Identification of resistance and susceptibility to cefotaxime in EHEC O121 strains isolated from an outbreak at two nurseries

Abstract

A Shiga toxin 2 producing enterohemorrhagic Escherichia coli (EHEC) O121: H19 was isolated from a 2-year-old child who attending a nursery. An EHEC O121 outbreak in two nurseries (A, B), involving a total of 17 infected persons including 12 children, was revealed through contact investigation. The symptoms of all infected persons were almost all mild, and no one developed the hemolytic uremic syndrome. The combination use of desoxycholate-hydrogen sulfide-lactose (DHL) and CHROMagar STEC as selective isolation media was employed for efficient fecal examination. Nursery A and nursery B were combined as one group after the outbreak in nursery A was confirmed. As a result, EHEC O121 infected persons were also detected in children from nursery B. The 17 strains of EHEC O121 obtained from the total population showed almost the same pulsed-gel electrophoresis (PFGE) pattern, suggesting that these strains were very closely related. However, 13 of these 17 strains obtained from nursery A were susceptible to cefotaxime, whereas the remaining 4 strains obtained from nursery B showed cefotaxime resistance. A cefotaxime resistant Escherichia coli (E. coli) O86 strain was isolated in the stool specimen from a child who had been infected with the cefotaxime resistant EHEC O121. Both the cefotaxime resistant EHEC O121 and E. coli O86 had the same drug resistant gene (bla(CTX-M-1) group). The child was the index case of these 4 later cases and had received no antibiotics therapy prior to the laboratory examination. These findings suggested the possibility that an EHEC O121 strain had acquired a drug resistant gene from E. coli O86 in the digestive tract of the child.