Community investigation of Escherichia coli, and Shigella species in freshwater environment of Sirajganj district, Bangladesh

Background/Question/Methods: In recent years the first sing of globally increasing levels of water pollution have been confirmed. Certain virotypes of Escherichia coli, and Shigella spp. are two most important waterborne pathogens. Although E. coli, and Shigella spp. are similar in many ways, recovery of environmental Shigella spp. by the conventional cultural means still remains a challenge. In this investigation denaturant gradient gel electrophoresis (DGGE) analysis of polymerase chain reaction (PCR) amplified deoxyribonucleic acid (DNA) fragments were used to identify a stable community of E. coli, and Shigella spp. in the freshwater environment of Sirajganj district in the Bangladesh. Sampling was made during August 2011 to January 2012.

Results/Conclusions: The phyla e.g. Actinobacteria, Gammaproteobacteria, Firmicutes, Betaproteobacteria, Deltaproteobacteria, Cyanobacteria, and Bacteroidetes were found as the representatives of freshwater bacterial groups whose identities were established by the excising and sequencing DGGE bands and comparing the 16S rDNA sequences with those available in GenBank. Relatively the number of Deltaproteobacteria, Cyanobacteriaig, and Actinobacteria was very low. The phyla Betaproteobacteria, Firmicutes, and Bacteroidetes were present with Gammaproteobacteria in maximum cases. With varying degrees of identity, the Escherichia-Shigella group, Bacillus sp., Verminephrobacter sp., Acidovorax sp., Streptococcus sp., Synechococcus sp., Arthrobacter sp., Shewanella sp., Acinetobacter sp., Flavobacterium sp., Aeromonas sp., Bacteroides sp., Polaromonas sp., Vibrio sp., Staphylococcus sp., Yersinia sp., Pelobacter sp., Alkalilimnicola sp., Pseudomonas sp., and some uncultured bacterial sequences were identified. The Escherichia-Shigella group was present in almost all the representative samples. Significant correlation was found between the four genes ial, virA, ipaBCD, and ipaH specific for Shigella spp., and enteroinvasive E. coli. Betaproteobacteria, Gammaproteobacteria, Firmicutes, and Bacteroidetes were always present with these four genes. There was no such relationship between the E. coli specific genes lt1, stx1, and bfp relative to the presence of the phyla. The total community of E. coli, and Shigella spp. could not be detected due to specific enrichment used in this investigation. The identified community is a reflection of the partial community. This might help recovery of Shigella spp. from environmental samples hither to difficult to isolate culturally.