Lab 7 Infections of Enteric and Hepatobiliary system Flashcards
(41 cards)
4-year-old boy, sudden onset of lower abdominal pain and diarrhea of frequent small stools with tenesmus. The patient was febrile with mild tenderness over the left lower abdomen, blood and mucus was noticed in his stool. A stool specimen was collected for microbiological investivation.
What are teh common diarrgea pathogens? 4 examples.
- Shigella
- Salmonella
- Campylobacter
- Vibrio
4-year-old boy, sudden onset of lower abdominal pain, and diarrhea of frequent small stools with tenesmus. The patient was febrile with mild tenderness over the left lower abdomen, blood and mucus were noticed in his stool. A stool specimen was collected for microbiological investigation.
Why are selective and/or differential culture media being used to culture stool samples? Which type of culture media is not recommended?
To identify diarrheal pathogens from normal flora.
Non-selective medium such as blood agar
The MacConkey agar and the Deoxycholate agar (DCA) both became yellow with colonies formed. What does it suggest?
Became yellow = non-lactose fermenter (= there are diarrheal pathogens rather than only normal flora)
Potentially a Shigella/ Salmonella
In the disc diffusion sensitivity test, there are clear zones around antibiotic discs of Chloramphenicol, Ciprofloxacin, and also Cefotaxime. What does it mean?
For this 4-year-old patient, which drug would you use? Why?
It means that the bacteria are susceptible to these antibiotics because the antibiotics can suppress its growth.
Chloramphenicol should not be used due to severe bone marrow suppression. (existed as topical and IV form)
Ciprofloxacin is not used due to cartilage malformation in animals, C/I in children, only use as a last resort.
Therefore, Cefotaxime is preferred.
What is DCA (Deoxycholate citrate agar) for?
To determine lactose fermenter (red) vs non-lactose fermenter (yellow) and H2S producers (black)
Slide agglutination test (SAT) is a serological method to? How does it work?
To identify the organism - Salmonella/ Shigella in which its sera contains specific antibodies to Salmonella/Shigella in stool.
List all the Enterobacteriaceae which are non-lactose fermenters. (4)
How can they be further differentiated by their ability to produce H2S ?
- Shigella
- Salmonella
- Proteus
- Yersina
Non-motile and non-H2S producers:
- Shigella
- Yersinia
Motile and H2S producers:
- Salmonella
- Proteus (swarming motility)
For lactose fermenter, the color of MacConkey agar and DCA agar?
MacConkey agar: red
DCA agar: remains pink
non-lactose fermenter: becomes yellow
List 4 species of Shigella.
- Shigella dysenteriae
- Shigella boydii
- Shigella flexneri
- Shigella sonnei
(dysenteriae, boy, flex, sony)
How to differentiate Shigella from Salmonella by DCA?
Salmonella is H2S producing therefore shows black in DCA agar while Shigella does not.
Pathophysiology of Shigella? (2)
Direct invasion of mucosal cells, but does not invade further.
By Shiga toxin (Enterotoxins)
> ShET1, ShET2
Clinical presentations of Shigella infection? (3)
Bacillary dysentery - Diarrhea - from watery to bloody - high fever - HUS (hemolytic uremic syndrome) (human is the only reservoir)
Clinical presentations of Salmonella infection? (group + name of species) (6)
- Osteomyelitis in sickle cell disease patients
- GE group: S. enteritidis (chicken); S. choleraesuis
- Typhoid fever group: S. typhi, S. paratyphi
Is Salmonella or Shigella infection a notifiable disease?
Only Shigella is
Both Salmonella and Shigella is transmitted via Faecal-oral route. Which is acid-stable and which is acid labile?
Shigella is acid-stable (with low infective dose needed)
Salmonella is acid-labile (thus increase the risk of infection in patients with reduced acid production in the stomach, e.g. pernicious anemia )
Which of the following about Escherichia coli is incorrect?
A. Not all E.coli causes diarrhea
B. 90% of the UTI cases are due to E.coli
C. It is the 1st MC cause of neonatal meningitis
D. EHEC O157:H7 can cause HUS
E. EHEC O104:H4 causes HUS in 2011, an outbreak in Germany
C: should be 2nd MC cause;
1st most common cause is GBS (Group B Streptococcus)
What are the common features under a microscope between Vibrio and Campylobacter?
Both of them are curved rods G- bacilli.
List 4 characteristic features of the Genus Campylobacter.
- Seagull shape
- Best grown at 42 degrees (thermophilic)
- requires less O2 (microaerophilic)
- Shows silver tear-drop colonies on Skirrow agar
Which of the following about Vibrio is incorrect?
A. It is comma-shaped
B. It is oxidase +
C. It is a glucose fermenter
D. It grows on alkaline peptone medium (+)
E. It is a sucrose fermenter
E: not necessary!!
TCBS for differentiating sucrose fermenter or not!
Sucrose fermenter = yellow =
Vibrio cholerae
green = -ve, V.parahaemolyticus
Campylobacter is spread via ________ reservoir.
poultry
Name the 3 species of Vibrio and their clinical manifestations. (6)
- Vibrio cholerae: cholera
- Vibrio parahaemolyticus: GE
- Vibrio vulnificus: necrotizing fasciitis
Other than self-limiting bloody diarrhea, what are the 2 other clinical manifestations of infections by Campylobacter?
- Reactive arthritis
2. Post-infection (more prone to?): Guillain Barre Syndrome
60/F sudden onset of diarrhea consisting of yellowish loose stool for 1 day. She was dehydrated and ran a low grade fever. She had consumed left over roasted goose.
On Deoxycholate citrate agar, showed black centered colonies which turned yellow.
What does it indicate? (2)
Probable diagnosis? (1)
Black - H2S positive (either salmonella or proteus, but proteus does not cause diarrhea)
Yellow agar - non-lactose fermenter
Salmonella gastroenteritis!!!!
(NOT SALMONELLA)
What is the management plan for Salmonella gastroenteritis? (2)
Self-limiting.
Non pharmacological: Fluid electrolyte replacement= rehydration
Pharmacological: Abx e.g. quinolones if indicated (systemic involvement)
*but abx is C/I, because it may causes further spread of the Samonella in the body by killing in and releasin more contents
