title: Recovery and characterization of environmental variants of Shigella flexneri from surface water in Bangladesh.
abstract: Little is known about the distribution, survival, and transmission of Shigella in environmental surface waters. To gain more insight into the environmental biology of Shigella we isolated five bacterial strains serotyped as Shigella flexneri 2b from a freshwater lake in Bangladesh using a modified nutrient broth supplemented with nucleic acid bases. The biochemical properties of the isolates, including inability to ferment lactose and a negative lysine decarboxylase test, indicated common physiological characteristics with Shigella, but differed significantly from that of standard clinical strains. The isolates possessed the ipaH virulence gene and a megaplasmid, but lacked other Shigella-related virulence marker genes. Genetic fingerprinting and sequence analysis of housekeeping genes confirmed the strains as S. flexneri isolates. An apparent clonal origin of strains recovered with a one-year interval indicates a strong environmental selection pressure on Shigella for persistence in the freshwater environment. The lack of a complete set of virulence genes as well as uncommon biochemical properties suggest that these strains might represent a group of non-invasive and atypical environmental Shigella variants, with the potential for further elucidation of the survival mechanism, diversity, and emergence of virulent Shigella in tropical freshwater environments.
authors.affiliation: Department of Microbiology, University of Dhaka, Dhaka, Bangladesh.
authors.forename: Mohammed Ziaur
authors.initials: MZ
authors.lastname: Rahman
authors.forename: Nafisa
authors.initials: N
authors.lastname: Azmuda
authors.forename: Mohammad Jahangir
authors.initials: MJ
authors.lastname: Hossain
authors.forename: Munawar
authors.initials: M
authors.lastname: Sultana
authors.forename: Sirajul Islam
authors.initials: SI
authors.lastname: Khan
authors.forename: Nils-Kåre
authors.initials: NK
authors.lastname: Birkeland
mesh_terms: D001459:Bangladesh; D004405:Dysentery, Bacillary / Q000382:microbiology; D004783:Environmental Microbiology; D014644:Genetic Variation; D006801:Humans; D060106:Lakes / Q000382:microbiology*; D008969:Molecular Sequence Data; D010802:Phylogeny; D012763:Shigella flexneri / Q000145:classification / Q000235:genetics* / Q000302:isolation & purification* / Q000378:metabolism; D037521:Virulence Factors / Q000235:genetics
chemical_list: D037521:Virulence Factors