Bacterial Diseases > Coxiella burnetii and Q Fever

Biology of Coxiella burnetii

C. burnetii is a short, rod-shaped bacterium referred to as being Gram-negative, but which stains very poorly with Gram stain. It is an obligate intracellular pathogen in nature, replicating only inside cells. Recently, however, techniques have been developed to allow axenic or cell-free growth.

Within cells, the bacterium replicates inside membrane-bound structures called parasitophorous vacuoles. During the course of its development, two morphologically distinct forms of C. burnetii are observed:

In addition to morphological variants, C. burnetii also exists in two phase variants based on the structure of its surface lipopolysaccharide (LPS):

The type of LPS is the only virulence factor defined for C. burnetii. A full length LSP (phase I) is associated with an ability to induce disease in humans and animals, whereas Coxiella with a truncated LPS (phase II) do not usually cause disease in immunologically competent animals.

C. burnetii possesses a circular chromosome appoximately 2 Mbp in size. Nucleotide sequencing has led to classification of six genomic groups, referred to as I to VI. Additionally, all isolates of C. burnetii examined contain either an autonomously replicating plasmid or have plasmid sequences integrated into their chromosome. Again, there is genetic diversity in plasmid sequences and four distinct plasmid types have been characterized.

Overview of Coxiellosis (Q Fever)

Updated 2022; send comments to