Yersinia pestis (Plague)

8,900views

00:00 / 00:00

Flashcards

Yersinia pestis (Plague)

of complete

Memory Anchors and Partner Content

External References

First Aid

2024

2023

2022

2021

Yersinia pestis

animal transmission p. 147

intracellular organism p. 125

External Links

Transcript

Watch video only

Yersinia pestis is a Gram-negative coccobacillus which belongs to a family of bacteria called the Enterobacteriaceae.

It causes a disease called plague, which is transmitted by rodents, mainly rats, as well as prairie dogs, and their fleas.

Plague is highly contagious, and there have been three major pandemics in human history - one of them, known as the Black Death, killed up to one-third of the European population. Yikes!

Now, Yersinia pestis has a thin peptidoglycan layer, so it doesn’t retain the crystal violet dye during Gram staining.

Instead, like any other Gram-negative bacteria, it stains pink with safranin dye.

On Wright-Giemsa and Wayson staining it has a bipolar staining which means that only the poles of the bacteria stain, and the rest of it remains unstained, so the bacteria look like safety pins under the microscope.

Alright, now Yersinia pestis is non-motile, non-spore forming, facultative anaerobic which means it can survive in both aerobic and anaerobic environments and facultative intracellular which means it can survive both inside and outside the cells.

It’s oxidase and urease negative which means it doesn’t produce these enzymes and catalase positive which means it produces an enzyme called catalase.

Also, it’s indole negative which means it doesn’t convert tryptophan into indole.

Yersinia pestis grows well on MacConkey agar, sheep blood agar, and chocolate agar.

MacConkey agar is used to identify if a bacteria ferments lactose or not, and it contains a pH sensitive dye and lactose.

So, if a bacteria ferments lactose, it means that it’s able to ferment lactose and produce acid which causes the pH sensitive dye to turn pink leading to formation of pink colonies.

Non-lactose fermenters, like Yersinia pestis, aren’t able to modify the PH sensitive dye, grow into colorless colonies.

Next, on sheep blood agar and chocolate agar, Yersinia pestis forms opaque, yellow colonies that look like fried eggs.

Finally, the triple sugar iron test, or TSI for short can be done to assess hydrogen sulfide production.

This medium contains three sugars - lactose, glucose and sucrose, as well as iron and a pH sensitive dye.

If the bacteria produces hydrogen sulfide, that reacts with the iron, and a black precipitate forms in the test tube.

Yersinia pestis doesn’t, so no precipitate forms.

Now, the pathogenesis of Yersinia pestis consists of two components - the transmission of bacteria from fleas and the host response to the bacteria.

First, fleas get infected with Yersinia pestis by feeding on a bacteremic host like rats, which then colonizes the flea midgut.

So, when the flea bites a human it regurgitates the bacteria into the bite wound.

So, once the bacteria gets inside the host, neutrophils and macrophages come to the wound site to kill the bacteria.

Summary

Yersinia pestis is a Gram-negative bacillus that grows well on blood, chocolate, and MacConkey agar. Its virulence factors include capsular antigen F1, which protects it from neutrophils, and Yops, which inactivates macrophages, as well as a siderophore which it uses for iron uptake. It produces a disease called plague, which has three forms - bubonic, septicemic, and pneumonic. Plague is diagnosed by identifying the bacteria in cultures from blood, bubo aspirate, and sputum or in a peripheral blood smear with Gram, Wright-Giemsa, or Wayson staining and also through serological tests and rapid antigen tests. Effective treatment of plague involves aminoglycosides like gentamicin and streptomycin.

Elsevier

Copyright © 2024 Elsevier, its licensors, and contributors. All rights are reserved, including those for text and data mining, AI training, and similar technologies.

Cookies are used by this site.

USMLE® is a joint program of the Federation of State Medical Boards (FSMB) and the National Board of Medical Examiners (NBME). COMLEX-USA® is a registered trademark of The National Board of Osteopathic Medical Examiners, Inc. NCLEX-RN® is a registered trademark of the National Council of State Boards of Nursing, Inc. Test names and other trademarks are the property of the respective trademark holders. None of the trademark holders are endorsed by nor affiliated with Osmosis or this website.

RELX