Abstract
Aeromonads are aquatic bacteria associated with frequent outbreaks of diarrhea in coastal Bangladesh, but their potential risks from environmental sources have remained largely unexplored. This study, over 2 years, examined homestead pond waters in the region for monthly dynamics and diversity of Aeromonas spp. The bacterial counts showed bi-modal annual growth peak, pre- and post-monsoon, strongly correlating (p < 0.0005) with temperature. Of 200 isolates characterized, Aeromonas veronii bv. sobria (27%) was predominant among co-existent Aeromonas schubertii (20%), Aeromonas hydrophila (17%), Aeromonas caviae (13%), and three more. PCR screening of virulence-related genes identified 15 genotypes (I to XV), however, enterotoxigenicity in animal model was observed for five genotypes, ca. 18% (nine of 50) strains, prevalent in A. veronii bv. sobria, A. hydrophila, and A. caviae. Pathogenic strains were distinguishable by possessing at least three of the major virulence genes: ascV, hlyA, ela, ast, and alt, together with accessory virulence factors. PFGE of XbaI-digested genomic DNA revealed high genetic diversity and distant lineage of potentially toxigenic clones. Therefore, along with increased global warming, Aeromonas spp. having multi-factorial virulence potential in coastal ponds that serve as drinking water sources pose a potential health risk, and underscores the need for routine monitoring.
Highlights
The coastal region along the Bay of Bengal, Bangladesh is considered to be one of the most vulnerable areas of the world where climate change mediated impacts are imminent [1]
Results of the present study show that A. veronii bv. sobria, A. hydrophila, and A. caviae, which are the dominant species among the Aeromonas populations in coastal homestead ponds in Bangladesh, are potentially enterotoxigenic
The present study shows that the pathogenic potential of Aeromonas strains in causing diarrhea greatly depends on a combined presence of the major virulence genes: ascV, ast, and/or hlyA, and alt, along with cooccurrence of accessory virulence-stimulatory genes, ela, act, and aerA
Summary
The coastal region along the Bay of Bengal, Bangladesh is considered to be one of the most vulnerable areas of the world where climate change mediated impacts are imminent [1]. Saline intrusion into the shallow aquifers of this region is a serious problem for millions of rural residents who are vulnerable to waterborne diseases since the ponds serve as their source of water for household purposes, including drinking [2]. Aeromonads are among the aquatic bacteria associated with water and food-borne diseases in tropical regions [3]. These aquatic bacteria are implicated as causative agents of a variety of disease conditions in aquatic animals, Toxigenic Aeromonads in Coastal Pond including economically important prawns and fishes. In the central inland areas of Bangladesh, Aeromonas spp. have been reported to be associated with gastroenteritis, with a yearly isolation rate between 9 and 16% of stool samples collected from patients with diarrhea [4]. There is a lack of information regarding the seasonal abundance, diversity of pathogenic potential, and the molecular traits of Aeromonas spp. in the coastal region of the Bengal delta
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