Objective: In 2001, as part of the SENTRY worldwide antimicrobial surveillance programme, Pseudomonas aeruginosa 86-14571A was isolated at a hospital in Rome from a cancer patient with a bloodstream infection. The isolate was resistant to all antibiotics except amikacin, and displayed an imipenem MIC of 64 mg/L that decreased to 8 mg/L in the presence of EDTA. The resistance determinant was investigated.
Methods: The resistant determinant was cloned in Escherichia coli using a shotgun cloning approach.
Results: Sequence analysis revealed the presence of a novel IMP-type metallo-beta-lactamase (MBL) gene, blaIMP-13. This encoded a protein displaying most identity to IMP variants: 93% and 92.3% identity, respectively, to IMP-8 and IMP-2 (previously identified in Italy). The protein had 19 amino acid changes from IMP-2 and 17 amino acid changes from IMP-8. The blaIMP-13 gene was found as a gene cassette in the first position of a class 1 integron. A 25 bp inverted repeat sequence IRi was identified 174 bp upstream of the class I integrase, which suggests that the integron is found on a Tn402-like transposon, or defective transposon derivative. This element, in turn, is located in the transposition locus (tnp region) of a Tn21 subfamily transposon that showed most identity to Tn5051, a transposon recently identified from a strain of Pseudomonas putida isolated in New York. Interestingly, the insertion point of the Tn402-like transposon and the sequence of the Tn5051-like genes were identical to those of the genetic element harbouring blaVIM-2 recently identified in Poland.
Conclusions: The resistance determinant of P. aeruginosa 86-14571A is a novel IMP-type MBL carried on a composite transposon responsible for wide geographical dissemination of MBL genes in Europe.