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Proteae: a reservoir of class 2 integrons?

OBJECTIVES
Our aim was to confirm with a large panel of clinical isolates that class 2 integrons are highly prevalent in Proteae and to analyse their genetic characteristics.


METHODS
Proteae (Proteus spp., Morganella spp. and Providencia spp.) isolates were collected from clinical samples during 2013 at Limoges University Hospital, France. The presence of class 1, 2 and 3 integrons was investigated by quantitative PCR. The presence of a stop codon in the intI2 gene was determined by Sanger sequencing. The gene cassette arrays of class 2 integrons were determined by PCR-RFLP and Sanger sequencing or next-generation sequencing when needed.


RESULTS
Of the 327 Proteae collected, 103 (31.5%) harboured a class 2 integron and 45 (13.8%) a class 1 integron. No class 3 integrons were detected. One functional IntI2 integrase was detected in a Morganella morganii isolate. Six different gene cassette arrays were detected. Four had already been described in the literature: dfrA1-sat2-aadA1 (72 isolates), dfrA1-catB2-sat2-aadA1 (17), sat2-aadA1 (6) and lnu(F), dfrA1, aadA1 (1). We identified two new gene cassette arrays: (i) a new variant of the dfrA1 gene cassette (one isolate; the one with the functional IntI2); and (ii) the array dfrA1-gcu115-sat2 harbouring the new gcu115 gene cassette with two ORFs encoding proteins of unknown functions (five isolates).


CONCLUSIONS
We showed a high frequency of class 2 integrons, as well as a diversity of gene cassette arrays, among Proteae. This work highlights that the Proteae tribe plays an important role as a reservoir of class 2 integrons.