title: Clonal diversity and metallo-beta-lactamase production in clinical isolates of Stenotrophomonas maltophilia.
abstract: Stenotrophomonas maltophilia is a nosocomial pathogen with an intrinsic broad-spectrum resistance to beta-lactam compounds and other antibacterial agents. It produces two chromosomal beta-lactamases: a clavulanic acid-sensitive class A (L2) and a tetrameric carbapenemase (L1 or BlaS). We screened 40 S. maltophilia multidrug-resistant clinical isolates recovered between 1995 and 1998 in the Varese Hospital (Italy) for the presence of the metallo-beta-lactamase. The isolates were investigated by phenotypic profiling (enzymatic activity and antibiotic resistance pattern) and molecular methods such as PCR and pulsed-field gel electrophoresis (PFGE) to reveal intraspecies diversity. For the tested S. maltophilia strains, we showed that the beta-lactamase production could be induced by the presence of imipenem (50 microg/ml) in the culture media. Addition of 1 mM dipicolinic acid completely inhibited the hydrolysis of imipenem but decreased that nitrocefin in a strain-dependent manner. Full activity of crude extract towards imipenem could be restored by addition of 1 mM ZnCl2. Finally, the gene encoding the carbapenem-hydrolyzing beta-lactamase from S. maltophilia ULA-511 and 39/95, a clinical strain, were isolated and sequenced. These two strains have a different profile of multidrug resistance. The two metallo-beta-lactamases were found to be isologous. The difference of sensitivity of these two strains was associated to the level of production of the metallo-beta-lactamase.
mesh_terms: D000595:Amino Acid Sequence; D000900:Anti-Bacterial Agents / Q000494:pharmacology; D003001:Cloning, Molecular; D004352:Drug Resistance, Microbial; D016521:Electrophoresis, Gel, Pulsed-Field; D015378:Imipenem / Q000494:pharmacology; D008826:Microbial Sensitivity Tests; D008969:Molecular Sequence Data; D016133:Polymerase Chain Reaction; D017386:Sequence Homology, Amino Acid; D013045:Species Specificity; D020615:Stenotrophomonas maltophilia / Q000187:drug effects / Q000201:enzymology* / Q000235:genetics / Q000302:isolation & purification; D001618:beta-Lactamases / Q000096:biosynthesis* / Q000737:chemistry / Q000235:genetics
chemical_list: D000900:Anti-Bacterial Agents; D015378:Imipenem; D001618:beta-Lactamases