FASTIDIUOS GRAM NEGATIVE RODS. PART 9

Question 1

What disease is caused by Yersinia pestis?

Answer 1

plague, also known as the black death.

Question 2

Which bacterial family does Yersinia pestis belong to?

Answer 2

Yersinia pestis is a member of the Enterobacteriaceae family.

Question 3

Which body part does the infection primarily affect?

Answer 3

The infection affects the lymph nodes, which can be found in the groin, neck, and armpits. These lymph nodes may enlarge and suppurate (form pus).

Question 4

How can the infection occur in humans?

Answer 4

Inhaling airborne droplets containing the organisms.
Handling infected rodents or domestic animals (such as cats and dogs) that harbor infected fleas.

Question 5

What are the biological vectors for Y. pestis

Answer 5

fleas
rodent

Question 6

How does the flea play a role in transmitting the infection?

Answer 6

1. The flea draws viable Y. pestis organisms into its intestinal tract, where they multiply.
2. Some Y. pestis in the flea is regurgitated when the flea feeds on its next blood meal, thus transferring the infection to a new host.

Question 7

What happens to a few bacilli after they are taken up by tissue macrophages?

Answer 7

1. After losing their capsular layer, a few bacilli are taken up by tissue macrophages.
2. Macrophages cannot kill Y. pestis and provide a protected environment for the bacilli.
3. Within the macrophages, the bacilli re-synthesize their capsular layer.

Question 8

What happens to the re-encapsulated organisms after leaving the macrophages?

Answer 8

1. The re-encapsulated organisms then kill the macrophage.
2. They are released into the extracellular environment, where they travel to draining lymph nodes.

Question 9

Explain the life cycle of Yersinia Pestis

Answer 9

Flea draws viable Y. pestis organisms into its intestinal tract, and they multiply.Some Y. pestis in the flea regurgitated
when the flea gets its next blood meal thus transferring
the infection to a new host.
A few bacilli are taken up by tissue macrophages after
they lose their capsular layer. Macrophages can’t kill Y.
pestis and provide protected environment for bacilli so
they can re-synthesize their capsular layer.
The re-encapsulated organisms then kill the
macrophage and are released into the extracellular
environment where they travel to draining lymph nodes

Question 10

which diseases are caused by Yersinia pestis

Answer 10

1. Bubonic plague
2. Pneumonic plague
3. Septicaemic plague

Question 11

What characterizes bubonic plague

Answer 11

1. It is characterized by high fever
2. Acute lymphadenitis (inflammation of the lymph nodes) with painful hemorrhagic swellings
   called buboes (Buboes: Painful, swollen, and hemorrhagic (bleeding) lumps in the affected lymph nodes). , usually in the groin area
3. Hemorrhages turn the skin black—hence the name Black
   Death
4. Markedly raised white cell count with neutrophilia

{buboes may also occur in the neck or armpits, depending on where the flea bite occurred.}

Question 12

what are the characteristics of pneumonic plague

Answer 12

1. If organisms move from the lymphatics into the circulatory system, septicemic plague develops
2. Characterized by hemorrhage and necrosis in all parts of the body, meningitis, and pneumonia
3. Rapidly fatal unless treated at an early stage
4. Pneumonic plague is highly infectious and can spread quickly in conditions of poverty and
   overcrowding
5. The sputum contains large numbers of plague bacilli and is often blood stained

Question 13

what are the characteristics of septicemic plague

Answer 13

1. Serious haemorrhagic condition in which large numbers of Y. pestis are present in
   the blood.
2. The organisms often seen in peripheral blood smears.
3. Buboes are usually absent.
4. There is a haemorrhagic rash.
5. Septicaemic plague is rapidly fatal

Question 14

Pathogenesis of yersinia pestis

Answer 14

1. Endotoxin
2. Exotoxin
3. Two antigens (V and W): V and W proteins allow organism to grow within cells.
4. An envelope (capsular) antigen that protects against phagocytosis.

Question 15

Morphology of yersinia pestis

Answer 15

1. Y. pestis is a small Gram negative, non-motile coccobacillus

Question 16

Laboratory diagnosis of yersinia pestis

Answer 16

Y. pestis is a small Gram negative, non-motile coccobacillus
* It is capsulated
* In smears from specimens, shows bipolar staining (safety pin appearance) when stained
with methylene blue , Giemsa or Wayson’s rapid stain
When seen in blood smears, it is extracellular.
* Smears should be methanol-fixed for 5 minutes

Question 17

Culture characteristics for yersinia pestis

Answer 17

1. Y. pestis is an aerobe and facultative anaerobe.
2. Temperature range 14–37 ºC with an optimum of 27 ºC.
3. Cultures should be incubated at room temperature.
4. Blood agar: Y. pestis grows well on blood agar, producing small shiny, nonhaemolytic colonies after 24–48 h incubation at room temperature.

Question 18

biochemical tests results on yersinia pestis

Answer 18

1. Catalase positive
2. Oxidase negative
3. A rapid easy to perform immunochromatographic strip test availableto detect
   specific antigen to Y. pestis in bubo aspirates and sputum in bubonic and pneumonic
   plague.

Question 19

Antimicrobial susceptibility

Answer 19

Streptomycin, tetracycline and chloramphenicol
* Strict quarantine for 72 hours.