Repetitive Sequence-based PCR Versus Pulsed-field Gel Electrophoresis for Typing of Enterococcus Faecalis at the Subspecies Level

Repetitive sequence-based PCR was compared to pulsed-field gel electrophoresis (PFGE) for the ability to discriminate Enterococcus faecalis isolates at the subspecies level. The BOXA2R primer, derived from repetitive sequences in Streptococcus pneumoniae, was applied to 41 isolates of E. faecalis collected from various sources. The REP1R-Dt and REP2-Dt primers, derived from the gram-negative repetitive extragenic palindromic element, were also applied to 18 selected isolates. Of the 41 isolates examined, 7 were beta-lactamase producing and 8 were vancomycin resistant. By PFGE, 17 isolates had distinct patterns; the other 24 were classified into eight different clonal groups. By PCR using the BOXA2R primer, 16 isolates generated distinct patterns; the other 25 were classified into nine different clonal groups. There were only minor differences in the PCR results obtained by using the BOXA2R primer and the REP1R-Dt and REP2-Dt primers. Two isolates among vancomycin-resistant enterococci from the greater Houston, Tex., area were related by PFGE, distinct by PCR with the BOXA2R primer, and related by PCR with the REP1R-Dt and REP2-Dt primers. Clonal relationships among the remaining 39 isolates were similar by both PFGE and PCR. PCR reliably discriminated all epidemiologically unrelated isolates. Although PCR is less time consuming than PFGE, PCR results were more difficult to interpret than PFGE results, perhaps because fewer bands were generated by PCR than by PFGE and some PCR products were inconsistently seen.