Phenotypic and genotypic characterization of Pediococcus strains isolated from human clinical sources

Seventy-two strains of pediococci isolated from human clinical sources were characterized by conventional physiological tests, chromogenic enzymatic tests, analysis of whole-cell protein profiles (WCPP) by sodium dodecyl sulfate-polyacrylamide gel electrophoresis, and analysis of chromosomal DNA restriction profiles by pulsed-field gel electrophoresis (PFGE). Conventional tests allowed identification of 67 isolates: 52 strains were identified as Pediococcus acidilactici, 15 strains were identified as Pediococcus pentosaceus, and 5 strains were not identified because of atypical reactions. Analysis of WCPP identified all isolates since each species had a unique WCPP. By the WCPP method, the atypical strains were identified as P. acidilactici (two strains) and P. pentosaceus (three strains). The chromogenic substrate test with o-nitrophenyl-beta-D-glucopyranoside differentiated all 54 strains of P. acidilactici (negative reactions) and 13 (72%) of 18 strains of P. pentosaceus (positive reactions). Isolates of both species were shown to be nonclonal as revealed by the genetic diversity when chromosomal DNA was analyzed by PFGE. Using WCPP as the definitive identification procedure, P. acidilactici (28 of 54 strains; 51.8%) was more likely than P. pentosaceus (4 of 18 strains; 22.3%) to be isolated from blood cultures.