Detection of dextranase-producing gram-negative oral bacteria

Thirty-one strains of 23 gram-negative oral bacterial species were examined for dextran-degrading activity on agar plates containing blue dextran. One strain each of Capnocytophaga ochracea, Capnocytophaga sputigena, Prevotella loescheii, Prevotella melaninogenica and Prevotella oralis had detectable dextranase activity. The culture supernatants of P. melaninogenica and P. oralis cells contained dextranases of multiple sizes, but those of the other three species had a single size of enzyme. A 56-kDa dextranase was purified from the culture supernatant of P. oralis and the antiserum against the enzyme was prepared with a rabbit. The Ouchterlony test showed that the antibody reacted with the supernatants of both P. melaninogenica and P. oralis but not with the others. Dot-blot hybridization using the dextranase gene of Streptococcus mutans as a probe revealed that there was no significantly homologous sequence in the chromosomal DNA of the five species.