrees of stool sample while other organisms do not.
- Specialised antibiotic NYCM is used to focus search for N.gonorrhea in urethra swabs
Give 2 examples of using differential media in bacterial diagnosis
- MacConkey Agar test - contains pH indicator that detects lactose fermentation. Commensal bacteria will ferment lactose (turn it pink) whilst pathogenic bacteria e.g. salmonella will not.
- Tellurite identifies Corynebacteria diptheriae that turns agar black.
How is TB usually diagnosed?
Tuberculin skin test - injecting antigen in a section of the skin. If antibodies are present, then within 2 days there will be a firm red bump. This indicates previous history of TB, but does not indicate whether the TB is active in the minute.
How does urine dipstick testing work? Why might it not be accurate?
Organisms in the urinary tract will produce nitrite from nitrate which can be detected. It might not be accurate if the patient is pregnant, is a child, or has abnormal urinary tract.
How is mycobacterium usually detected?
Through amplification assays (genetic)
How is meningitis usually diagnosed?
Antigen detection methods
What are viridians streptococci?
Streptococci infections that produce alpha haemolysis
