First isolation of Shiga toxin 1d producing Escherichia coli variant strains in shellfish from coastal areas in France

AIMS: This study was carried out to evaluate the presence of Shiga toxin-producing Escherichia coli (STEC) and E. coli O157:H7 in shellfish from French coastal environments. METHODS AND RESULTS: Shellfish were collected in six growing areas or natural beds (B category) and nonfarming areas (D category) from July 2002 to August 2004. PCR detection of stx genes was performed on homogenized whole shellfish and digestive gland tissues enrichments. STEC strains were detected by colony DNA hybridization using a stx-specific gene probe and E. coli O157 strains were additionally searched by immunomagnetic separation with O157-specific magnetic beads. Stx genes were detected in 40 of 144 (27.8%) sample enrichments from mussels, oysters or cockles, 32 of 130 enrichments (24.6%) were from B-category areas and eight of 14 (57.1%) from the D-category area. Five strains carrying stx(1) or stx(1d) genes and one stx negative, eae and ehxA positive E. coli O157:H7 were isolated from six of 40 stx-positive enrichments. No relation was found between the total E. coli counts in shellfish and the presence of STEC strains in the samples. CONCLUSIONS: The STEC strains of different serotypes and stx types are present in shellfish from French coastal environments. It is the first isolation of STEC stx1d strains in France. SIGNIFICANCE AND IMPACT OF THE STUDY: Shellfish collected in coastal environments can serve as a vehicle for STEC transmission.