Using PCR-based detection and genotyping to trace Streptococcus salivarius meningitis outbreak strain to oral flora of radiology physician assistant

We recently investigated three cases of bacterial meningitis that were reported from a midwestern radiology clinic where facemasks were not worn during spinal injection of contrast agent during myelography procedures. Using pulsed field gel electrophoresis we linked a case strain of S. salivarius to an oral specimen of a radiology physician assistant (RPA). We also used a real-time PCR assay to detect S. salivarius DNA within a culture-negative cerebrospinal fluid (CSF) specimen. Here we extend this investigation through using a nested PCR/sequencing strategy to link the culture-negative CSF specimen to the case strain. We also provide validation of the real-time PCR assay used, demonstrating that it is not solely specific for Streptococcus salivarius, but is also highly sensitive for detection of the closely related oral species Streptococcus vestibularis. Through using multilocus sequence typing and 16S rDNA sequencing we further strengthen the link between the CSF case isolate and the RPA carriage isolate. We also demonstrate that the newly characterized strains from this study are distinct from previously characterized S. salivarius strains associated with carriage and meningitis.