An unusual cluster of dysentery due to Shigella dysenteriae type 4 in Dhaka, Bangladesh

Genetic structure of the nadA and nadB antivirulence loci in Shigella spp

Comparison of nadA and nadB in 14 Shigella strains and enteroinvasive Escherichia coli versus E. coli showed that at least one locus is altered in all strains. These observations explain the characteristic nicotinic acid auxotrophy of Shigella organisms and are consistent with the previously identified antivirulence nature of these genes for these pathogens.

The emerging strains of Shigella dysenteriae type 2 in Bangladesh are clonal

A total of 113 strains of Shigella dysenteriae type 2 isolated from patients attending the Dhaka diarrhoea treatment centre of ICDDR,B: Centre for Health and Population Research during the period 1999-2004 were studied. Serotype of the isolates was confirmed using commercially available antisera. Except for arabinose fermentation, all the strains had similar biochemical reactions. More than 60% of the strains were sensitive to commonly used antibiotics; only 6% (n=7) of the strains were resistant to nalidixic acid, and none of the strains were resistant to mecillinam and ciprofloxacin. All strains were invasive as demonstrated by the presence of a 140 MDa plasmid, ial, sen and ipaH genes, Congo Red absorption ability and by the Sereny test performed on representative strains. Plasmid patterns were heterogeneous but more than 50% of strains were confined to a single pattern. All strains possessed a 1.6 MDa plasmid and 87% of the strains contained a 4 MDa plasmid. Middle-range plasmids (90 MDa to 30 MDa) present in 36% of the strains were not associated with antibiotic resistance. All the strains were clustered within a single type with four subtypes by pulsed-field gel electrophoresis while ribotyping patterns of all the strains were identical.