Molecular study of vancomycin-resistant enterococci isolated from humans and from food in a cattle-rearing area of France

OBJECTIVES: Study possible links between vancomycin-resistant enterococci strains isolated from human stool samples and from pork or poultry food products. METHODS: One hundred and eleven vancomycin-resistant enterococci strains (15 VanA and 96 VanC) were isolated from human stool samples and from pork or poultry food products. Characterization of the Tn1546-like element of the 15 VanA strains was realized by restriction analysis of PCR products and polymorphism study. The 96 strains of VanC phenotype (75 Enterococcus gallinarum and 21 Enterococcus casseliflavus) were analysed by pulsed-field gel electrophoresis (PFGE). RESULTS: In the study described here, polymorphism of the Tn1546-like element enabled the establishment of five groups. Groups III, IV and V were found only in human strains. Groups I and II were found to occur in strains isolated from humans and from food, suggesting a possible transfer of the Tn1546-like element. The isolates from Group I harboured the whole Tn1546 element. In Group II, the five strains possessed a novel Tn1546-like element, characterized by a single-nucleotide difference in the vanX gene and a deletion upstream from the nucleotide 164. Analysis by PFGE of the 75 E. gallinarum strains revealed 20 different patterns. One pattern was shared by isolates from pork food and human samples. None of the 21 E. casseliflavus strains tested was found to share similar PFGE patterns. CONCLUSIONS: Results tend to support the possible transfer of the Tn1546-like element between strains of VanA phenotype. Concerning VanC phenotype strains, the transfer was not demonstrated.