RESUMEN
A 7-year-old pregnant Angus cow was found dead in the field. At necropsy, the aortic valve was expanded by moderate fibrous connective tissue and acidophilic coagulum containing multifocal marked bacteria, mineral, neutrophils, and red blood cells. Numerous tiny grayish, opaque bacterial colonies were detected on blood agar plates at 7 days after inoculation with a swab of the heart valve of the cow. The bacterium was a Gram-negative, very small coccobacillus that was catalase, oxidase, and urease negative, and did not change litmus milk, triple sugar iron agar, and sulfide-indole-motility medium. The bacterium was negative for esculin hydrolysis, phenylalanine deaminase, nitrate reduction, and gelatin hydrolysis. The isolate did not produce acid from glycerol, inulin, lactose, maltose, mannose, raffinose, salicin, sorbitol, sucrose, trehalose, glycogen, ribose, or starch. Polymerase chain reaction tests for the gltA, ssrA, ftsZ, ribC, rpoB, and 16S ribosomal RNA genes of Bartonella species were positive for the isolate. Amplicons were sequenced, and the gltA, ribC, ssrA, and 16S ribosomal RNA gene sequences were found to have 100% homology to the type strain of Bartonella bovis, whereas the fts and rpoB sequences showed 99.9% and 99.6% homology, respectively, to the type strain of Bartonella bovis. Diagnosticians should be aware of slow-growing microorganisms, and culture media should be incubated beyond the standard period to enhance the recovery of Bartonella species.