Entire sequence of the colonization factor coli surface antigen 6-encoding plasmid pCss165 from an enterotoxigenic Escherichia coli clinical isolate

•We isolated the CS6-encoding plasmid pCss165 of ETEC clinical isolate.•Virulence factors such as heat-stable toxin and transporters were encoded on it.•AraC family transcriptional regulators were found but not affected CS6 expression.•Conjugative transfer region and toxin–antitoxin systems were also found.•These genes might contribute to the prevalence of CS6 among ETEC isolates. Coli surface antigen 6 (CS6) is one of the most prevalent colonization factors among enterotoxigenic Escherichia coli (ETEC) isolated in developing countries. Although it is known that CS6 is encoded by a plasmid, there are no reports on the sequence analysis of the CS6-encoding plasmid or genes exhibiting similar behavior to CS6. Here, we report the isolation of the CS6-encoding plasmid, pCss165Kan, from 4266 ΔcssB::kanamycin (Km) and its complete nucleotide sequence. This plasmid consisted of 165,311bp and 222 predicted coding sequences. Remarkably, there were many insertion sequence (IS) elements, which comprised 24.4% of the entire sequence. Virulence-associated genes such as heat-stable enterotoxin, homologues of ATP-binding cassette transporter in enteroaggregative E. coli (EAEC), and ETEC autotransporter A were also present, although the ETEC autotransporter A gene was disrupted by the integration of IS629. We found that 2 transcriptional regulators belonging to the AraC family were not involved in CS6 expression. Interestingly, pCss165 had conjugative transfer genes, as well as 3 toxin–antitoxin systems that potentially exclude other plasmid-free host bacteria. These genes might be involved in the prevalence of CS6 among ETEC isolates.