Phenotypic and Molecular Characterization of Potentially New Shigella boydii Serotype in Bangladesh
Objective: Shigella is a major cause of bacillary dysentery among children under 5 years of age, especially in low- and middle-income countries. At Dhaka hospital of icddr,b, every year around 3% of Shigella isolates from patients with diarrhea are identified as Shigella-like organisms (SLOs). These isolates do not react with any of the existing and provisional Shigella antisera. The major aims…
A cluster of six Shigella-like organisms (SLOs) discovered at Dhaka Hospital affiliated with icddr,b exhibit distinctive characteristics that may represent a novel provisional serovar of Shigella boydii. These SLOs were identified in 3% of diarrhea patients at the hospital each year. The researchers employed a range of techniques to analyze the isolates, including biochemical tests, serotyping, antimicrobial susceptibility testing, virulence assays, and comparison of pulsed-field gel electrophoresis (PFGE) patterns with known serotypes of Shigella spp.
The six SLOs shared several key features: they fermented mannitol, displayed invasive properties, produced the ipaH and Shigella enterotoxin 2 proteins, and carried a virulence plasmid approximately 140 MDa in size. Antibiotic susceptibility testing revealed a consistent pattern among the isolates: resistance to ampicillin, tetracycline, and sulfamethoxazole-trimethoprim, but sensitivity to mecillinam, nalidixic acid, and ciprofloxacin.
Interestingly, the plasmid and PFGE profiles of these isolates were identical, setting them apart from all other known Shigella boydii serotypes. To further investigate potential cross-reactivity with existing antisera, researchers developed an antiserum against one of the SLOs. This antiserum successfully agglutinated all six isolates, but did not produce cross-reactivity with reference strains of other Shigella spp. or Escherichia coli.
Based on these findings, the researchers propose that the unique cluster of SLOs may represent a new provisional serovar within the Shigella boydii group. Additional analysis is needed to formally incorporate these findings into the current classification scheme for Shigella.
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