Genotypic and morphotypic characterization of the 38 P. aeruginosa CF isolates.

aAll isolates were genotyped by PFGE using the SpeI enzyme.bMutation frequency was measured as the occurrence of spontaneous resistance to rifampin 100 µg/ml.cIsolates 15a and 25a with mutation frequencies nearly under the breakpoint (≥2×10−7) were discarded to be mutS or mutL deficient strains by gene sequencing (see Table 2).SCV, Small Colony Variant; ND, not determined; HNC, Hospital de Niños de Córdoba; HABA, Hospital Alemán de Buenos Aires.Those isolates with mutation frequencies ≥2×10−7 were defined as hypermutators and indicated by bold type.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.