Distribution of the number of mutations among <i>mucA</i>, <i>lasR</i> and <i>mexZ</i> genes in hypermutator and nonmutator isolates.

<p>The number of mutations occurring in <i>mucA</i> (blue bars), <i>lasR</i> (green bars) and <i>mexZ</i> (red bars) is expressed as a percentage respect to the total number of mutations found in hypermutator and nonmutator isolates. Above the bars, the total number of mutations per isolate for the hypermutator and nonmutator subpopulations is indicated.</p

Mutational spectra of <i>mucA</i>, <i>lasR</i>, <i>mexZ</i> and MRS genes observed in <i>P. aeruginosa</i> isolates obtained from Argentinean CF patients.

<p>Pie charts indicate the observed percentage for each kind of mutation respect to the total number of mutations occurring in (A) <i>mucA</i>, (B) <i>lasR</i>, (C) <i>mexZ</i> and (D) MRS genes. The analyses on MRS genes include mutations observed in <i>mutS</i> and <i>mutL.</i></p

Bacterial strains, plasmids and primers used in this study.

<p>Tc^r, tetracycline resistance; Gm^r, gentamicin resistance.</p

Association between antibiotic resistance and inactivation of <i>mucA</i>, <i>lasR</i> and <i>mexZ.</i>

<p>(A) Differences in antibiotic resistance in the <i>P. aeruginosa</i> isolates harboring mutations in <i>mucA</i> (mucA-) respect to those without mutations in <i>mucA</i> (mucA+). Data is expressed as the percentage of resistant isolates to ceftazidime, ciprofloxacin, imipenem, meropenem and tobramycin in mucA- and mucA+ isolates. (B) The same analysis was carried out in lasR- and lasR+ isolates and (C) mexZ- and mexZ+ isolates. In the three genes, the observed differences were not significant (Fisher's exact test) for any of the tested antibiotics.</p

Genotypic and morphotypic characterization of the 38 <i>P. aeruginosa</i> CF isolates.

a<p>All isolates were genotyped by PFGE using the <i>SpeI</i> enzyme.</p>b<p>Mutation frequency was measured as the occurrence of spontaneous resistance to rifampin 100 µg/ml.</p>c<p>Isolates 15a and 25a with mutation frequencies nearly under the breakpoint (≥2×10⁻⁷) were discarded to be <i>mutS</i> or <i>mutL</i> deficient strains by gene sequencing (see <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0012669#pone-0012669-t002" target="_blank">Table 2</a>).</p><p>SCV, Small Colony Variant; ND, not determined; HNC, Hospital de Niños de Córdoba; HABA, Hospital Alemán de Buenos Aires.</p><p>Those isolates with mutation frequencies ≥2×10⁻⁷ were defined as hypermutators and indicated by bold type.</p><p>Mutation frequencies for PAO1 reference strain and MPAOMS and MPAOML hypermutator strains were (2.4±1.3)×10⁻⁸, (2.8±1.6)×10⁻⁶ and (1.3±0.6)×10⁻⁶ respectively.</p

Antibiotic disk diffusion test and quantification of the resistant mutant subpopulations of the 38 <i>P. aeruginosa</i> CF isolates<b>.</b>

a<p>MRS genes was considered positive (+) when the sequences of <i>mutS</i> and <i>mutL</i> genes were wild type and negative (−) when were mutated.</p><p>DD, diffusion diameter zone; RMS, resistant mutant subpopulation: +<10 mutants; ++ 10 to 100 mutants; +++ >100 mutants.</p><p>Zone diameter interpretative criteria was according to CLSI: S, susceptible; I, intermediate resistance; R, resistant.</p><p>*lack of diffusion zone that prevents the resistant mutant subpopulation to be quantified.</p