Which test would I use to identify B. cereus? Enterotube II, Oxi/Ferm Tube II, or API Staph? It's gram positive and oxidase negative. Would any of these tests even work?

A good way to identify Bacillus spp. is by using API 20E, and 50CHB kits. Another way is to insert a special Bacillus card into the VITEK rapid microbial identification machine. Surelly the best way is to use mass spectrometer, but if can't use non of these, you will have to identify the bacterium by biochemical methods.

Here is something that can help you:

Bacillus cereus is:

* Gram positive (but not always. Old bacteria in a culture can be stained Gram-variable)

* Motile

* Beta haemolytic

* Facultatively anaerobic

* Rod diameter under microscope is 1.2μm

* Bacteria tend to form chains

* Hydrolyzes casein, starch and gelatin

* Reduces Nitrate

* Doesn't produce indole

* Doesn't produce gas from Carbohydrates

* Produces acid well from Trehalose

* Grows well on various agars such as: TSBA 5%, CNA, MRSA/MSSA CHROMagar, Chocolate agar.

 

You should also note that despite these biochemical properties sometimes it's quite difficult to distinguish it from other Bacillus speciesת especially: B. amyloliquefaciens and B. thuringiensis.

 

* First picture shows B. cereus colonies swarming over Chocolate agar.

* Second picture shows B. cereus rods forming chains (X1000).

This bacterium was isolated from an ear infection.