Dynamic of Mutational Events in Variable Number Tandem Repeats of Escherichia coli O157:H7

A. V. BUSTAMANTE; A. M. SANSO; SEGURA DO; A. E. PARMA; LUCCHESI P.M. A.

JOURNAL OF BIOMEDICINE AND BIOTECHNOLOGY

HINDAWI PUBLISHING CORPORATION

Lugar: New York; Año: 2013 vol. 2013 p. 1 - 9

1110-7243

VNTRs regions have been successfully used for bacterial subtyping; however, the hypervariability in VNTR loci is problematicwhen trying to predict the relationships among isolates. Since few studies have examined the mutation rate of these markers, ouraim was to estimate mutation rates of VNTRs specific for verotoxigenic E. coli O157:H7.The knowledge of VNTR mutational ratesand the factors affecting them would make MLVA more effective for epidemiological or microbial forensic investigations. For thispurpose, we analyzed nine loci performing parallel, serial passage experiments (PSPEs) on 9 O157:H7 strains. The combined 9PSPE population rates for the 8 mutating loci ranged from 4.4 × 10−05 to 1.8 × 10−03 mutations/generation, and the combined 8-locimutation rate was of 2.5 × 10−03 mutations/generation. Mutations involved complete repeat units, with only one point mutationdetected. A similar proportion between single and multiple repeat changes was detected. Of the 56 repeat mutations, 59% wereinsertions and 41% were deletions, and 72% of the mutation events corresponded to O157-10 locus. For alleles with up to 13 UR, aconstant and low mutation rate was observed; meanwhile longer alleles were associated with higher and variable mutation rates.Our results are useful to interpret data from microevolution and population epidemiology studies and particularly point out thatthe inclusion or not of O157-10 locus or, alternatively, a differential weighting data according to the mutation rates of loci must beevaluated in relation with the objectives of the proposed study.