Les Escherichia Coli potentiellement pathogenes dans l’environnement littoral : cas des STEC et des EPEC

The contamination of coastal areas by potentially pathogenic enteric bacteria is of concern for the sustainability of some uses, such as shellfish farming, recreational shellfish harvesting and bathing. The contamination of these environments may occur through the land-spreading of livestock wastes, animal feces deposited on pastures, wastewaters from slaughterhouses or from municipal wastewater treatment plants. The presence of these bacteria in coastal environment may present a potential risk to human health. In fact, shellfish-borne outbreaks or human infections may occur by the consumption of shellfish from contaminated areas or the ingestion of water during bathing in contaminated waters, respectively. To date, few studies focusing on the presence and the diversity of enteric bacteria, such as pathogenic Escherichia coli (E. coli) in coastal environments and shellfish have been reported. The PhD project aimed to (i) evaluate the presence of pathogenic E. coli, more precisely, Shiga toxinproducing E. coli (STEC) and enteropathogenic E. coli (EPEC) in shellfish-harvesting areas and their upstream catchments, (ii) characterize the diversity of isolated STEC and EPEC, (iii) estimate the molecular risk assessment by screening 75 E. coli virulence-associated gene targets and then (iv) evaluate the contamination and depuration of oysters in contact with STEC. For this purpose, during a 2-year study (February 2013 to January 2015), shellfish batches (n=238), freshwater (n=216), seawater (n=12), and surface sediment (n=39) samples from three selected shellfish-harvesting areas and their upstream catchments, were monthly analyzed to evaluate the presence of STEC and EPEC strains. Five percent of samples were positive for the isolation of at least one STEC and 14% for the isolation of at least one EPEC. Twenty-eight STEC and 89 EPEC strains were isolated representing 1% of the total E. coli (n=12 016). The isolated STEC and EPEC strains belonged to a high diversity with 75 different serotypes, 79 distinguishable PFGE patterns and 46 distinguishable sequence types. STEC and EPEC strains were distributed into to 15 and 55 virulence profiles, respectively. One STEC strain isolated from a mussel batch, belonging to the serotype O26:H11 stx1+eae+ displayed 45 additional virulence genes among the 75 investigated genes. Seventyfive percent of EPEC strains displayed between one and 19 virulence genes associated with pathogenicity islands specific to pathogenic E. coli involved in human infections. No difference in the kinetics of the contamination and depuration of oysters by STEC and non-STEC E. coli was found. To our knowledge, this study is the first to focus on the diversity of STEC and EPEC strains isolated from coastal environments. This study highlights the weak presence of STECs and EPECs in the French shellfish-harvesting areas studied and a potential pathogenicity of some strains. The low prevalence of STEC and EPEC strains in shellfish from B- and C-categories (depuration of shellfish before commercialization), as well as the decontamination of shellfish by STEC, fast and similar to that of non-pathogenic E. coli, is rather in favor of a limited risk of contamination of shellfish by STEC in the studied areas. The results obtained during this study are important to better understand the health risk associated with STEC and EPEC in coastal areas.