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MICBI - Clinical MICBI > Lab 7 Infections of Enteric and Hepatobiliary system > Flashcards

Lab 7 Infections of Enteric and Hepatobiliary system Flashcards

1
Q

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.

A
  1. Shigella
  2. Salmonella
  3. Campylobacter
  4. Vibrio
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2
Q

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?

A

To identify diarrheal pathogens from normal flora.

Non-selective medium such as blood agar

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3
Q

The MacConkey agar and the Deoxycholate agar (DCA) both became yellow with colonies formed. What does it suggest?

A

Became yellow = non-lactose fermenter (= there are diarrheal pathogens rather than only normal flora)

Potentially a Shigella/ Salmonella

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4
Q

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?

A

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.

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5
Q

What is DCA (Deoxycholate citrate agar) for?

A

To determine lactose fermenter (red) vs non-lactose fermenter (yellow) and H2S producers (black)

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6
Q

Slide agglutination test (SAT) is a serological method to? How does it work?

A

To identify the organism - Salmonella/ Shigella in which its sera contains specific antibodies to Salmonella/Shigella in stool.

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7
Q

List all the Enterobacteriaceae which are non-lactose fermenters. (4)
How can they be further differentiated by their ability to produce H2S ?

A
  1. Shigella
  2. Salmonella
  3. Proteus
  4. Yersina

Non-motile and non-H2S producers:

  1. Shigella
  2. Yersinia

Motile and H2S producers:

  1. Salmonella
  2. Proteus (swarming motility)
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8
Q

For lactose fermenter, the color of MacConkey agar and DCA agar?

A

MacConkey agar: red
DCA agar: remains pink

non-lactose fermenter: becomes yellow

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9
Q

List 4 species of Shigella.

A
  1. Shigella dysenteriae
  2. Shigella boydii
  3. Shigella flexneri
  4. Shigella sonnei

(dysenteriae, boy, flex, sony)

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10
Q

How to differentiate Shigella from Salmonella by DCA?

A

Salmonella is H2S producing therefore shows black in DCA agar while Shigella does not.

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11
Q

Pathophysiology of Shigella? (2)

A

Direct invasion of mucosal cells, but does not invade further.

By Shiga toxin (Enterotoxins)
> ShET1, ShET2

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12
Q

Clinical presentations of Shigella infection? (3)

A 
Bacillary dysentery - Diarrhea
- from watery to bloody
- high fever
- HUS (hemolytic uremic syndrome)
(human is the only reservoir)
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13
Q

Clinical presentations of Salmonella infection? (group + name of species) (6)

A
  1. Osteomyelitis in sickle cell disease patients
  2. GE group: S. enteritidis (chicken); S. choleraesuis
  3. Typhoid fever group: S. typhi, S. paratyphi
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14
Q

Is Salmonella or Shigella infection a notifiable disease?

A

Only Shigella is

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15
Q

Both Salmonella and Shigella is transmitted via Faecal-oral route. Which is acid-stable and which is acid labile?

A

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 )

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16
Q

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

A

C: should be 2nd MC cause;

1st most common cause is GBS (Group B Streptococcus)

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17
Q

What are the common features under a microscope between Vibrio and Campylobacter?

A

Both of them are curved rods G- bacilli.

18
Q

List 4 characteristic features of the Genus Campylobacter.

A
  1. Seagull shape
  2. Best grown at 42 degrees (thermophilic)
  3. requires less O2 (microaerophilic)
  4. Shows silver tear-drop colonies on Skirrow agar
19
Q

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

A

E: not necessary!!

TCBS for differentiating sucrose fermenter or not!
Sucrose fermenter = yellow =
Vibrio cholerae

green = -ve, V.parahaemolyticus

20
Q

Campylobacter is spread via ________ reservoir.

A

poultry

21
Q

Name the 3 species of Vibrio and their clinical manifestations. (6)

A
  1. Vibrio cholerae: cholera
  2. Vibrio parahaemolyticus: GE
  3. Vibrio vulnificus: necrotizing fasciitis
22
Q

Other than self-limiting bloody diarrhea, what are the 2 other clinical manifestations of infections by Campylobacter?

A
  1. Reactive arthritis

2. Post-infection (more prone to?): Guillain Barre Syndrome

23
Q

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)

A

Black - H2S positive (either salmonella or proteus, but proteus does not cause diarrhea)
Yellow agar - non-lactose fermenter

Salmonella gastroenteritis!!!!
(NOT SALMONELLA)

24
Q

What is the management plan for Salmonella gastroenteritis? (2)

A

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

25
Q

50/F housewife presented with vomiting, diarrhea and abdominal pain without fever. The stool was watery and loose. Later on the same day, 2 other family members were also affected. The whole family had a seafood feast at home the night before.

DCA - remains red
TCBS medium - green

Green = ?
Probable species?
What is the oxidase reaction of this species?
Is it halophilic? (salt-loving)

A

Vibrio parahaemolyticus - sucrose non-fermenter

  • oxidase positive
  • Yes, it is halophilic.
26
Q

What advice would you give to a patient who had V.parahaemolyticus after a seafood meal to prevent further episodes?

A

Cook seafood thoroughly

Personal hygiene - wash hands before eating

27
Q

50/F housewife presented with vomiting, diarrhea and abdominal pain without fever. The stool was watery and loose. Later on the same day, 2 other family members were also affected. The whole family had a seafood feast at home the night before.

