Quantitative PCR enumeration of and 16S rRNA type A and B genes as virulence indicators for environmental and clinical strains of in Galveston Bay oysters.

Oysters from a reef in Galveston Bay, Texas, USA, were screened for more virulent clinical strains versus less virulent environmental strains of using a combination of quantitative PCR assays for the virulence correlating gene (clinical variant, ) and 16S rRNA types A and B (type A = environmental, type B = clinical). The combination of and 16S rRNA type B loci to determine clinical type strains was suitable, as indicated by the strong correlation ( = 0.98; < 0.001) between these gene counts over time and their relative proportion (up to 93.8% and 94.3%, respectively) to genes used to quantify all strains of A strong seasonal shift of strain types was observed. Environmental strains (16S rRNA type A) predominated from April to mid-June as salinities increased from 22 to 27 PSU (practical salinity unit) and temperatures rose 20 to 28 °C, with peak gene quantities of 16 812 ± 56 CFU/g. As temperatures increased to ≥30 °C from mid-June to September and salinities rose above 27 PSU, clinical strains (16S rRNA type B; ) predominated with peak quantities 31 868 ± 287 and 32 360 ± 178 CFU/g, respectively.