Micro Unknown Quick Question

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Hi everyone!

Doing my Identity of the Unknown report, and it all adds up to be Bacillus Cereus except that my Urea test was negative. My notes indicate that b. cereus should test positive for urea. I'm just wondering if my notes are wrong.

Does anyone know if b cereus should be positive or negative for urea? I'm not finding much info online.

Thanks so much!

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Specializes in ICU.
Hi everyone!

Doing my Identity of the Unknown report, and it all adds up to be Bacillus Cereus except that my Urea test was negative. My notes indicate that b. cereus should test positive for urea. I'm just wondering if my notes are wrong.

Does anyone know if b cereus should be positive or negative for urea? I'm not finding much info online.

Thanks so much!

Hmmmm....Googling urease test with B. cereus gives different results. Apparently, some strains are urease +, while others are urease -. See:

Role of ureolytic activity in Bacillus cereus nitr... [Appl Environ Microbiol. 2008] - PubMed result

(out of 49 strains tested, 10 were urease +) This suggests that the bug is generally (your mileage may vary) urease negative.

Another web page says that the bug is urease negative:

Biochemical Properties of Bacterial Contaminants Isolated from Livestock Vaccines

"...Bacillus cereus ...were positive to catalase and oxidase, while negative to urease and methyl red."

On a FAR more important note (to me, at least), B. cereus is the bug responsible for fried rice syndrome. Even after you boil/steam rice, B. cereus spores can survive, then germinate at room temp as the rice sits out on your kitchen counter. As they grow, they make some nice heat stable toxins.

See:

Elsevier

Bacillus cereus - Wikipedia, the free encyclopedia

Cooking temperatures less than or equal to 100 °C (212 °F) allows some B. cereus spores to survive.[7] This problem is compounded when food is then improperly refrigerated, allowing the endospores to germinate.[8]... enterotoxins, one of which is highly resistant to heat and to pH between 2 and 11;[10] ingestion leads to two types of illness, diarrheal and emetic (vomiting) syndrome.[11] Bacterial growth results in production of

  • The diarrheal type is associated with a wide-range of foods, has an 8- to 16.5-hour incubation time and is associated with diarrhea and gastrointestinal pain. Also known as the long-incubation form of B. cereus food poisoning, it might be difficult to differentiate from poisoning caused by Clostridium perfringens.[10]
  • The emetic form is commonly caused by rice that is not cooked for a time and temperature sufficient to kill any spores present, then improperly refrigerated. It can produce a toxin, cereulide, which is not inactivated by later reheating. This form leads to nausea and vomiting 1-5 hours after consumption. It can be difficult to distinguish from other short-term bacterial foodborne pathogens such as Staphylococcus aureus.[10]

So which is better - diarrhea or emesis? Fun, fun, fun!

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Hmmmm....Googling urease test with B. cereus gives different results. Apparently, some strains are urease +, while others are urease -. See:

Role of ureolytic activity in Bacillus cereus nitr... [Appl Environ Microbiol. 2008] - PubMed result

(out of 49 strains tested, 10 were urease +) This suggests that the bug is generally (your mileage may vary) urease negative.

Another web page says that the bug is urease negative:

Biochemical Properties of Bacterial Contaminants Isolated from Livestock Vaccines

"...Bacillus cereus ...were positive to catalase and oxidase, while negative to urease and methyl red."

On a FAR more important note (to me, at least), B. cereus is the bug responsible for fried rice syndrome. Even after you boil/steam rice, B. cereus spores can survive, then germinate at room temp as the rice sits out on your kitchen counter. As they grow, they make some nice heat stable toxins.

See:

Elsevier

Bacillus cereus - Wikipedia, the free encyclopedia

Cooking temperatures less than or equal to 100 °C (212 °F) allows some B. cereus spores to survive.[7] This problem is compounded when food is then improperly refrigerated, allowing the endospores to germinate.[8]... enterotoxins, one of which is highly resistant to heat and to pH between 2 and 11;[10] ingestion leads to two types of illness, diarrheal and emetic (vomiting) syndrome.[11] Bacterial growth results in production of

  • The diarrheal type is associated with a wide-range of foods, has an 8- to 16.5-hour incubation time and is associated with diarrhea and gastrointestinal pain. Also known as the long-incubation form of B. cereus food poisoning, it might be difficult to differentiate from poisoning caused by Clostridium perfringens.[10]
  • The emetic form is commonly caused by rice that is not cooked for a time and temperature sufficient to kill any spores present, then improperly refrigerated. It can produce a toxin, cereulide, which is not inactivated by later reheating. This form leads to nausea and vomiting 1-5 hours after consumption. It can be difficult to distinguish from other short-term bacterial foodborne pathogens such as Staphylococcus aureus.[10]

So which is better - diarrhea or emesis? Fun, fun, fun!

Cruffler!!! Thanks SO MUCH for such an in depth response! I never imagined anyone would take that much time!

I found a couple other websites that seem to support Urease negative results for b. cereus. So, what do you think? Should I cross my professor in my report and suggest that his notes are wrong? :)

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Specializes in ICU.
cruffler!!! thanks so much for such an in depth response! i never imagined anyone would take that much time!

i found a couple other websites that seem to support urease negative results for b. cereus. so, what do you think? should i cross my professor in my report and suggest that his notes are wrong? :)

you're quite welcome!

suggest that your prof is wrong, you ask??!!?? do you like to live dangerously?

a far better approach might be to contact your prof (in person, via email, or voicemail), asking for clarification on the expected urease results for b. cereus. of course your prof's notes couldn't be incorrect. it's just that you, as an incompetent (:D) student, might have accidentally misunderstood the most holy documents transmitted to you from your prof.

that way, you're not directly challenging the prof, you're not directly asking for the "correct" answer, yet you'll hopefully be seen as a dedicated student searching for "truth."

it's not about right or wrong - it's all about how you play the game.

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Specializes in ICU / PCU / Telemetry / Oncology.

Did you consider re-doing the urease test to see if you get the same result? Perhaps there is a chance you contaminated something the first time? I think this is the best way to confirm that what you did was proper.

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Specializes in Cardiac.

Very few in my class got perfect results for our unknowns. Some tests are more reliable than others so if you weigh your results appropriately then you should be able to identify your bug.

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Did you consider re-doing the urease test to see if you get the same result? Perhaps there is a chance you contaminated something the first time? I think this is the best way to confirm that what you did was proper.

Good idea, Paco. Unfortunately, that test in particular was done for me and given to me to read on the day of the unknown experiments.

I ended up quoting some of the places that indicated a negative urease test was a possibility, and I also suggested that perhaps the urease test was performed too early - that by the time i was able to read the results, the positive test had faded to appear negative.

Otherwise, it all lines up to be Bascillus cereus. We'll see. Thanks so much, everyone, for all your help!

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