Prevalence and diversity of extended-spectrum beta-lactamases in faecal Escherichia coli isolates from healthy humans in Spain.

Extended-spectrum beta-lactamase (ESBL)-producing Escherichia coli isolates were detected in seven of 105 faecal samples from healthy humans, from two Spanish cities, during 2007. In these isolates, five ESBLs were detected, CTX-M-14 (n = 2), CTX-M-1 (n = 2), CTX-M-32 (n = 1), CTX-M-8 (n = 1) and TEM-52 (n = 1). Both bla(CTX-M-14a) (surrounded by ISEcp1-IS903) and bla(CTX-M-14b) variants (included in an integron structure) were identified in this study. This is the first time that the bla(CTX-M-8) gene and ESBLs of the CTX-M-8 group have been found in Europe and Spain, respectively. Faecal E. coli of healthy humans therefore constitute a reservoir of bla(CTX-M) genes with different surrounding genetic elements.