Antimicrobial resistance and genetic characteristics of integron-carrier shigellae isolated in Hungary (1998–2008)

Antimicrobial susceptibility, integron carriage, genetic relationship and presence of some important virulence genes of the integron-carrier strains of Shigella sonnei (n = 230) and Shigella flexneri (n = 22) isolated from stool samples of patients in Hungary between 1998 and 2008 were investigated. Sixty-seven per cent (168/252) of the strains were resistant to sulfamethoxazole/trimethoprim (SxT) followed by streptomycin (S, 47 %), ampicillin (A, 32 %) and tetracycline (Tc, 28 %). Thirty-six per cent (90/252) exhibited multidrug resistance, mostly showing SSxTTc or ASSxTc, ASSxTTc resistance patterns. An S. sonnei strain of imported origin was resistant to cefotaxime and harboured a bla_CTX-M-55-type extended-spectrum β-lactamase gene. Altogether 33 % of the S. sonnei (n = 75) and 14 % of the S. flexneri (n = 3) strains had either class 1 or class 2 integrons or both. The variable regions encoded aadA1 or dfrA1-aadA1 genes for the class 1 and dfrA1-sat2-aadA1 or dfrA1-sat2 genes for the class 2 integrons. Pulsed-field gel electrophoresis analysis revealed that those strains that have different integron types represented different genetic clusters. The Shiga toxin (stx1) gene was identified in one S. sonnei strain and the cdtB gene was detected in an S. flexneri strain. The results reveal the high incidence of antibiotic resistance among Shigella isolates and the presence of the stx1 gene in S. sonnei and the cdtB gene in S. flexneri. The genetic diversity of Shigella spp. isolated recently in Hungary was also demonstrated.