Coxiella burnetii: Properties of the Bacteria

Coxiella burnetii

C. burnetii is the causative agent of Q fever, a zoonotic diseasetransmitted from animals to humans. Q fever was first studied in an experimental infection of guinea pigs by inoculation of blood from patients suffering from typhus-like fever to guinea pigs by Derrick in 1935. As the etiological agent of the disease was not known, the condition was referred to as query or Q fever. Subsequently, Burnett identified the causative agent as a rickettsial, after which the pathogen was named as Rickettsiaburnetii. Cox in the United States demonstrated the agent inticks and named it Rickettsia diaphorica. Later, both the rickett-sial strains were shown to be identical. The organism is now named as C. burnetii and reclassified in the group Protobacteria.

Properties of the Bacteria

◗ Morphology

burnetii shows following features:

·           C. burnetii is an obligate intracellular bacterium.

·           It is pleomorphic and measures 1 3 0.3 mm in size.

·      The bacterium is Gram negative, but stains poorly with Gram staining. These bacteria like other rickettsiae stain best with Giemsa or Gimenez stains.

◗ Culture

C. burnetii primarily infects the monocytic macrophage cell. Itmultiplies in phagolysosomes of the infected cell. It grows well in various cell lines and in the yolk sac.

◗ Other properties

Susceptibility to physical and chemical agents: Coxiellaaremost resistant pathogens to heat and dryness. They are not completely killed at 608C or by 1% phenol in 60 minutes. Hence, pasteurization by holding method is not effective method for killing C. burnetii, but the flash method is effective. The bacte-ria survive for a month in meat and for a year or more in dried feces at 48C.