Question from a student 20170429b

Q:

I am trying 2014-15 past paper and have the following question on B4(e): I would like to know what is expected for "justify and explain" after calculating the required values. 

A: 

“justify and explain” means you need to justify the bases for your making the conclusion--which should be based on deduction and elimination. Also you need to explain how the conclusion was derived. In this case, you calculate and get some numbers. You need to explain how you use the numbers to come to the conclusion.

Question from a student 20170429

Q:

From: LLLLL

Dear Prof. Kwan,

Will ALL the topics of the 3 sets of microbiology notes be covered? Are there any exceptions?

Best regards, 

A:

Only the topics covered in the lectures will be included in the examination. Of course, the materials in the sets of notes under the topics will be included too.

Food Alert - (*Updated on 28 April 2017) A kind of prepackaged smoked salmon which might be contaminated with Listeria monocytogenes 食物警報 - (2017年4月28日更新資料) 一款可能受李斯特菌污染的預先包裝煙三文魚

Dear Sir/Madam,

We have issued a food alert regarding "(*Updated on 28 April 2017) A kind of prepackaged smoked salmon which might be contaminated with Listeria monocytogenes".

Please check the following link for further details.
http://www.cfs.gov.hk/cgi-bin/cfsnew/fa/foodalert_e.pl?record=176

For further enquiries, you may contact us at <rc@fehd.gov.hk>.
Should you wish to cancel your registration with E-news, please notify us either by email (same address as above) or by fax (no. 2893 3547).

Centre for Food Safety

***********************************************************

各位先生/女士：

我們剛發出關於"(2017年4月28日更新資料) 一款可能受李斯特菌污染的預先包裝煙三文魚"的食物警報。

詳情請參閱以下連結:
http://www.cfs.gov.hk/cgi-bin/cfsnew/fa/foodalert_c.pl?record=176

如有任何查詢，請與我們聯絡(電郵地址：rc@fehd.gov.hk)。
如想取消[食物安全電子信息]的用戶登記，請透過上述電郵地址或傳真號碼 2893 3547 通知我們。

食物安全中心


 

Food Alert - A batch of prepackaged smoked salmon contaminated with Listeria monocytogenes 食物警報 - 一批受李斯特菌污染的預先包裝煙三文魚

Dear Sir/Madam,

We have issued a food alert regarding "A batch of prepackaged smoked salmon contaminated with Listeria monocytogenes".

Please check the following link for further details.
http://www.cfs.gov.hk/cgi-bin/cfsnew/fa/foodalert_e.pl?record=176

For further enquiries, you may contact us at <rc@fehd.gov.hk>.
Should you wish to cancel your registration with E-news, please notify us either by email (same address as above) or by fax (no. 2893 3547).

Centre for Food Safety

***********************************************************

各位先生/女士：

我們剛發出關於"一批受李斯特菌污染的預先包裝煙三文魚"的食物警報。

詳情請參閱以下連結:
http://www.cfs.gov.hk/cgi-bin/cfsnew/fa/foodalert_c.pl?record=176

如有任何查詢，請與我們聯絡(電郵地址：rc@fehd.gov.hk)。
如想取消[食物安全電子信息]的用戶登記，請透過上述電郵地址或傳真號碼 2893 3547 通知我們。

食物安全中心


 

Questions from a student 20170425

From LLLLL,

I have come across the following problems during my revision. I hope you don’t mind that the questions may be a bit long. Thank you very much.

1.               From the notes I jotted during lesson, I have written down Clostridium perfringens can survive in oxygen but can’t grow in it, while Clostridium botulinum can’t survive in oxygen. I am wondering if I have jotted notes wrongly as they are both obligate anaerobes. So what is ‘obligate anaerobe’ actually?

A. "obligate anaerobic": organism that can only grow or survive in anaerobic conditions and not in aerobic conditions. Those die in aerobic condition can definitely NOT able to grow in aerobic condition.

2.               Regarding 2012-2013 past paper, I have checked the answers in the blog that ‘Aspergillus oryzae’ may most preferentially grow in bagel with redox potential -50mV. However, on notes p.95 about characteristics of molds, molds are obligate aerobes and they require high redox for growth. I don’t quite understand why molds can grow in the bagel with such low redox-potential. Does it mean that the bagel actually rely on the oxygen in the atmosphere to grow, but not rely on the bagel?

A. Molds are not all obligate aerobes. They can ferment and grow on sugar. P.95 refers to spoilage fungi that are obligate aerobes growing on organic acids. It is unclear and needs to be updated.

3.               Regarding naked virus and enveloped virus, naked virus has a cell wall while enveloped virus does not? Cell wall=protein coat? If yes, enveloped virus also has a protein coat… If not, then what is the main structural difference between them except the envelope membrane?

A. Naked virus has protein coat, not cell wall. Enveloped virus has both membrane and protein coat. Membrane is the main structural difference between them.

4.               According to the factsheet of WHO dated 2002, Salmonella was considered as one of the emerging foodborne pathogens. Is it not applicable nowadays?

