Quantitative PCR Analysis of the Bartonella henselae carD Gene during Bacterial Stress
The Bartonella genus is comprised of arthropod-borne, intracellular bacterial pathogens that colonise the mammalian bloodstream. A large number of mammalian species are hosts for one or more Bartonella species, as either reservoir or incidental hosts. Bartonella species are only able to invade and replicate in host red blood cells in the reservoir host, and to be taken up by an associated haematophagous arthropod vector to complete transmission and the bacterial life cycle. Humans are the reservoir hosts for B. quintana and B. bacilliformis, and are incidental hosts for more than 16 additional zoonotic Bartonella species, including B. henselae, which is normally carried by cats. B. henselae infection, usually acquired through cat scratches or bites, can result in several clinical manifestations, with varying degrees of severity; the most common of these is cat scratch disease, where symptoms commonly range from enlarged lymph nodes to severe fever. Although usually a mild illness, B. henselae infection can occasionally lead to severe symptoms, affecting neurological and other major organ systems. During their life cycle the Bartonellae must adapt to various toxic host environments; such adaptation is mediated by several bacterial stress pathways, which modify bacterial transcription. However, many gaps remain in the understanding of B. henselae stress response pathways. The object of this study, the carD gene, was identified as a possible component of the Bartonella stress response. The carD gene has been shown to be critical for stress defence in other bacterial species, including Mycobacterium tuberculosis, Thermus thermophilus, and Myxococcus xanthus. Our study aimed to investigate whether carD played as significant a role during the B. henselae response to stresses as it does in other bacterial genera. We first attempted to perform growth comparisons between a B. henselae carD mutant strain and a wild type strain during exposure to stress conditions; however, our mutagenic carD plasmid interfered with bacterial growth of Escherichia coli cultures, which hindered transformation and generation of a B. henselae carD mutant. As an alternative, we investigated the expression of B. henselae carD under stress conditions, comparing carD expression during stress against a non-stressed B. henselae control, using quantitative PCR. We found no significant difference of expression of the carD gene between the control and any of our conditions, although a trend of increased carD expression was found in several stress conditions. We believe that these findings merit further study into the role of carD in the B. henselae stress response.