[Evaluation of growth of clinical Clostridium difficile strains belonging to different PCR-ribotypes on chromID C. difficile Agar].

Introduction: Clostridium difficile is main reason of antibiotic-associated diarrhea in hospitalized patients. Diagnostic method for detection of Clostridium difficile infection (CDI) are limited to an enzyme immunoassays (EIAs), while the culture of toxigenic strains is still seen as the gold standard for the laboratory diagnosis. The aim of this study was to compare growth of C. difficile strains belonging to different polymerase chain reaction (PCR) ribotypes on new ChromID C. difficile Agar (CDIFF, bioMérieux, Marcy l'Etoile, France).

Materials and methods: One hundred thirty one of clinical C. difficile strains stored. in Anaerobic Laboratory were cultured on ChromID C. difficile Agar. Ten faecal samples were cultured on the same chromogenic medium and incubated at 37°C for 24 h under anaerobic conditions. Isolates were confirmed as C. difficile on the basis of well-known criteria. PCR-ribotyping was performed by visually comparison of patterns of PCR products of the 16S-23S rRNA intergenic spacer region. We examined the occurrence of beta-glucosidase gene, responsible for the dark color of the colony C. difficile on ChromID C.difficile Agar using a pair of primers: gluF (5'-AAGGT GTAAATTTAGGAGGTTGGTT-3') i gluR (5'-AGGTCCCAACTATCCC ATCC-3').

Results: Among ten C. dfficile isolates obtained from stool specimens one formed colorless colonies. We received 8 colorless isolates from 131 additional examined strains. All C. difficile isolates forming colorless colonies belonged to PCR ribotype 023. The prevalence of PCR-ribotype 023 was about 6%. We detected lack of beta-glucosidase gene in PCR-ribotype 023 isolates.

Conclusions: There are some C. difficile strains forming colorless colonies on ChromID C.difficile Agar. This appearance is important in routine diagnostic use this chromogenic culture medium.