Similarities between the genetic environments of blaCTX-M-15 in Escherichia coli from clinical and food samples from Spain and overseas travellers

Sir, We read with interest the recent article by Dhanji et al. on blaCTX-M-15 genetic environments. The authors found that up to 17% of overseas travellers returning to the UK with diarrhoea were faecal carriers of CTX-M-15-producing Escherichia coli isolates. The extended-spectrum b-lactamase (ESBL) producers detected belonged to phylogenetic group A (40%), group D (32%), group B2 (16%) and, less frequently, group B1 (13%). The majority (62%) of isolates harboured the genetic environment found internationally, with an intact copy of ISEcp1 located 48 bp upstream of blaCTX-M-15, and only eight (5%) showed the characteristic 24 bp ISEcp1 remnant of UK strain A. In 22 (15%) isolates a 545 bp ISEcp1 fragment truncated by IS26 in the opposite direction was found upstream of blaCTX-M-15, named as the 2c genetic environment in the Dhanji et al. study (Figure 1), and 10 of these isolates belonged to phylogenetic group A. As the authors commented, international travel has been found to be a significant risk for colonization with CTX-M ESBL producers and they associated genetic environments of blaCTX-M-15 with specific travel destinations. Nevertheless, the unknown previous colonization with CTX-M-15 producers was admitted as a limitation of the study. Recently, we have found CTX-M-15-producing E. coli that belonged to group A and sequence type (ST) 410, recovered from five urine samples from community non-related patients and two raw turkey samples between 2005 and 2007 in our area. Five of those seven isolates showed 81.2% similarity by PFGE clustering, including clinical and meat isolates. In our study, blaCTX-M-15 was co-transferred with other resistance markers in related IncF group plasmids and clustered in the same fragment. Of note, the genetic environment in all these isolates (GenBank accession number GU479916) was identical to that named 2c found in UK travellers (GenBank accession number HQ157353). None of our patients came from the Indian subcontinent, Afghanistan or Egypt, or had travelled to those countries, and the meat samples were purchased fresh in local stores. We agree with Dhanji et al. that the spread of E. coli producing CTX-M-15 is complex and diverse. The emergence of different pulsotypes of highly virulent B23 ST131 producing CTX-M-15 has contributed to international spread co-transferred with blaOXA-1, blaTEM, tet(A), catB3 and aac(6′)-Ib, but, additionally, dissemination within group A strains with low virulence could also occur.