SmeDEF-mediated antimicrobial drug resistance in Stenotrophomonas maltophilia clinical isolates having defined phylogenetic relationships.
OBJECTIVE
To test whether smeDEF overexpression leads to a predictable multi-drug resistance phenotype in Stenotrophomonas maltophilia and to measure the frequency with which smeDEF overexpression occurs in clinical isolates and in spontaneous drug-resistant mutants.


METHODS
Overexpression of smeDEF was induced in clinical isolates by the introduction of chromosomal mutations in smeT using a gene-replacement approach. Spontaneous drug-resistant mutants were selected using greater than MIC concentrations of various antimicrobial agents. Levels of smeE and smeF mRNAs were quantified using RT-PCR; MICs were determined using Etest.


RESULTS
Of 20 spontaneous S. maltophilia drug-resistant mutants tested, four overexpressed smeDEF, but only two carried mutations within smeT. Of 30 clinical isolates tested, 6 significantly overexpressed smeDEF. One of these had an IS1246-like element embedded within the putative SmeT binding site in the smeDEF promoter. All smeDEF overexpressing derivatives of an isolate had the same resistance profile; derivatives that did not overexpress smeDEF did not share this resistance profile. However, no consistent phenotype could be associated with smeDEF overexpression in S. maltophilia isolates per se.


CONCLUSIONS
SmeT is not the only gene product that affects smeDEF expression. IS element insertion is a viable mechanism by which smeDEF expression can be derepressed. There is evidence for a background-specific, predictable effect on resistance profile when smeDEF is overexpressed, but the variability of backgrounds encountered means no general SmeDEF-mediated phenotype can be defined. There is strong evidence for the existence of as yet unidentified multi-drug efflux pumps in this species.
Gould
Virginia C
VC
Bristol Centre for Antimicrobial Research and Evaluation, Department of Cellular and Molecular Medicine, School of Medical Sciences, University of Bristol, University Walk, Bristol BS8 1TD, UK.
Avison
Matthew B
MB
D000900:Anti-Bacterial Agents / Q000494:pharmacology; D001426:Bacterial Proteins / Q000235:genetics / Q000502:physiology*; D004251:DNA Transposable Elements / Q000235:genetics; D024901:Drug Resistance, Multiple, Bacterial / Q000235:genetics*; D005809:Genes, Regulator; D016905:Gram-Negative Bacterial Infections / Q000382:microbiology; D006801:Humans; D026901:Membrane Transport Proteins / Q000235:genetics / Q000502:physiology*; D008826:Microbial Sensitivity Tests; D016254:Mutagenesis, Insertional; D009154:Mutation; D011401:Promoter Regions, Genetic; D012329:RNA, Bacterial / Q000032:analysis; D012333:RNA, Messenger / Q000032:analysis; D012097:Repressor Proteins / Q000235:genetics; D020133:Reverse Transcriptase Polymerase Chain Reaction; D020615:Stenotrophomonas maltophilia / Q000187:drug effects* / Q000235:genetics
D000900:Anti-Bacterial Agents; D001426:Bacterial Proteins; D004251:DNA Transposable Elements; D026901:Membrane Transport Proteins; D012329:RNA, Bacterial; D012333:RNA, Messenger; D012097:Repressor Proteins; C417265:SmeD protein, Stenotrophomonas maltophilia; C417266:SmeE protein, Stenotrophomonas maltophilia; C417267:SmeF protein, Stenotrophomonas maltophilia