Lecture 10 & 11 Shigella, Salmonella and Yersinia

Question 1

Describe the general properties of Shigella (6)

Answer 1

1. Metabolically inactive E.coli
2. Non motile
3. Dont ferment lactose
4. Doesnt produce gas from glucose
5. Highly infectious
6. Spreads rapidly under crowding and poor sanitation
7. Incubation period 1-4 days

Question 2

Describe the pathogenicity and process of Bacillary dysentry of Shigella

Answer 2

Shigella invade M cells and then epithelial cells lining the large intenstine. They then multiply in cytoplasm of epithelial cells and this provokes an inflammatory response. Shigella then kill them and causes area of destruction of mucosa (resulting in dysentry).

Question 3

Describe the pathogenicity and process of Enteric fever of Salmonella Typhi

Answer 3

Causes typhoid fever, incubation period 1-2 weeks.
S.typhi invade epithelial lining and replicates in macrophages; spreads to blood and then organs throughout body. Causes 4 week fever if untreated, fever due to endotoxins.

Question 4

How to prevent typhoid fever (4)

Answer 4

1. Proper sewage disposal
2. Maintenance of water supplies
3. Exclusion of carriers from food handling
4. Vaccination

Question 5

Describe the pathogenicity and process of gastroenteritis of Salmonella enterica subspecies enterica serovars

Answer 5

Most common salmonella infection, incubation period 12-48 hours.
Salmonella adheres to GIT mucosa via pili, and invades mucosal cells. Then multiplies in the mucosal cells and passes through epithelial cells to the lamina propria. Its replication here results in diarrhoea.

Question 6

What is a zoonoses

Answer 6

Disease of animals accidentally transmitted to humans, often by insects.

Question 7

Describe the pathogenicity and process of babonic plague of Yersinia pestis

Answer 7

Incubation period 1-6 days.
Y.pestis replicates in flea gut, flea bites human and replicates in the lymph nodes. Replicates in lymphatics and then the blood which causes haemorrhagic in many organs. Contains many virulence factors and has a high fatality rate.

Question 8

Describe the pathogenicity and process of gastrointenstinal disease of Yersinia enterocolitica

Answer 8

Transmitted through ingestion of infected milk, water or food (pork), incubation period 4-7 days.
Y.entercolitica crosses intenstinal barrier to reach mesenteric lymph nodes. This can cause enterocolitis or mesenteric lymphadentis. Symptoms are bloody diarrhoea, fever and abdominal pain.