DCA - remains red
TCBS medium - green

What is the ddx if the patient had traveled outside HK and was more dehydrated and sick? Is it a notifiable disease? Why?

A

Cholera by Vibri cholerae

Yes, because a large scale outbreak is possible

28
Q

Michael, aged 4, had a beefburger. He developed watery diarrhea. By the 3rd day of illness, he had bloody diarrhea together with abdominal cramps. He developed fever and leukocytosis.

What do you expect to see on a MacConkey agar and on a sorbitol MacConkey agar?

A

MacConkey agar: red (lactose fermenter)
sorbitol MacConkey agar: yellow = non-sorbitol fermenter - in EHEC (most other serotypes of E.coli are sorbitol fermenters)

29
Q

Michael, aged 4, had a beefburger. He developed watery diarrhea. By the 3rd day of illness, he had bloody diarrhea together with abdominal cramps. He developed fever and leukocytosis.

What is the most likely organism?
What toxin does it produde?
What is the most important serotype?

A

EHEC

  • Enterohemorrhagic Escherichia coli
  • Most important: O157:H7 (causing HUS)
  • Shiga-like toxin-producing

another important serotype:
2011 O104:H4 - sprouts

30
Q

What is the mainstay of therapy in EHEC infection?

A
  1. Fluid rehydration
  2. Renal replacement
  3. Transfusion
  • Abx is not given, may worsen HUS!
  • no antitoxin for Shiga-toxin
31
Q

Do you have to report a case of EHEC infection? What advice would you give Michael parents, regarding their 2 month-old baby daughter?
(hamburger case)

A

Due to an epidemic potential, food substance shall be traced upon reporting the infection, is of public health concern.

Advice:

  • Cook food thoroughly (undercooked meat)
  • Separate meals for the 2-month-old baby to avoid cross-contamination
32
Q

25/M admitted due to severe abdominal pain and blood-stained diarrhea. He had taken a chicken dish at fast-food shop. One day before admission he complained of headache, fever, and pain over the limbs.

There are pure isolated white colonies of 1mm in diameter with irregular border (tear drop shaped).
Possible causative organism?

There is colonies growth on DCA as well and the color is red. Are you interested in this result?

A

Campylobacter jejuni (slow growing on Skirrow’s medium)

No, red = lactose fermenter (not Shigella, not Salmonella…)

33
Q

What do you expect to see in the Gram stain of Campylobacter?

A

Gram - seagull shaped bacilli

34
Q

A young man presented with upper abdominal tenderness. The patient was febrile and toxic with leukocytosis. (WCC: 14x 10^9)
CT scan of liver showed a lesion. The lesion is then aspirated and cultured.

Possible diagnosis?
What are the possible causative organisms?

A

Liver abscess *always a mixed picture - polymicrobial

  • Klebsiella
  • Peptostreptococci

(aerobes + anaerobes > aerobes use up O2 and favours anaerobes such as bacteroides)

35
Q

Treatment plan for liver abscess?

A
  1. Drainage of pus

2. Antibiotics with aerobic, anaerobic, and Klebsiella coverage.

36
Q

30/M factory manager who always works abroad presented with malaise, weight loss, low grade fever and profuse watery diarrhea for about 10-15 times a day. No bacterial pathogen was isolated for 3 times. At colonoscopic examination, ulcerative lesions were found.
Ziehl-Neelsen (ZN) stain was done on thin film of stool.

What is the possible causative agent? Where is the likely source?

A 
Cryptosporidium species (parasite)
- source: fecal oral route, ingestion of cysts in contaminated water
37
Q

30/M factory manager who always works abroad presented with malaise, weight loss, low grade fever and profuse watery diarrhea for about 10-15 times a day. No bacterial pathogen was isolated for 3 times. At colonoscopic examination, ulcerative lesions were found.
Ziehl-Neelsen (ZN) stain was done on thin film of stool.

What is the likely cause of his ulcerative lesion?

A

Amoebic/TB/ Crohn’s disease

38
Q

Renal unit 37/M presented to renal unit for watery diarrhea for several days, 10 water stools on the day of admission. On haemodialysis for the past 10 years. Completed a course of ampicillin 4 days prior to present admission for a chest infection.
He was afebrile and found to have a diffusely tender abdomen and increased bowel sounds. Rectal examination revealed soft green faeces.

Colonoscopic examination: nodular surface of the gut mucosa.

What is the patient suffering from?

A

Post-antibiotic colitis

  • Abx disrupts intestinal wall > invasion by Clostridium difficile
  • pseudomembranous colitis
39
Q

Culture of patient’s stool with C.difficle - any growth on aerobic/anaerobic blood agar?

A

Only on anaerobic agar.

40
Q

What methods can be used to confirm the etiology of diarrhea after the colonoscopy of a patient with colitis?

A
  1. Gold standard:
    Cell culture - presence of cytopathic effect due to the presence of toxins

(toxins destroy the cytoskeleton of cells, thus cells changes from elongated to rounded )

  1. ELISA kit for toxin assay
  2. PCR to detect toxin A/B
41
Q

What antibiotics is given to patients with C.difficle infection? (2)

A
  1. Vancomycin PO

2. Metronidazole PO

MICBI - Clinical MICBI (19 decks)

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