Prevalence and Characterization of Shiga Toxin-Producing and Enteropathogenic Escherichia coli in Shellfish-Harvesting Areas and Their Watersheds

Abstract

more strains formed a strong biofilm at 18 than at 30°C. Finally, more than 85% of analyzed strains were found to be sensitive to the 16 tested antibiotics. These data suggest the low risk of human infection by STEC if shellfish from these shellfish-harvesting areas were consumed.

Keywords: EPEC; MLST; PFGE; STEC; biofilms; shellfish; water.

FIGURE 1

Focused dendograms of XbaI PFGE patterns (PTs), characteristics and Sequence Types (STs) of 9 STEC O100:HNM (A) and the 13 major serotypes (B) isolated from freshwater (FW), shellfish (SF) [oyster (o), mussel (m), or cockle (c)] and superficial sediment (S), from the Brittany site (1) and the two Normandy sites (2 and 3). The similarity of PFGE profiles was compared and dendogram was created with the Bionumerics software 7.5 (Applied Maths, Belgium), using the band-based Dice unweighted-pair group method, using average linkages (UPGMA), based on 1% position tolerance. NT: non-typable, NM: non-motile, nd: not determined.

FIGURE 2

Biofilm formation by EPEC and STEC strains at low and high temperatures. Biofilms were formed on polystyrene in M9 medium supplemented with glucose (0.4% wt/vol) at 18°C (gray bars) or 30°C (dark bars) for 24 h and were stained with crystal violet, and the absorbance at 590 nm was measured. The results are the average of at least three biological replicates and the error bar represent the standard error. The results for the static biofilms formed at 18 and 30°C were compared using two-way analysis of variance (ANOVA) followed by a Bonferroni post hoc comparison. ^∗p < 0.05; ^∗∗p < 0.01; ^∗∗∗p < 0.001. ^astx2⁺, ^bstx1⁺, ^cstx1⁺-stx2⁺, ^dstx1⁺-stx2⁺-ehxA⁺-saa⁺, ^estx1⁺-eae⁺, ^feae⁺, ^geae⁺-ehxA⁺.