Molecular characterization of serotype G2 and G3 human rotavirus strains that have an apparently identical electropherotype of the short RNA pattern.

The literature is conflicting whether or not rotavirus strains with different G serotype have an identical electropherotype. This is a contentious but an important issue because large parts of molecular epidemiological studies of rotaviruses have been based on the conception that a single strain of rotavirus can be defined by a single electropherotype. Here, we examined in detail by reverse-transcription PCR genotyping, electropherotyping, sequencing, and genogrouping using RNA--RNA hybridization three human rotavirus strains isolated in India that had apparently identical electropherotypes although one strain was typed as P[4], G3 while the other two typed as P[4], G2. These three strains showed an identical electropherotype on 7.5% and 12.5% polyacrylamide gels, but co-electrophoresis on a 10% gel demonstrated that segment 8 of the P[4], G3 strain migrated more slowly than the cognate segment of the P[4], G2 strains. Genogrouping assay and nucleotide sequencing provided evidence for the hypothesis that the P[4], G3 stain was an intergenogroup reassortant in which a P[4], G2 strain of the DS-1 genogroup had acquired the VP7 gene from an yet-unidentified concurrently circulating G3 strain. While electropherotyping remains a valuable asset for molecular epidemiology of rotaviruses, this study underscores the importance of co-electrophoresis under different electrophoretic conditions when pinpointing subtle differences.