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 ؋ 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 secondorder 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.

Stenotrophomonas maltophilia: an Emerging Global Opportunistic Pathogen

“…These strains were proposed to be the result of a mutation of the mutS gene of the mismatch repair system. The data from that study suggested that the cost of hypermutation does not hinder chronic infection of the lung by these hypermutable strains (335). These results are in agreement with those reported for P. aeruginosa isolates obtained from the lungs of CF patients (252).…”

“…NC_011071). Both S. maltophilia genomes (from K279A and R551-3) contain genes for the mismatch repair (MMR) system, the guanine oxidation system, the nucleotide excision system, the recombination repair system, and the SOS system (335). The MMR genes of both isolates shared high sequence identity, ranging from 90 to 95%.…”

“…A closer examination of the MMR genes mutS, mutL, and uvrD in these isolates and their corresponding amino acid sequences revealed polymorphisms in MutS, MutL, and UvrD. Defects of the MutS protein were suggested to result in the emergence of hypermutable strains from patients (335).…”

Whole-Genome Sequence of Stenotrophomonas maltophilia D457, a Clinical Isolate and a Model Strain

“…In addition, S. maltophilia is an increasingly relevant human opportunistic pathogen that is involved in infections at hospitals and in patients with cystic fibrosis (5,21). One of the most worrisome properties of S. maltophilia consists of its low susceptibility to most antibiotics currently in use for the treatment of infections (13).…”

The role of bacterial hypermutation in biofilm formation and antibiotic resistance in urinary tract infections caused by pathogens of the Enterobacteriaceae family

“…We were the first to confirm that the mutation frequency classification developed for E. coli by Baquero et al and applied to Stenotrophomonas [41] can also be extended to other Enterobacteriaceae species isolated from urinary tract infections.…”