Yersinia: Introduction, Classification Morphology, Pathogenicity, Lab Diagnosis, Treatment, and Prevention


Yersinia is a genus of bacteria that includes several species, some of which are pathogenic to humans. The most well-known species within this genus are Yersinia pestis, the causative agent of the bubonic and pneumonic plague, and Y. enterocolitica, a cause of gastrointestinal infections. Other species within the genus include Y. pseudotuberculosis and Y. frederiksenii.

They are gram-negative and rod-shaped, and they are typically found in soil, water, and animals. They are known for their ability to survive in a wide range of temperatures, pH levels, and other environmental conditions, which allows them to persist in a variety of settings.

Yersinia infections can be transmitted through contaminated food, water, or direct contact with infected animals or people. Symptoms of the infection can range from mild gastroenteritis to severe systemic illness, depending on the species involved and the patient’s immune status. Treatment typically involves antibiotics, and early diagnosis is important to prevent complications.


Yersinia are gram-negative rods that are generally 0.5-0.8 micrometers in diameter and 1.5-5 micrometers in length. They are typically motile, with a single polar flagellum, and are non-spore-forming.

Under a microscope, cells appear as straight or slightly curved rods, often arranged singly or in pairs. They are facultative anaerobes, meaning they can grow in both the presence and absence of oxygen.

One unique feature of bacteria is their ability to produce a surface protein called YadA, which can help them attach to and invade host cells.

Yersinia enterocolitica colony morphology on CLED agar of Urine Culture
Fig. Yersinia enterocolitica colony morphology on CLED agar of Urine Culture


Yersinia species are known to be pathogenic to humans and animals. The three most well-known pathogenic species are Y. pestis, Y. enterocolitica, and Y. pseudotuberculosis.

Y. pestis is the causative agent of bubonic, septicemic, and pneumonic plague. It is transmitted to humans through the bites of infected fleas or through direct contact with infected tissues or bodily fluids. The bacteria can multiply rapidly in the lymph nodes, causing inflammation and swelling, and can spread to other organs, leading to sepsis and potentially fatal complications.

Y. enterocolitica and Y. pseudotuberculosis are gastrointestinal pathogens that can cause symptoms such as diarrhea, abdominal pain, fever, and vomiting. In severe cases, these infections can lead to complications such as sepsis, reactive arthritis, and erythema nodosum, a skin rash. These bacteria are typically transmitted through contaminated food or water, or through contact with infected animals or people.

They are able to survive and replicate inside host cells, such as immune cells and intestinal epithelial cells. They use a variety of virulence factors, such as adhesins and toxins, to invade and manipulate host cells, evade the immune system, and cause tissue damage. In particular, Yersinia species are able to resist phagocytosis by host immune cells, which allows them to evade clearance and persist in the host.

Lab Diagnosis

The laboratory diagnosis of Yersinia infections involves a combination of clinical findings, bacterial culture, and laboratory testing.

Clinical symptoms: The clinical symptoms of Yersinia infections can vary depending on the species involved and the severity of the infection. Symptoms can include fever, abdominal pain, diarrhea, nausea, vomiting, and skin lesions.

Bacterial culture: They can be cultured from clinical specimens, such as blood, stool, or lymph nodes. Y. enterocolitica and Y. pseudotuberculosis can be cultured on standard media such as MacConkey agar or blood agar, while Y. pestis requires specialized media such as Russell’s viper venom agar. Culture can take several days to yield results.

Laboratory testing: Several laboratory tests can aid in the diagnosis of these infections. These include:

  • Gram stain: They are gram-negative rods and can be visualized on a Gram stain.
  • Biochemical tests: Yersinia species can be identified using a variety of biochemical tests, such as oxidase and catalase tests.
  • Serological tests: Serological tests can detect antibodies to Yersinia in the patient’s blood, indicating a current or past infection. These tests include indirect hemagglutination assay (IHA), enzyme-linked immunosorbent assay (ELISA), and Western blot.
  • Polymerase chain reaction (PCR): PCR can detect Yersinia DNA in clinical specimens with high sensitivity and specificity, and can be used to confirm the presence of the bacteria in culture-negative samples.
Gram Negative Rods of Yersinia enterocolitica
Fig. Gram Negative Rods of Yersinia enterocolitica

It is important to note that laboratory diagnosis of Yersinia infections can be challenging, as the bacteria can be slow-growing and may require specialized media for culture. Additionally, cross-reactivity with other gram-negative bacteria can complicate serological testing. Therefore, a combination of clinical symptoms, culture, and laboratory testing is often necessary for accurate diagnosis.

