title: Polymorphic mutation frequencies of clinical and environmental Stenotrophomonas maltophilia populations.
abstract: Mutation frequencies were studied in 174 Stenotrophomonas maltophilia isolates from clinical and nonclinical environments by detecting spontaneous rifampin-resistant mutants in otherwise-susceptible populations. The distribution of mutation frequencies followed a pattern similar to that found for other bacterial species, with a modal value of 1 x 10(-8). Nevertheless, the proportion of isolates showing mutation frequencies below the modal value (hypomutators) was significantly higher for S. maltophilia than those so far reported in other organisms. Low mutation frequencies were particularly frequent among environmental S. maltophilia strains (58.3%), whereas strong mutators were found only among isolates with a clinical origin. These results indicate that clinical environments might select bacterial populations with high mutation frequencies, likely by second-order selection processes. In several of the strong-mutator isolates, functional-complementation assays with a wild-type allele of the mutS gene demonstrated that the mutator phenotype was due to the impairment of MutS activity. In silico analysis of the amino acid changes present in the MutS proteins of these hypermutator strains in comparison with the normomutator isolates suggests that the cause of the defect in MutS might be a H683P amino acid change.
authors.affiliation: Servicio de Microbiología, Hospital Universitario Ramón y Cajal and Unidad Asociada al CSIC Resistencia a los Antibióticos y Virulencia Bacteriana, Madrid, Spain.
authors.forename: María Carmen
authors.initials: MC
authors.lastname: Turrientes
authors.forename: María Rosario
authors.initials: MR
authors.lastname: Baquero
authors.forename: María Blanca
authors.initials: MB
authors.lastname: Sánchez
authors.forename: Sylvia
authors.initials: S
authors.lastname: Valdezate
authors.forename: Esther
authors.initials: E
authors.lastname: Escudero
authors.forename: Gabrielle
authors.initials: G
authors.lastname: Berg
authors.forename: Rafael
authors.initials: R
authors.lastname: Cantón
authors.forename: Fernando
authors.initials: F
authors.lastname: Baquero
authors.forename: Juan Carlos
authors.initials: JC
authors.lastname: Galán
authors.forename: José Luis
authors.initials: JL
authors.lastname: Martínez
mesh_terms: D000900:Anti-Bacterial Agents / Q000494:pharmacology; D001426:Bacterial Proteins / Q000235:genetics; D024881:Drug Resistance, Bacterial; D004783:Environmental Microbiology; D005816:Genetic Complementation Test; D016905:Gram-Negative Bacterial Infections / Q000382:microbiology*; D051719:MutS DNA Mismatch-Binding Protein / Q000235:genetics; D009154:Mutation; D011110:Polymorphism, Genetic; D012293:Rifampin / Q000494:pharmacology; D020615:Stenotrophomonas maltophilia / Q000235:genetics* / Q000302:isolation & purification
chemical_list: D000900:Anti-Bacterial Agents; D001426:Bacterial Proteins; D051719:MutS DNA Mismatch-Binding Protein; D012293:Rifampin