A high number of multidrug-resistant and predominant genetically related cluster of Shigella flexneri strains isolated over 34 years in Brazil

Shigella flexneri has been a major public health problem in developing countries. This work analyzed the frequency of 16 virulence genes, the genotypic diversity, and the antimicrobial resistance profiles of 130 S. flexneri strains isolated in Brazil. The ipaH gene was found in all the 130 strains. The frequencies of the other genes were variable ial (88.5%), sigA (82.3%), iuc (74.6%), virA (73%), pic (72.3%), virF (57.7%), sat (48.5%), ipaBCD (37%), sen (36%), set1A (35.4%), sepA (30%), set1B (30%), virB (14%), icsA (10%), and ipgD (5.4%). A total of 57 (43.8%) strains were multidrug-resistant. ERIC-PCR grouped 96 of the strains into a single cluster with ≥ 70.4% of similarity, 75 of these strains presented a similarity ≥ 80.9%. PFGE grouped 120 of the strains into a single cluster with 57.4% of similarity and 82 of these strains presented a similarity ≥ 70.6%. In conclusion, the high frequency of some virulence genes reinforces the pathogenic potential of the strains studied. The high rates of MDR strains are alarming once it may lead to failure when antimicrobial treatment is necessary. Genotype techniques reveled a major cluster with high genetic similarity including S. flexneri strains from the different Brazilian states and distinct years of isolation, showing that they probably emerged from a common ancestor.