CTX-M-15-Producing Shigella sonnei Strain from a Czech Patient Who Traveled in Asia

Abstract

International travel has been recognized as an important factor in the diffusion of multiresistant bacteria, including organisms that produce extended-spectrum β-lactamases (ESBLs) (14, 15, 16). When followed by clonal spread and/or horizontal transfer of ESBL-encoding plasmids in new areas, it may contribute to the global “epidemiologic success” of particular ESBL types. This is probably the case for some of the CTX-M enzymes (e.g., CTX-M-15), a family of derivatives of natural β-lactamases of Kluyvera spp. (3, 12). Here we report the first identification of ESBL-producing Shigella sonnei in the Czech Republic, from a 31-year-old female who traveled to China, Nepal, and India in April and May 2006. Immediately after returning, she was admitted with diarrhea and vomiting to a regional hospital. S. sonnei was cultured from stool; the identification was performed by ENTEROtest 24 (Pliva-Lachema Diagnostika, Brno, Czech Republic) and Shigella sonnei Polyvalent D (Denka Seiken, Tokyo, Japan). The isolate was found to produce ESBL with the double-disk synergy test (10). MICs of various antimicrobials, determined by the CLSI microdilution method (5), showed a classical ESBL-mediated pattern of β-lactam resistance, including cefotaxime and ceftazidime (Table ​(Table1).1). The patient, not treated with antibiotics, recovered in 21 days. TABLE 1. Antimicrobial susceptibility of the S. sonnei isolate described here The isolate was subjected to mating with Escherichia coli A15 Rifr as previously described (8); cefotaxime- and rifampin-resistant transconjugants were obtained at a frequency of 10−4 per donor cell. Isoelectric focusing (2) revealed that both the S. sonnei isolate and its transconjugant expressed β-lactamases with pIs of 8.9 and 5.4, of which the pI 8.9 enzyme hydrolyzed cefotaxime and ceftazidime in the overlay assay (2). PCR with primers P1C and P2D, which are specific for blaCTX-M-1-like genes (8), followed by DNA sequencing, identified the enzyme as CTX-M-15, which is encoded by a gene identical to those originally reported (1, 11). Owing to the Glu240Gly mutation, CTX-M-15 belongs to the CTX-M enzymes with significant ceftazidime-hydrolyzing activity (7, 13). PCR and sequencing of the 5′ flank of blaCTX-M-15, carried out as described previously (1), showed an ISEcp1 element placed 48 bp upstream from the gene. Such a genetic arrangement, suggesting a single ISEcp1-mediated escape of blaCTX-M-15 from Kluyvera spp., has been found in enterobacteria from many countries (12), including India, where CTX-M-15 was identified originally (11). Plasmid replicon typing (4), performed with the transconjugant's DNA, revealed the presence of a sole FII replicon, characteristic for plasmids that are associated with the worldwide spread of blaCTX-M-15 genes (6, 9). However, in contrast to many molecules of that type (6, 9), the plasmid did not transmit any other resistance from the S. sonnei isolate (Table ​(Table1)1) apart from that to β-lactams (data not shown). This report documents the repeated importation of a CTX-M-15 producer to Europe, where organisms with the same context of blaCTX-M-15, mostly E. coli, have already been disseminating (12), also in the Czech Republic (J.H., J.E., M.G., and P.U., unpublished data). It demonstrates further that the ongoing flow of ESBL-producing bacteria between different regions, including their constant supply from high-prevalence areas, makes the control of their wide spread enormously difficult.