Reverse transcriptase—polymerase chain reaction (RTPCR) assay of the outer membrane protein A (ompA) gene of Rickettsia felis. A, RT/PCR assay with total mRNA and ompA primers set 1 (nucleotides 1—1860). Molecular sizes were determined by a 1-kb DNA ladder, Lane 1, genomic PCR; lane 2, RT/PCR product of R. felis RNA; lane 3, water; lane 4 PCR of R. felis RNA without RT (control for potential DNA contamination). Kbp = kilobasepairs. B, RT/PCR with total mRNA using primer set 2 (nucleotides 2788— 3837). Lane 1, RT/PCR product.