Small qnrB-harbouring ColE-like plasmids widespread in commensal enterobacteria from a remote Amazonas population not exposed to antibiotics

Abstract

Sir, After a decade since discovery, a variety of qnr-type plasmid-mediated quinolone resistance genes have been reported worldwide, especially in clinical isolates of Enterobacteriaceae.1 Recently, we found that qnr genes (mostly qnrB) were highly prevalent among commensal enterobacteria from healthy children living in resource-limited urban settings of Latin America.2 This unexpected finding could not be directly related with quinolone use, since these drugs are not prescribed in childhood. We then speculated that it could reflect a sustained adults-to-children transmission of enterobacteria within households (favoured by crowding and poor hygienic standards) and, possibly, a co-selection of the qnr-harbouring plasmids due to the presence of linked resistance determinants to antibiotics that are used in children. The latter explanation, however, was ruled out for the most prevalent qnr gene (qnrB19), whose dissemination was found to be related to a broad and interspecific diffusion of two small ColE-like plasmids harbouring this gene as the sole resistance determinant (plasmids pECC14-9 of 3.0 kb and pECY6-7 of 2.7 kb).3 Similar small QnrB19-encoding ColE-like plasmids have recently also been identified in various Salmonella enterica serovars of human and animal origin, both in Latin America4 (GenBank accession number GQ412195) and Europe,5 underscoring their role in the international dissemination of qnrB19 in clinical and veterinary settings....