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Dr.Habiib:
Aden is a businessman 55-year old who just coming from Germany experience attacks of bloody diarrhea and abdominal cramps. He states that he had a hamburger sandwich with green salad. Culture of stools on MocConkey`s medium reveals pure culture of rose pink colonies. Examination of Gram-stained film from colonies shows Gram-negative bacilli.

1. What is the possible causative organism of this condition?

2. What is serotype that we know to cause like these symptoms before 2011?

3. What is the medical importance of this organism?

4. What is the virulence factor of this organism?

5. How can you a definite diagnosis be reached?

6. What is the most common nosocomial infection of this organism? Explain the mode of this infection.

7.  In generally what is the epidemiologic investigation we make it if out breaks of infection occur?



   By  Dr.Habiib

Dr.Adnan:
1- E. coli O104:H4
2- E. coli O157:H7
3- Have been associated with much chance of developing HUS (Hemolytic Uremic syndrome)
4-shiga toxin
5-Bacterial culture  is the most definitive but time consuming so PCR can be used (not sure if developed for this strain yet)
6-I would generalized and say it causes UTI, Mode of transmission is feco-oral .
7-usually we investigate vegetable markets and meat products.

Dr.Habiib:



Thank you Dr.Adnan  , well done

This one of latest cases in this year 2011 after outbreak of E.coli occur in Germany, so you must make every time updating your knowledge because medicine is not a fixed.

Answers:
1. Causative organism is: E.Coli type O104:H4

2. Serotype before 2011 causing these symptoms is: E. Coli    O157:H7


3. E.Coli has the fallowing medical importance:
 a - It is the most predominant facultative anaerobes in large intestine of man.
b- It is a part of normal bowel flora.
c- Although there are certain pathogenic strains which, under special circumstances, are responsible for serious intestinal and extra intestinal diseases, E.Coli as normal flora provides protection against colonization by harmful microorganism.
d- E.coli is used as one of important of faecal pollutions of water since it is constantly found in human and animal faeces.


4. This new strain the virulence factor is: shiga toxin


5. The definite diagnosis we can reach: Full laboratory Diagnosis

a- Specimen: faeces

b- Gram-stain: tells only that is gram negative bacilli

c- Cultivation:  stool should be plated on MocConkey`s agar as well as blood agar.

d. Identification:

1- After 24h incubation, colonies should be examined for morphology, Gram-stain and oxidase.
2- Colony showing Gram-negative bacilli and oxidase negative is considered as an Enterobacteriaceae organism.
3. E. coli usually produce rose pink colonies on MocConkey`s medium.

4. Colonies should be tested biochemically:
- Fermenters to glucose, lactose, maltose, mannite, sucrose and salicin with production of acid and gas.
- Indole-positive, methyl red, Voges-Proskauer(VP) negative and Citrate-negative.

   After that you should be further tested serologically and for virulence factor to confirm its enteric pathogenicity.

- Slide agglutination using specific antisera.
- Tissue culture methods for toxin production.
- ELISA can be used also to test for toxin production.
- DNA probe or PCR to detect genes of toxin production.



6. The most nosocomial infection of E.coli is urinary tract infection.
 - mode of infection: I mean here how to make UTI, we can say as following:
Organism from faecal flora usually enter the urinary tract by ascending from the perineum and peri-urethral sites( ascending infection).



7. The epidemiologic investigation we make it if out breaks of infection occur is bacterial typing:
Typing of individual strains of an organism is major factor in epidemiological investigations, such as tracing the source of infection in outbreak infections.
The bacterial strains isolated from clinical specimens obtained from the patient should be same type as that isolated from suspected source(s).
Different typing methods are available for different organism. Examples include:
- Typing by colony morphology.
- Bacteriophage-typing.
- Biotyping.
- Serotyping.
- Plasmid analysis.
- Ribotyping.
- Chromosomal analysis and others.

 

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