Hypermutable Pseudomonas aeruginosa in Cystic Fibrosis Patients from Two Brazilian Cities

Abstract

d Hypermutable (HPM) strains of Pseudomonas aeruginosa have been found at high frequencies in cystic fibrosis (CF) patients in Europe. We report the results of testing for HPM frequencies, mutator genotype, and antimicrobial resistance of P. aeruginosa strains from Brazilian CF patients. A modified disk diffusion technique was used to quantify antibiotic-resistant subpopulations of an isolate, and estimations of the frequency of mutation to rifampin resistance were determined for 705 isolates from 149 patients attending clinics in two Brazilian cities. Mutations in the mutS gene were detected by sequencing assays. We found 194 (27.5%) HPM isolates in samples from 99 (66.4%) patients. Thirty-five HPM isolates (18.0%) from 31 (31.3%) patients exhibited a high increased spontaneous mutation rate compared with controls, and eight isolates from six patients displayed a defective mutS gene. The dominant HPM population was associated with very low antibiotic resistance levels, while HPM subpopulations were generally more resistant to antimicrobials. A relatively high prevalence of HPM P. aeruginosa in CF patients was associated with surprisingly low antibiotic resistance levels, in contrast to some earlier studies. Pseudomonas aeruginosa is commonly associated with the chronic, progressive lung disease that is the leading cause of morbidity and mortality in cystic fibrosis (CF) patients (1). During the course of infection, isolates of P. aeruginosa undergo a series of profound genotypic and phenotypic changes to adapt to the CF lung environment, and they promote their survival by maximizing diversity in cell populations. Hypermutation (HPM) in specific regions of the genome is one of the mechanisms used for this purpose and may confer fitness benefits for colonization of anatomical niches (2). It has been shown that 37% to 54% of CF patients chronically infected with P. aeruginosa harbor isolates with a hypermutator phenotype, as defined by an increased spontaneous frequency of mutations (3-5). HPM strains usually exhibit alterations in genes participating in DNA error avoidance systems (6), and the majority of these strains from CF patients are deficient in the mismatch repair system (MRS), with the mutS gene being most frequently affected (3, 4, 7). The MRS is a major barrier to interspecies recombination events. Removal of this barrier also enhances the frequency of horizontal gene transfer, which is an important mechanism of acquired drug resistance in bacteria (8). Maciá and collaborators (4) proposed that the presence of subpopulations of resistant mutant colonies growing in the zone of inhibition of particular antibiotics could be used as a screening test to detect HPM.An association between high antibiotic resistance rates of P. aeruginosa in CF patients and the presence of a high proportion of HPM strains has been repeatedly documented (3,4,7,9), but there is no consensus as to whether there is a causative link between increased antimicrobial resistance and hypermutability.We report here the results of a surve...

Characterization of Hypermutator Pseudomonas aeruginosa Isolates from Patients with Cystic Fibrosis in Australia

“…The prevalence of P. aeruginosa hypermutators in isolates from patients with CF has been examined across several clinics in Europe (15% to 54%; average, 27%) (4,7,8,10,(26)(27)(28)(29) and the Americas (17% to 42%; average, 29%) (9,30,31). However, the prevalence and genetic diversity of hypermutator isolates obtained from patients with CF in Australia have received much less attention.…”

Agmatine accumulation byPseudomonas aeruginosaclinical isolates confers antibiotic tolerance and dampens host inflammation

“…Many of these examples are mutated in only a small fraction of infections (15), which is consistent with the prevalence of aguA mutations (~5%) among our isolate library. While this recovery rate is not nearly as high as QS-deficient ( lasR ), mucoid ( mucA) or hypermutator ( mutS) phenotypes (12, 54, 55), parallel evolution of agmatine hyperproduction in P. aeruginosa derived from multiple patients suggests positive selection at the aguA locus. Since our isolate library was derived from de-identified sputum samples for which clinical data were not available, it is unclear whether agmatine hyperproduction is associated with the transition to chronicity.…”

Assessing the relative importance of bacterial resistance, persistence and hyper-mutation for antibiotic treatment failure

“…We investigate the relative importance of high-persistence, hyper-mutation and resistance mutations (leading to P, M Lutz et al [70] Martinez-Solano et al [59] Montanari et al [40] Macia et al [63] Ciofu et al [69] Ferroni et al [68] Marvig et al [67] Feliziani et al [66] Waine et al [65] Oliver et al [7] Mena et al [8] Rees et al [64] Macia et al [63] Lopez-Causape et al [62] Montanari et al [40] *Kenna et al [58] Mena et al [8] *Mulet et al [61] *Kenna et al [58] *Mulet et al [61] Gutierrez et al [60] Martinez-Solano et al [59] Oliver et al [7] *Kenna et al [58] % frequency of hyper-mutator genotypes and R subpopulations, respectively)-and all their combinations-over the course and after discontinuation of AB treatment by using a stochastic population model (figure 2; electronic supplementary material, table S1). Our model incorporates pharmacokinetic and pharmacodynamic functions to realistically simulate AB treatment (equation (2.1)) and the distinct effects of ABs on our respective subpopulations.…”