Genetic relatedness of ciprofloxacin-resistant Shigella dysenteriae type 1 strains isolated in south Asia

Abstract

<I>Objectives</I>: The aim of the present study was to determine the clonal relationships of ciprofloxacin-resistant <I>Shigella dysenteriae</I> type 1 strains isolated from south Asia, and <I>S. dysenteriae</I> 1 strains associated with epidemics in 1978, 1984 and 1994. <I>Methods</I>: The antimicrobial susceptibilities were examined by NCCLS methods. Molecular epidemiological characterization was performed by plasmid profiling, pulsed-field gel electrophoresis (PFGE) and mutation analysis of the quinolone resistance-determining region (QRDR) of <I>gyrA</I> by sequencing. <I>Results</I>: Plasmid patterns of the current ciprofloxacin-resistant strains from India, Nepal and Bangladesh were very similar to those of the 1978, 1984 and 1994 epidemic isolates of <I>S. dysenteriae</I> 1, except for the presence of a new plasmid of ∼2.6 MDa, which was found in one recent ciprofloxacin-resistant strain isolated in Bangladesh. PFGE analysis showed that the ciprofloxacin-resistant strains isolated in Bangladesh, India and Nepal belonged to a PFGE type (type A), which was possibly related to that of the 1984 and 1994 clone of <I>S. dysenteriae</I> 1, but different from 1978 epidemic strains. The current ciprofloxacin-resistant strains belong to five subtypes (A3-A7), all of which were found in India, but in Bangladesh and Nepal, only A3 existed. Mutation analysis of the QRDR of <I>gyrA</I> revealed that amino acid substitutions at positions 83 and 87 of ciprofloxacin-resistant strains isolated in Bangladesh were similar to those of the strains isolated in Nepal, but different (at position 87) from ciprofloxacin-resistant strains isolated in India. <I>Conclusions</I>: PFGE and mutation analysis of <I>gyrA</I> showed differences between the current ciprofloxacin-resistant <I>S. dysenteriae</I> 1 strains isolated in south Asia and those associated with epidemics in 1978, 1984 and 1994.