Objective: To detect the 16S ribosomal RNA (rRNA) of 3 streptococcal species in the peripheral blood and synovial fluid of patients with psoriatic arthritis (PsA).
Methods: Reverse transcription-polymerase chain reaction (RT-PCR) detection targets bacterial 16S rRNA, which is present in bacteria at high copy numbers. The 3 species-specific primers for group A streptococci (GAS; Streptococcus pyogenes), group B streptococci (GBS; Streptococcus agalactiae), and Streptococcus pneumoniae were designed from the fragments of highly variable V2 regions of 16S rRNA. Total RNA was prepared from whole peripheral blood and joint fluid obtained from patients with PsA and rheumatoid arthritis (RA). All positive PCR reactions were then sequenced with a Pharmacia ALF DNA sequencing system.
Results: Our data in 19 PsA patients showed that 7 peripheral blood samples were positive for GAS (P = 0.006 versus GAS-positive RA patients [n = 0], by Fisher's exact test), and 2 were also positive for GBS. One synovial fluid sample from a PsA patient was positive for GAS. S pneumoniae was absent from all specimens. Seventeen patients with RA were PCR negative for the 3 streptococcal species. Peripheral blood from a patient with inflammatory bowel disease was positive for GAS.
Conclusion: The presence of GAS 16S rRNA in the peripheral blood and synovial fluid of patients with PsA supports the concept that PsA is a reactive arthritis to certain streptococci.