A. In some cases such as relating to produce, Salmonella is emerging. Emerging is not a tight definition.

5.               Some questions about endospore-forming bacteria

è Take the preparation of fried rice as an example (Bacillus cereus):

a) rice cooking activates endospore germination (if cooking temperature is high enough, endospores can possibly be eliminated? Since I remember in the case of roasting turkey, you have mentioned that the cooking temperature may not be high enough to kill the endospores. That means cooking at improper temperature will activate spore germination, while at the same time can’t kill the endospores?) A. Yes

b) cooked rice that is held under room temperature favours growth A. Should be Germination of endospores and secret toxins

c) cooked rice is then fried at temperature that is not high enough to kill the endospores thus become problematic (or should it be temperature is not high enough to destroy the toxins?)  A.  Toxin is a problem and also vegetative cells after germination.

Do the events above correctly describe the situation?

6.               Will the final examination cover the content below?

-               Soybean paste

-               Clostridium difficile

A. No.

Sorry for asking so many questions. Thank you very much for your attention.

Question from a student 20170426

Q:  I would like to ask whether we could bring the printed powerpoints for the final exam (besides the 3 sets microbiology notes)?

A:  

All paper materials can be used in the open-book examination.

Review session 2

More notes on examination

I wish you acquire and use these skills and capabilities:

1. logical
2. attention to details
3. organized
4. thorough
5. careful in calculation
6. familiarize--internalize knowledge
7. read questions carefully
8. good time mangement

Question from a student 20170423a

Question

From: GGGGGG
Sent: Sunday, April 23, 2017 5:23 PM
To: hoishankwan@cuhk.edu.hk
Subject: Question

Can you help me check my answer? 

2014-2015 past paper question B4 (e)

(e)

(i) 

Spores D = 12 

New D value = 2.5/10 = 0.25 

0.25 x 12 = 3 min 

Bacteria D = 13 

New D value = 0.25/15 = 0.0167 

0.0167 x 13 = 0.2171

(ii)

Bacteria 100 ml --> 100D reduction = 10 ^(-98) /ml 

Spores 10/ml --> 10D reduction = 10 ^(-9) / ml 

Bacteria: D = 10

0.0167 x 10 = 0.167 min

Spores : D = 9 

0.25 x 9 = 2.25 min 

Thanks 

Answer: To be answered in review session 2 on 24/4/2017

Discussion: 

Question from a student 20170423

TO BE ANSWERED IN REVIEW SESSION 2 ON 24/4/2017 MONDAY

From CCCCC, a question on the exercise..........................

The student requested email answer and not on the blog. So I deleted her email here and I will work the question in the review session with you students and then I will send my answer via email to the student.

The exercise is as follows:

	a.	45 of the patients joined a company picnic together with another 115 employees.  Lunch was served during the picnic: Menu—Pizza (with toping of  ham, olive, pineapples, and green pepper), shrimp salad, roasted turkey, and bread.
	b.	Lunch in the picnic was served at 12:00 noon on Saturday.
	c.	45 patients started to have diarrhea at  2:00pm on Saturday followed by severe vomitting.  They went to the hospital immediately.  The last patient went to the hospital at 4:00pm on Saturday.
	d.	The hospital laboratory detected low levels of Salmonella enterica subspecies typhimurium (serotype O14) from the feces of 15 patients.
	e.	The laboratory of the Health Department detected low levels of Salmonella enterica subspecies typhimurium (serotype O14) and low levels of Staphylococcus aurues from the shrimp salad that was left over from the food served during the picnic and then refrigerated after lunch.  Low  levels of Clostridium perfringens  spores were found in the vegetable stock, part of  which was used to make the turkey stuffing.  No bacteria or spores were found from bread or pizza.
	f.	The laboratory traced the sources of the food.  Some dough was collected from the pizza house which supplied the pizzas for the picnic.  No bacteria were found in the dough.
	g.	The turkey and bread was prepared in the morning and transported to the picnic area without refrigeration.  The shrimp salad was also made in the morning, stored in a foam box with some ice and transported to the picnic area.  The pizzas were baked right before lunch time and transported to the picnic area while they were kept at 65-70°C.
	h.	Most of the patients recovered after one day of rest.

        

i.	The foods consumed at breakfast and lunch and the illness records are listed in the following table, calculate the attack rates.  Which food would be the suspected food?  Explain briefly.                                                                                                       (4 marks)

Foods served	Ate				Did not Eat
	Well	Ill	Total	Attack rate	Well	Ill	Total	Attack rate
Pizza	78	10	88		37	35	72
Shrimp salad	56	33	89		51	10	61
Roast turkey	78	25	103		30	20	50
Bread	96	40	136		19	5	24

ii.	Using the information provided,  suggest a hypothesis to describe the outbreak.  Describe the implicated microorganism(s) involved, their transmission, food implicated, and events that caused the outbreak.  Explain your answer.                                 (12 marks)

iii.	How could the outbreak be prevented?                                                                  (4 marks)