Yersinia in wet mount
Fig. Yersinia in a wet mount


The treatment of Yersinia infections depends on the species involved and the severity of the infection. Antibiotics are typically used to treat Yersinia infections, but early treatment is important to prevent complications and reduce the risk of mortality.

For Y. enterocolitica and Y. pseudotuberculosis infections, antibiotics such as trimethoprim-sulfamethoxazole, doxycycline, and fluoroquinolones are commonly used. In severe cases, hospitalization and intravenous antibiotics may be necessary.

For Y. pestis infections, antibiotics such as streptomycin, gentamicin, and doxycycline are effective, and treatment should be initiated as soon as possible to prevent severe complications. Patients with pneumonic plague may require respiratory isolation to prevent transmission to others.

In addition to antibiotics, supportive care such as fluid and electrolyte replacement may be necessary for patients with severe Yersinia infections.


Prevention of infections involves a combination of measures aimed at reducing exposure to the bacteria and controlling its transmission. Some strategies for preventing these infections include:

  1. Proper food handling: Y. enterocolitica and Y. pseudotuberculosis can be transmitted through contaminated food and water, so it is important to practice good food handling and hygiene practices, such as washing hands and utensils thoroughly, cooking food at safe temperatures, and avoiding cross-contamination between raw and cooked foods.
  2. Safe water supply: Ensure that the water supply is safe and free from contamination, especially in areas with a history of Yersinia outbreaks.
  3. Vector control: Y. pestis is transmitted through the bites of infected fleas, so measures to control flea infestations in animals and their environments can help prevent transmission.
  4. Personal protective measures: People working in high-risk occupations such as laboratory workers, veterinarians, and wildlife biologists should wear appropriate personal protective equipment when handling potentially infected materials.
  5. Vaccination: There is a vaccine available for Yersinia pestis, which is recommended for individuals at high risk of exposure, such as laboratory workers and military personnel.
  6. Public health measures: In the event of an outbreak or epidemic of these infections, public health measures such as quarantine, isolation, and contact tracing can help control the spread of the disease.


In general, Yersinia species have similar morphology, but they can vary slightly in size and shape. For example, Y. pestis cells are slightly larger and more robust than other Yersinia species, while Yersinia enterocolitica cells tend to be slightly curved or bent.

It is important to note that some strains of Y. enterocolitica and Y. pseudotuberculosis have developed resistance to certain antibiotics, so susceptibility testing is recommended to guide treatment. Additionally, antibiotic treatment alone may not be sufficient to control outbreaks of Yersinia infections, and public health measures such as quarantine and hygiene measures may also be necessary.

Overall, the prevention of Yersinia infections requires a multi-faceted approach, involving individual actions and public health measures.

Further Readings

  1. “Yersinia Infections.” Centers for Disease Control and Prevention. 14 January 2022.
  2. Bhaduri, Saumya and Johnathan G. Frye. “Yersinia enterocolitica: Epidemiology, Pathogenesis, and Diagnosis.” Current Clinical Microbiology Reports, vol. 4, no. 3, 2017, pp. 112-118.
  3. Perry, Robert D. and Frank R. DeLeo. “Yersinia pestis.” Annals of Emergency Medicine, vol. 71, no. 3, 2018, pp. 386-394.
  4. Singh, Pradeep and Ramandeep Singh. “Yersinia pseudotuberculosis: An Overview.” Microbiological Research, vol. 194, 2017, pp. 1-6.
  5. Tan, Lawrence K. and James W. McAuley. “Outbreak of Yersinia enterocolitica Infection.” Current Infectious Disease Reports, vol. 23, no. 3, 2021, pp. 1-8.
  6. World Health Organization. “Plague.” 22 February 2021.

1 thought on “Yersinia: Introduction, Classification Morphology, Pathogenicity, Lab Diagnosis, Treatment, and Prevention”

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