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 165,311 bp 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.