Coccobacillus in the context of "Bordetella pertussis"

Yersinia pestis (Y. pestis; formerly Pasteurella pestis) is a gram-negative, non-motile, coccobacillus bacterium without spores. It is related to pathogens Yersinia enterocolitica, and Yersinia pseudotuberculosis, from which it evolved. Yersinia pestis is responsible for the disease plague, which caused the Plague of Justinian and the Black Death, one of the deadliest pandemics in recorded history. Plague takes three main forms: pneumonic, septicemic, and bubonic. Y. pestis is a facultative anaerobic parasitic bacterium that can infect humans primarily via its host the Oriental rat flea (Xenopsylla cheopis), but also through aerosols and airborne droplets for its pneumonic form. As a parasite of its host, the rat flea, which is also a parasite of rats, Y. pestis is a hyperparasite.

Y. pestis was discovered in 1894 by Alexandre Yersin, a Swiss/French physician and bacteriologist from the Pasteur Institute, during an epidemic of the plague in Hong Kong. Yersin was a member of the Pasteur school of thought. Kitasato Shibasaburō, a Japanese bacteriologist who practised Koch's methodology, was also engaged at the time in finding the causative agent of the plague. However, Yersin actually linked plague with a bacillus, initially named Pasteurella pestis; it was renamed Yersinia pestis in 1944.

Pasteurella multocida is a Gram-negative, nonmotile, penicillin-sensitive coccobacillus from the family Pasteurellaceae. Strains of the species are currently classified into five serogroups (A, B, D, E, F) based on capsular composition and 16 somatic serovars (1–16). P. multocida is the cause of a range of diseases in mammals and birds, including fowl cholera in poultry, atrophic rhinitis in pigs, and bovine hemorrhagic septicemia in cattle and buffalo. It can also cause a zoonotic infection in humans, which typically is a result of bites or scratches from domestic pets. Many mammals (including domestic cats and dogs) and birds harbor it as part of their normal respiratory microbiota.