Faecal processing

Question 1

What clinical factors/history would suggest that culture for Clostridium difficile should be considered? What kind of specimen?

Answer 1

Hx: hospitalisation and/or having ≥6 wks antibiotic therapy
Specimen: Watery & bloody stools (diarrhoea)

Question 2

What selective and differential media can be used to isolate Clostridium difficile? (write in full)

Answer 2

CCFA (Cycloserine Cefotxitin Fructosa Agar)

Question 3

What clinical factors/history would suggest that culture for Vibrio sp. should be considered? What kind of specimen?

Answer 3

Hx: Overseas travel and/or consumption or seafood (raw/cooked)
Specimen: Watery & bloody stools (diarrhoea)

Question 4

What selective and differential media can be used to isolate Vibrio sp.? (write in full)

Answer 4

TCBS (Thiosulphate Citrate Bile Sucrose agar)

Question 5

List 3-4 viral causes of gastroenteritis?

Answer 5

• Rotavirus
• Norovirus
• Adenoviros
• Astrovirus

Question 6

When referring to GIT infections, what does self limiting mean?

Answer 6

No treatment (antibiotics) except fluid/electrolytes (hydrate)

Question 7

What is the purpose of concentrating faeces?

Answer 7

Increases the chance of seeing parasitic ova, cysts, trophozoites

Question 8

What are the clinical side effects of parasitic infections with Ascaris lumbricoides and Hookworms?

Answer 8

Ascaris lumbricoides: Abdominal discomfort/cramping, nausea, vomiting, diarrhoea
Hookworms: Itchy, localised rash, Abdominal pain, diarrhoea, anaemia, loss of appetite

Question 9

How could you differentiate a Campylobacter species from a Pseudomonas species on CAMP agar? At least two features. (see non-fermenter and GIT lectures)

Answer 9

GRAM: Camp. = GN helical/curved
Pseud. = regular GNB
COLONY MORPH: Camp. tear-drop colonies along streaked lined
Pseud. = flat, irregular, metallic sheen colonies

Question 10

What features would lead you to suspect that a Salmonella sp. was growing on an XLD plate and in a TSI slope + urea slope? How would you confirm this? What about Shigella? (see GIT lecture)

Answer 10

XLD: Red colony w/ black center (Salmonella sp), Red colony (Shigella sp)
TSI: Red slope & black butt (Salmonella), Red slope yellow butt (Shigella)
Urea: Neg (Salmonella & Shigella)
Confirm w/ Antisera (Poly O & Poly H =Salmonella. Poly O= Shigella)

Question 11

What colour reactions would Salmonella Typhi and S. Paratyphi A, B, C produce in TSI tubes? (see GIT lecture)

Answer 11

Salmonella Typhi= weakly H2S pos (some black in TSI)
S. Paratyphi B, C= H2S pos (Black at butt/base)
S. Paratyphi A= H2S neg (no black)

Question 12

When testing organisms isolated from faeces, what does a positive urea tube indicate?

Answer 12

Normal flora (Proteus, Providencia, Morganella)

Question 13

Under what circumstances might antibiotic therapy be prescribed for a GIT infection?

Answer 13

• Severe infection or chronic infection in babies

- Elderly & immunocompromised

Question 14

If a TSI slope was red (slope), black (middle) and yellow (butt) and the organism tested negative for Salmonella using serological reagents, what other organism could be indicated? How would you ID/confirm this?

Answer 14

Edwardsiella sp. (similar TSI result as Salmonella)

=> confirm ID w/ API20E+ or MALDITOF

Question 15

Define Dysentry symptoms

Answer 15

blood, mucous, pus in stools (caused by inflammation on intestinal wall)

Question 16

Difference between cysts/oocytes and Eggs/ova

Answer 16

cysts/oocytes from protozoa

Eggs/ova from worms

Question 17

Indication of seeing charcot-leyden crystals in wet mount

Answer 17

charcot-leyden crystals = breakdown of WBC products = parasitic infection