Bartonella

The Bartonella genus has grown from a single member in the early 1990s (i.e., Bartonella bacilliformis), to 31 validated species at this writing. Eleven species are considered to be aetiologic agents of emerging or re-emerging infectious diseases of humans. The widespread occurrence of Bartonella in mammalian reservoirs ranging from bats to whales, together with a broad spectrum of potentially life-threatening disease manifestations in infected hosts, has stimulated considerable research to elucidate the molecular pathogenesis, epidemiology and genetics of these bacteria. Bartonella share several general attributes. They are small (approximately 0.3µm in width by 1µm in length), Gram-negative, pleomorphic coccobacilli with a genomic GC content of ~40%. Bartonellae are facultative intracellular pathogens that employ haemotrophy (infection of erythrocytes) as a parasitic strategy. As such, their growth in vitro can only be accomplished in media containing blood or haem supplements, and even then they are notoriously fastidious and slow-growing. Arguably one of the most remarkable observations is that virtually every type of mammal surveyed has been found to serve as a host and/or reservoir for a subset of Bartonella species. Moreover, transmission of these bacteria is usually vectored through haematophagous arthropod ectoparasites of the host.