GPB: Bacillus spp.

Question 1

Bacillus spp. basic characteritics

Answer 1

Aerobic, facultative aerobic
Endospore forming
Gram positive bacilli

Question 2

Bacillus groups (2)

Answer 2

B. subtilis
B. cereus - B antracis, B. cereus, B. thuringenesis etc.

Question 3

B. cereus infections

Answer 3

Diarrhoeal disease
Vomiting disease
Localized wound and eye infections
Respiratory and systemic infections.

Question 4

B. cereus diarrhoeal syndrome

Answer 4

Onset 8-16hrs after consumption of contaminated food.
Duration 12-24hrs
Food = meat + vegetable dishes, sauces, pastas, desserts, dairy products.

Question 5

B. cereus emetic disease

Answer 5

Vomiting within 1-5 hours of ingestion of contaminated food
Food - starchy food - rice dishes, milk pudding, pasta, infant formulas.

Question 6

B. cereus non-gastrointestinal disease

Answer 6

Contamination of medical devices
BSI, endocarditis
Meningitis, brain abscesses
Gas gangrene-like cutaneous infections
osteomyelitis
Keratitis

Question 7

B cereus basic characteritics (biochemical tests)

Answer 7

Gram positive bacilli (large box car ends + central spores)
KOH negative
Catalase positive
Oxidase negative

Question 8

B cereus further testing (molecular confirmation)

Answer 8

Vitek
Maldi-tof
PCR - detect ces genes.
Detection of emetic toxins via cell culture assays (Hel 2 cell lines).
Detection of diarrhoeal toxin (Oxoid BCET-RPLA kit / TECRA-BDE kit detection of antibodies produced by Hbl and Nhl respectively)

Question 9

B.cereus treatment

Answer 9

supportive treatment
treat symptoms only

Question 10

Culture conditions

Answer 10

Aerobic 37C blood agar

Question 11

Colonial morphology

Answer 11

large 2-5mm, cream-grey colour (slightly green), dry, irregular edge, B-haemolysis.

Question 12

Gram stain

Answer 12

Gram positive bacilli
Endospores
Large box car ends

Question 14

Presumptive Bacillus spp. tests

Answer 14

1. Sel/Dif agar = PEMBA agar
2. Hanging drop motility test

Question 15

Sel/Dif media test procedure

Answer 15

PEMBA Agar
1. Streak inoculate colony onto agar.
2. Incubate plate at 37C. read at 24 + 48 hrs.

Question 16

Sel/Dif Agar results

Answer 16

B. cereus = large blue crenated colonies with blue egg yolk precipitate surrounding colonies.
B. does not ferment mannitol (blue) and produces lecithinase (hydrolyse lecithin = precipitate appears).

Question 17

PEMBA Agar principle

Answer 17

Contains
Polymixin B = antibiotic that inhibits gram negative bacteria
Egg Yolk = Lecithinase breaks down lecithin in egg yolk forming opaque zone.
Mannitol = fermentation -> yellow colonies
vs no fermentation -> blue colonies.
Bromothymol Blue = pH indicator = if fermentation does not occur there is a alkaline pH and blue colour develops.
If fermentation occurs, pH becomes acidic and colour turns to yellow.

Question 18

Specimens

Answer 18

Clinical = faeces, non-GI tissue, vomitus
Environmental = soil, food.