Microbiology Lab Investigations

Question 1

Is it reliable to obtain a specimen from a catheter for urine dipstick?

Answer 1

No, once the urine was in the catheter long enough, the bacteria will be there (almost in every catheter)

* can be done for ketones/glucose but no for infection

Question 2

Is catheter-associated bacteria the same as UTI?

Answer 2

No. Almost all catheter urine specimens will grow bacteria.

• therapy not usually required, unless patient unwell or manipulation, surgery planned

Question 3

What is category 3 laboratory?

Category 4 lab?

Answer 3

High-risk specimens laboratory (safety cabinets etc)

Category 4 lab - infectious diseases w do not have meds to treat for e.g. Ebola

Question 4

What are the benefits of having normal bacterial flora?

Answer 4

• defence against invasive pathogens
• aid in the maturation of the immune system
• assist digestion
• role in toxin degradation

Question 5

What microbe causes tonsillitis with exudates?

Answer 5

Group A Streptococcus

Question 6

Case: young female with pyelonephritis. Her obs look septic.

What investigations would we do?

Answer 6

• blood cultures
• Mid-Stream Specimen of Urine (MSU)
• MRSA screen (all hospital admissions) -> nose and groin swab

Question 7

What’s gram reaction?

Answer 7

Stain used to identify the organisms as gram positive/gram negative

Question 8

Types of gram-positive bacteria

Answer 8

Question 9

Types of gram-negative bacteria

Answer 9

Question 10

What does the lab look for in microscopy inflamed joint? (joint aspirate)

Answer 10

• gram stain bacterie e.g. septic arthritis
• crystals (monosodium urate, calcium pyrophosphate)

Question 11

Examples of microscopy of stool specimens for parasites?

Answer 11

Giardia, Cryptosporidia

Question 12

What special staining technique is used for TB?

Answer 12

Alcohol/acid stain -> e.g. Ziehl-Neelsen or Fluorescent stain (Auramine phenol)

Question 13

What is the specific antigen for C. Diff?

Answer 13

Glutamate dehydrogenase (GDH) in stools

Question 14

What urinary antigens can be found in pneumonia?

Answer 14

• Urinary Legionella antigen
• Urinary Pneumococcal antigen

Question 15

Where can viruses reproduce?

Answer 15

Only in a host cell

Question 16

Examples of viruses that may show latency and persistence

Answer 16

• herpes simplex
• varicella zoster
• HIV

*latency = once we have a primary infection, that virus will stay with us. It will be kept under immune check

Question 17

Example of a virus that will induce lifelong immunity after natural infection

Answer 17

Measles

Question 18

IgM and IgG

What do they tell us?

Answer 18

• IgM - immediate response antibody
• IgG - gradual response antibody (after some time)

Question 19

What do we look at in terms of antibodies in a pregnant woman exposed to Parvovirus?

Answer 19

We look at IgG levels

• if low avidity -> IgG that is recently formed
• high avidity -> IgG that is longstanding

Question 20

What does IgG avidity tells us?

Answer 20

Avidity /pl lapczywosc, chciwosc/ = eagarness, enthusiasm

Avidity testing:

• low avidity -> IgG are only recently formed
• high avidity -> IgGs are longstanding

Question 21

What is PCR commonly used for?

Answer 21

PCR = Polymerase Chain Reaction

• it is used commonly in viral diagnostics (e.g. Influenza, Measles, Herpes encephalitis)

Question 22

Do we need to inform the laboratory when an urgent specimen requires processing?

Answer 22

Yes e.g. in CSF

Question 23

Do we need to inform the laboratory when blood cultures are taken - to process it urgently?

Answer 23

No, because their nature is that they need time to grow within culture medium -> therefore these are started being processed shortly after arrival

* take 8 hours, to ‘next day’