Monday, December 2, 2013

Some more questions from student via email

Dear Prof Kwan,

Thanks for your reply. But I have further questions as below. Please kindly
help. Thanks a lot.

1)It is known that the temp of thermophile C. perfringens is 42-47C, but how
about the temp range of mesophile C. botulinum?

A: C. botulinum has optimum temperature of 26-35C.

2)The endospore of C. botulinum is most heat resistant, nearly the last one to
die during cooking, but how come the neurotoxin(heat liable protein)it produced
cannot be eliminated by cooking(as need to be killed by canning which need much
higher temp)?

A: Canning aims to kill the C. botulinum endospores, not the neurotoxins. The neurotoxins are heat sensitive.

3)what organism is mostly grow in red wine based on below condition? (as
yeast/fungi seem cannot grow in high Aw (0.99))

Red wine:
Water Activity     0.99
pH                 4.5
NaCl content w/v           0.5%
Redox (mV)         350
Sugar content      Moderate
Protein content    Low
Keeping temperature 25C

A: Yeasts and fungi can grow at high Aw. Acetic acid bacteria can grow in red wine. But this group of bacteria was not covered in our lectures.

Sunday, December 1, 2013

Note revisions in previous Q & A

Q: Culturing does not detected the pathogen in oysters in winter but the pathogen appears in summer to cause liver infection:_____
Your answer: V. cholerae
I am wondering whether or not V. cholerae could infect liver....

A: I missed the part on liver infection--so it should be hepatitis A

One more question from student via email

Dear Professor Kwan:
Sorry to bother you. I'm really confused about some questions of 5220.
1. causing severe food borne intoxication during famine?
I suggest maybe V. cholera because of famine but V. cholera is not intoxication.
So, I don't know the right answer.

A: not covered in this year's topics. The microbe is Aspergillus flavus, producing aflatoxin.


2. cats as second hosts and infections in immunocompromised people?
Is it Listeria?

A: not covered in this year's topics. A parasite.

3. Bread, 0.85Aw, 6.5pH, 1.0% salt, -50 redox, moderate sugar and protein, 25
temperature, what kind of bacteria exists in it?
Is Hepatitis A virus possible for this one?

A: Viruses can not grow in food. Aspergillus spp.

4. cabbage, 0.99Aw, 5.2pH, 0.5% salt, 350 redox, moderate sugar and low protein,
15 temperature, what kind of bacteria exists in it?

A: Many different bacteria can grow in this food.