Extended-spectrum β-lactamases in Shigella flexneri from Argentina: first report of TOHO-1 outside Japan

A 9-year nation wide survey of the presence of extended-spectrum β-lactamases (ESBLs) in Shigella flexneri is described. Ten of 9033 (0.1%) isolates produced ESBLs, which were characterized by isoelectric focusing, PCR and DNA sequencing. These were CTX-M-2 (five isolates), TOHO-1 (one isolate), SHV-2 (two isolates) and PER-2 (two isolates, the first report in S. flexneri world wide). The emergence of each ESBL type in S. flexneri was not restricted to a particular region of Argentina. TOHO-1 showed a more basic isoelectric point (8.4) than that previously found (7.8) and its encoding gene (blaTOHO-1a) harboured a silent change, G825A, relative to the reported blaTOHO-1. All the ESBL-encoding genes were transferred to Escherichia coli by conjugation. PFGE analysis indicated that the 10 ESBL-producing S. flexneri isolates were subtypes of a unique clone.