micro - microbial diagnoses

Question 1

Lab Tests and Procedures for diagnosing microbial infections

Answer 1

Direct microscopic examination of clinical specimens, ex. Sputum, CSF, etc.

Gram and acid-fast stain

India ink (CSF for Cryptococcus neoformans)
KOH treatment for fungal forms
Fluorescent antibodies

Question 2

More procedures for diagnosing microbial infec.

Answer 2

Growing bacteria, fungi and viruses
Use of enriched and selective media (bacteria & fungus) or appropriate cell types (viruses) for cultivation of clinical specimens

Question 3

More procedures for diagnosing microbial infec.

Answer 3

3) Tests for enzymes and metabolic pathways
Catalase, oxidase, lactose fermentation, etc.

4) Specific antiserum detection of microbial antigens
Quelling reaction
Slide agglutination
Virus neutralization

5) Identification of serum antibodies
No antibody early in infection (appear ~ 2wks after infection)
Does not differentiate between past and present infection (only way to tell is IgM is the first antibody to appear - if its is there and present, then it must be present)
Need accurate and convalescent sample to confirm active infection
Tests include:
Complement fixation
Hemagglutination and hemagglutination inhibition
Latex agglutination
Enzyme-linked immunosorbent assays (ELISA)
Western blots

• *6. Detection of microbial proteins and nucleic acids**
• Western blots and ELISAs - microbial proteins
• Southern blots - microbial DNA
• Northern blots – microbial RNA

Question 4

ELISSA TEST

look for any antigen in the serum - indicates infection.

2nd antibody is then bound…enzyme label makes a specific color

(E stands for enzyme…this test used a lot in clinical micro)

Answer 4

7. Detection of microbial genes
Known gene probes which are single-stranded and labeled are hybridized with clinical samples
Frequently need a polymerase chain reaction (PCR) to amplify DNA sequences in clinical specimens ex. Nested PCR