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Yersinia Pestis (Black Plague)

Ear-scientist Pests with Plague Doctor Mask
Picmonic
Yersinia pestis is a gram negative coccobacillus that can cause pneumonia, septicemia, and the bubonic plague. This organism is widely believed to be responsible for the death of approximately one third of the European population between 1347 and 1353. Today, the reservoir for this organism is several species of rodents including the black-tailed prairie dog, commonly found in the Southwest region, and transmitted via the flea vector. There have been several incidents of human transmission in people exposed to these animals. Pathogenesis includes several factors that allow the bacteria to suppress and avoid the normal immune response including an anti-phagocytic polysaccharide capsule and anti-phagocytic F1 and VW antigens that inhibit macrophages. Yersinia pestis is known to proliferate inside lymph nodes, causing lymphadenopathy and buboes, most frequently involving the inguinal lymph nodes. The term buboes gave rise to the name the bubonic plague. The organism could also get into the lungs causing a severe pneumonia with symptoms of chest pain, dyspnea, and hemoptysis. If the organism gets into the bloodstream, it can cause septicemic plague with complications of disseminated intravascular coagulation (DIC). Widespread DIC causes destruction of the blood vessels and results in black cutaneous hemorrhagic lesions on the skin. Many historians believe these lesions gave rise to the name “Black Death.” 
16 KEY FACTS
CHARACTERISTICS
Gram-Negative
Graham-cracker Negative-devil

This organism stains Gram-negative due to the relatively thin peptidoglycan layer in the cell wall.

Bacilli
Rod

These bacteria are small and sometimes described as resembling coccobacilli, but they are actually rods.

Oxidase-Negative
Ox-daisy Negative

The oxidase test is used to determine if a bacterium produces certain cytochrome c oxidases in order to use oxygen for energy production. Yersinia pestis is oxidase-negative, meaning it does not use the electron transport chain to make energy.

Non-lactose Fermenting
Nun Milk-carton Ferns

Yersinia pestis is characterized as a lactose nonfermenter because it cannot utilize lactose sugars in culture. The bacteria grows as white or colorless colonies on MacConkey agar, which is used to test for lactose fermenting capability.

Prairie Dogs
Prairie Dog

Today, the reservoir for this organism is several species of rodents, including the black-tailed prairie dog.

Fleas
Fleas

Today, the reservoir for this organism is several species of rodents. This includes the black-tailed prairie dog, commonly found in the Southwest region, and transmitted via the flea vector.

Polysaccharide Capsule
Polly-sack Capsule

Yersinia pestis has a polysaccharide capsule as a virulence factor, which aids in evading phagocytosis.

Vw Antigen
VW-car with Ant-Gem

Vw antigen is an antiphagocytic virulence mechanism that aids in the pathogenesis of Yersinia pestis.

F1 Antigen
(F1) Formula 1 Car Ant-Gem

F1 antigen is an antiphagocytic virulence mechanism that aids in the pathogenesis of Yersinia pestis.

Inhibits Macrophages
Inhibiting-chains on Mac-men

This bacterium has several antiphagocytic mechanisms, including a polysaccharide capsule, F1 antigen, and Vw antigen that inhibit phagocytosis by macrophages.

Southwest Region
Southwest scenery and cacti

The rodents that act as a reservoir for this organism are commonly found in the Southwest region of the United States.

SIGNS AND SYMPTOMS
Lymphadenopathy
Lymph-lime-add (+)

Yersinia pestis is known to proliferate inside lymph nodes, causing lymphadenopathy.

Pneumonia
Nude-Mona

In the lungs, Yersinia pestis can cause a severe pneumonia, with symptoms of chest pain, dyspnea, and hemoptysis.

Black Cutaneous Hemorrhagic Lesions
Black Skin Lesions

If the organism gets into the bloodstream, it can cause septicemic plague with complications of disseminated intravascular coagulation (DIC). Widespread DIC causes destruction of the blood vessels, and results in black cutaneous hemorrhagic lesions on the skin. Many historians believe these lesions gave rise to the name “Black Death.”

Buboes
Blue-bow

Yersinia pestis is known to proliferate inside lymph nodes, causing lymphadenopathy and buboes, most frequently involving the inguinal lymph nodes. The term buboes gave rise to the name the bubonic plague.

DIAGNOSIS
Bipolar Giemsa Staining
Pole with Gems

When tested with giemsa staining,Yersinia pestis has a bipolar staining pattern. This is due to the ends of the bacterium taking up more stain than the center of the organism.

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