Yersinia Pestis

Yersinia pesti is a gram-negative bacterium belonging to the genus of Enterobacteriaceae, which was first isolated and identified by Alexander Yersin during the pestis in Hong Kong in 1894. The bacterium is transmitted through rat flea bites or aerosols, causing glandular pestis, pulmonary pestis and septicemia pestis. The mortality rate before treatment is 75% -100%. It carries pathogenic components such as capsule FI antigen, virulence V/W antigen, and mouse toxin, and can survive for several months in cold environments, with strong infectivity. In history, the bacterium caused three world pandemics: the Justinian plague in the 6th century, the Black Death in Europe in the 14th century, and the Oriental pestis at the end of the 19th century. In 2014, scholars extracted DNA from medieval remains and confirmed that it is the common ancestor of modern strains. The prevention and control measures include rodent and flea control, vaccination, and the use of antibiotics such as streptomycin.

Figure 1. Yersinia Pestis. (Easterday W R, et al, 2012)

Features

Yersinia Pestis is a short gram-negative coccobacterium. The newly isolated strains are stained with methylene blue or Giemsa, showing strong staining at both ends and capsule (or envelope). In the lesion specimen and primary culture, it appears oval shaped. Growing in short chain arrangement in liquid culture medium. Aerobic and facultative anaerobic bacteria are best isolated at a temperature of 27-28 ℃. For initial isolation, animal blood, sodium sulfite, and other substances should be added to the culture medium to promote growth. After 48 hours of cultivation at 28 ℃ on a blood plate, the bacteria will grow into opaque, central raised, non hemolytic, and border like colonies, which are characteristic of this bacterium. After 24 hours of incubation in liquid medium, a flocculent precipitate gradually forms. Within 48 hours, a thin bacterial film is formed on the surface of the liquid, and vertical hyphae grow from the film to the bottom of the tube in the form of stalactites.

Figure 2. Structure of Yersinia Pestis. (Sebbane F, et al, 2020)

Detection

The inspection of Yersinia Pestis must strictly follow the management rules of virulent bacteria, and pay attention to prevent aerosol infection or flea bites. Animal experiments should have protective equipment, and the culture and equipment used in the experiment should be disinfected in a timely manner. Take the smear of the test material, fix it with methanol or alcohol ether mixture for 5-10 minutes, then carry out Gram or methylene blue staining, and observe the morphological characteristics of Yersinia Pestis under microscope. Inoculate the test material onto regular agar plates, gentian purple blood agar plates, and Hottinger agar plates. After incubating at 28 ℃ for 48 hours, observe the characteristics of the colonies, select suspicious colonies, smear, stain, and examine under a microscope. If necessary, inoculate the thick golden agar slope and broth for further identification through bacteriophage lysis, agglutination, or precipitation tests. When the first confirmed case of pestis is reported, guinea pig subcutaneous or skin rub inoculation test shall be conducted.

Conclusions

Yersinia pestis is still a huge threat, because it has good adaptability as the pathogen transmitted by fleas, and has a strong pool of immunosuppressive virulence factors. Its molecular strategy centers on the delivery of T3SS mediated effector proteins such as YopH, YopE, and YopJ, disrupting host signaling nodes (p130Cas/FAK, Rho GTPase, MAPK/NF - κ B pathway) to enable rapid systemic disease. Although modern antibiotics can effectively treat epidemics if used early, the continued presence of zoonotic hosts, the risk of antibiotic resistance, and their potential as biological weapons require continued vigilance. Continuous research on its pathogenesis and immunology is crucial for developing the next generation of vaccines and treatments to alleviate the persistent threat of this ancient scourge.