Salmonella and Shigella

Question 1

Features of Enterobacteriaceae family:

Answer 1

Gram negative bacilli
Facultative anaerobes
Glucose fermenters
cytochrome c oxidase negative
Reduce nitrates to nitrites

Question 2

The pathogenic genera in Enterobacteriaceae family are:

Answer 2

Shigella
Salmonella
Some strains of Escherichia

Question 3

The non-lactose fermenters in Enterobacteriaceae family are:

Answer 3

Shigella
Salmonella
Proteus

Question 4

Enteric fever is caused by which serotypes?

Answer 4

Salmonella Typhi
Salmonella Paratyphi A, B, and C

Question 5

Salmonella food poisoning or enterocolitis is caused by which serotypes of Salmonella?

Answer 5

S. Typhimurium
S. Enteritidis

Question 6

Septicemia with metastatic abscess is caused by:

Answer 6

Salmonella Choleraesuis

Question 7

Morphology of Salmonella genus.

Answer 7

Gram negative
motile
non-capsulated bacilli

Question 8

Cultural characters of Salmonella

Answer 8

Facultative anaerobes
They grow on simple media.
They produce pale non-lactose fermenting (yellow colorless) colonies on MacConkey and DCA

Question 9

Pathogenesis of enteric fever

Answer 9

1- Infection begins in small intestine
2- Organism multiplies in mesenteric lymph nodes
3- Then passes through lymphatics to blood stream causing primary bacteremia which lasts for one week
4- Then it spreads through phagocytic cells to some organs and multiplies there.
5- It then passes to blood causing secondary heavier bacteremia with signs of clinical illness and fever.

Question 10

Clinical manifestations of enteric fever

Answer 10

Fever, Malaise, Headache
Delirium
Tender abdomen
Constipation
enlargement of spleen

Question 11

Complications of enteric fever

Answer 11

Intestinal hemorrhage and perforations

Question 12

Diagnosis of enteric fever

Answer 12

During first week: Isolation from blood.
In the second week and onward: Isolation from stools and urine.
Serological tests include Widal test
Carriers of S. Typhi have Vi agglutinins in their sera.

Question 13

Prevention against enteric fever

Answer 13

1- Sanitary measures
2- Vaccines
3- Carriers must not be allowed to work as food handlers

Question 14

Pathogenesis of food poisoning/Salmonella Enterocolitis

Answer 14

The pathogen invades and replicates in epithelial cells of small and large intestine leading to intestinal lesions and diarrhea.
The incubation period is 12-48 hours

Question 15

Manifestations of food poisoning

Answer 15

nausea, vomiting
abdominal discomfort
severe diarrhea
slight fever

Question 16

Diagnosis of Salmonella Enterocolitis

Answer 16

The organism can be isolated from stools
Blood cultures are negative

Question 17

Morphology of Shigella genus

Answer 17

Gram negative bacilli
non-motile
non-capsulated

Question 18

Cultural characters of Shigella genus

Answer 18

They produces pale non-lactose fermenting colonies on MacConkey’s medium and DCA
On TSI agar they cause alkaline slant and acid butt

Question 19

Serological characters of genus Shigella

Answer 19

They are divided into 4 serogroups according to O antigen:
Group A: Sh. dysenteriae includes 13 serotypes
B: Sh. flexneri - 8 serotypes
C: Sh. boydii - 18 serotypes
D: Sh. sonnei - one serotype

Question 20

Virulence factors of genus Shigella

Answer 20

Invasiveness
Shiga toxin

Question 21

Shigellosis pathogenesis

Answer 21

Invasion of the mucosa and wall of large intestine and terminal ileum leading to necrosis, superficial ulcers, pseudo-membrane formation, and bleeding.
No blood invasion
Incubation period is 1-4 days

Question 22

Clinical manifestations of shigellosis

Answer 22

abdominal pain
diarrhea, dysentery, and tenesmus
fever

Question 23

Diagnosis of shigellosis

Answer 23

Macroscopic examination to detect blood and mucus
Microscopic examination reveals pus and RBCs
Stool examination