Stenotrophomonas maltophilia D457R contains a cluster of genes from gram-positive bacteria involved in antibiotic and heavy metal resistance

Abstract

A cluster of genes involved in antibiotic and heavy metal resistance has been characterized from a clinical isolate of the gram-negative bacterium Stenotrophomonas maltophilia. These genes include a macrolide phosphotransferase (mphBM) and a cadmium efflux determinant (cadA), together with the gene cadC coding for its transcriptional regulator. The cadC cadA region is flanked by a truncated IS257 sequence and a region coding for a bin3 invertase. Despite their presence in a gram-negative bacterium, these genetic elements share a common gram-positive origin. The possible origin of these determinants as a remnant composite transposon as well as the role of gene transfer between gram-positive and gram-negative bacteria for the acquisition of antibiotic resistance determinants in chronic, mixed infections is discussed.

FIG. 1

Analysis of the presence of mphBM in the genome of S. maltophilia D457R. The presence of this gene in the genome of S. maltophilia was analyzed by two different methods. (a) Results of PCR amplification with primers specific for mphBM. M, molecular size markers. Top, 200 bp; bottom, 100 bp; +, positive control, with amplification using the plasmid pERY1 as the template; lanes 1 and 2, amplification with two different genomic DNA preparations from S. maltophilia D457 as templates. A band with the predicted molecular size (144 bp) was amplified from both DNAs. −, negative control. (b) Results of the hybridization of EcoRI-digested genomic DNAs from S. maltophilia D457 (lane 1) and D457R (lane 2) with an internal probe specific for the detection of mphBM. In both cases, a hybridization signal corresponding to a 4.2-kbp DNA fragment was detected. M, molecular size markers. Bars, from the top: 23, 9.4, 6.5, 4.4, 2.3, and 2.0 kbp.

FIG. 2

Organization of the ERY1 region from S. maltophilia D457. The genetic structure of this region, as well as its relationship with some other previously analyzed sequences, is shown. The structure of ERY1 is shown in the middle of the figure. White arrows indicate the localization and orientation of the ORFs of the region. All of them present homologies of >90% with the previously characterized sequences shown in the figure. Black arrows indicate the localization and orientation of regions with homologies of >90% with sequences deposited at DNA data banks but which do not contain any ORFs. Gray arrows indicate the position and orientation of regions with homologies with sequences deposited at DNA data banks of <90%.