Lecture 8: Lab Features of Microorganisms

Question 1

what are the types of agar plates

Answer 1

• blood
• chocolate
• CLED

Question 2

what shows presence of E. coli

Answer 2

CLED agar produces a yellow colour as teh bacteria ferments lactose to produce acid

Question 3

in which cases is microscopy useful and not useful

Answer 3

useful in sterile sites like cerebrospinal fluid, not useful for non-sterile sites like sputum

Question 4

types of stains

Answer 4

• gram stain for bacteria
• silver stain for fungi like pneumocystis jirovici
• Ziehl Neelsen stain for TB
• Auramine fluorescence for TB

Question 5

ho do we look for viruses

Answer 5

electron microscopy

Question 6

pros and cons of bacterial culture

Answer 6

• slow and labour intensive
• can quantify bacteria
• purification
• antibiotic susceptibility testing

Question 7

how do we identify bacteria from a culture

Answer 7

MALDI-TOF machine which uses mass spectrometry

Question 8

what are the lab techniques to identify difficult to culture organisms

Answer 8

• serology
• molecular techniques eg PCR
• tissue culture

Question 9

what is serology

Answer 9

detection of antibodies

Question 10

what is serology useful for

Answer 10

viral infections and chlamydia and mycoplasma

Question 11

what are limitations of PCR tests

Answer 11

• lab contamination

- latent infections

Question 12

what is PCR useful for

Answer 12

• viral encephalitis (infection of brain tissue)
• mostly caused by enteroviruses, sometimes herpes
• good negative predictive value
• poor positive predictive value
• can be used to detect viral load of HIV, diagnose resistance and early HIV infection

Question 13

what is tissue culture good for

Answer 13

intracellular organisms eg viruses, mycoplasma and chlamydia

Question 14

what are the main ways of doing tissue culture

Answer 14

• seeing cytopathic effects on cells

- detecting viral proteins on surface of cells using immunofluorescence