Development and evaluation of a PCR-based assay for detection of Haemobartonella felis in cats and differentiation of H. felis from related bacteria by restriction fragment length polymorphism analysis.

The 16S rRNA gene of Haemobartonella felis was amplified by using universal eubacterial primers and was subsequently cloned and sequenced. Based on this sequence data, we designed a set of H. felis-specific primers. These primers selectively amplified a 1,316-bp DNA fragment of the 16S rRNA gene of H. felis from each of four experimentally infected cats at peak parasitemia. No PCR product was amplified from purified DNA of Eperythrozoon suis, Mycoplasma genitalium, and Bartonella bacilliformis. Blood from the experimental cats prior to infection was negative for PCR products and was greatly diminished or absent 1 month after doxycycline treatment. The overall sequence identity of this fragment varied by less than 1.0% among experimentally infected cats. By taking into consideration the secondary structure of the 16S rRNA molecule, we were able to further verify the alignment of nucleotides and quality of our sequence data. In this PCR assay, the minimum detectable number of H. felis organisms was determined to be between 50 and 704. The potential usefulness of restriction enzymes DdeI and MnlI for distinguishing H. felis from closely related bacteria was examined. This is the first report of the utility of PCR-facilitated diagnosis and discrimination of H. felis infection in cats.