010 Diagnosis of Bacterial Infection

Question 1

What shape of bacteria is Trepenoma and what disease does it cause? What stain is used?

Answer 1

Syphillus - spiral bacteria - immunofluorescent stain is used (antibody with a fluorescent protein is attached). Acetone breaks the membranes.

Question 2

Which bacteria are poorly visible on gram stain?

Answer 2

Coxiella, Mycoplasm, Chlamydia, Ricksetta

Question 3

If a bacteria is gram positive, what color will it stain? What if it is gram negative?

Answer 3

Positive - purple

Negative - pink

Question 4

What stain is used for Mycobacteria?

Answer 4

Ziehl-Neelson stain

Question 5

What stain is used for cryptococcus? What type of stain is it?

Answer 5

India ink - negative stain because of the thick capsule

Question 6

What disease does cryptococcus cause?

Answer 6

Meningitis

Question 7

What does the silver stain test for?

Answer 7

Pneumocystis jirovec

Question 8

Describe the structure of Staphylococci

Answer 8

Cocci in clusters

Question 9

Describe the structure of Streptococci

Answer 9

Cocci in chains

Question 10

Describe the structure of enterococci

Answer 10

Cocci in pair or short chains

Question 11

What type of bacteria are vancomycin and erythromycin used to treat?

Answer 11

Gram positive bacteria

Question 12

What is the major disadvantage of using microscopy of diagnosis?

Answer 12

Very hard to identify the specific bacteria; insensitive; impossible to differentiate between commensal and pathogenic

Question 13

Other than analysing the bacteria, what other uses can microscopy be used for in diagnosis?

Answer 13

Leucocyte cell counts; if CSF fluid is above 6/mm3 with neutrophils present - it indicates infection. Joints should not have any neutrophils present.

Question 14

What sort of drugs are used to treat gram negative bacteria?

Answer 14

Aminoglycosides, Tetracyclins

Question 15

What CSF level is indicative of an infection?

Answer 15

> 6/mm3

Question 16

What is the major advantage of using culture over EM in diagnosis of bacterial infections?

Answer 16

More sensitive; can be used for further antibody/antigen testing etc.

Question 17

What are some disadvantages of using cultures in diagnosis?

Answer 17

Takes a long time; hampered by patient antibiotic treatment; some organisms cannot be cultured e

Question 18

Describe the 3 patterns of haemolysis

Answer 18

alpha - complete (clear inhibition zones)
beta - incomplete (green tinge inhibition zones)
gamma - none (no inhibition)

Question 19

What are the 2 types of media methods that can be used to identify specific bacteria?

Answer 19

Selective media

Differential media

Question 20

Give 2 examples of selective media in bacterial diagnosis

Answer 20

1. Camphylobactor grows optimally in 42 degrees of stool sample while other organisms do not.
2. Specialised antibiotic NYCM is used to focus search for N.gonorrhea in urethra swabs

Question 21

Give 2 examples of using differential media in bacterial diagnosis

Answer 21

1. 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.
2. Tellurite identifies Corynebacteria diptheriae that turns agar black.

Question 22

How is TB usually diagnosed?

Answer 22

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.

Question 23

How does urine dipstick testing work? Why might it not be accurate?

Answer 23

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.

Question 24

How is mycobacterium usually detected?

Answer 24

Through amplification assays (genetic)

Question 25

How is meningitis usually diagnosed?

Answer 25

Antigen detection methods

Question 26

What are viridians streptococci?

Answer 26

Streptococci infections that produce alpha haemolysis