Coproduction of novel 16S rRNA methylase RmtD and metallo-beta-lactamase SPM-1 in a panresistant Pseudomonas aeruginosa isolate from Brazil

Abstract

Serious infections with Pseudomonas aeruginosa are frequently treated with the combination of a beta-lactam antimicrobial and an aminoglycoside. P. aeruginosa strain PA0905 was isolated in 2005 from an inpatient in Brazil. It showed a panresistant phenotype that included resistance to beta-lactams, aminoglycosides, and fluoroquinolones. The beta-lactam resistance was conferred by the production of the metallo-beta-lactamase SPM-1. No inhibitory zone was observed when a disk diffusion test was performed with the semisynthetic aminoglycoside arbekacin, raising suspicion of 16S rRNA methylase production. A cloning experiment subsequently revealed the presence of a novel 16S rRNA methylase, RmtD, which accounted for the high-level resistance to all 4,6-disubstituted deoxystreptamine aminoglycosides, such as amikacin, tobramycin, and gentamicin. RmtD shared a moderate degree of identity with RmtA, another 16S rRNA methylase that was initially reported to occur in P. aeruginosa in Japan in 2003. This is the first identification of aminoglycoside resistance mediated by a 16S rRNA methylase in South America. This is also the first report to document coproduction of a metallo-beta-lactamase and a 16S rRNA methylase, a combination that would severely compromise therapeutic options for the infected patients.

FIG. 1.

Schematic presentation of the genetic structure of the cloned regions containing rmtD. oriIS indicates the putative insertion site of transposition and its sequence. The lower sequence represents the consensus sequence of oriIS for IS91-related transposons.

FIG. 2.

Amino acid sequence of RmtD in comparison with those of known 16S rRNA methylases RmtA (GenBank accession number AB083212), RmtB (AB103506), RmtC (AB194779), and ArmA (AY220558).

FIG. 3.

Dendrogram of 16S rRNA methylases found in gram-negative bacilli, constructed with the ClustalW program provided by the Kyoto University Bioinformatics Center (http://align.genome.jp).