Role of Shrimp Chitin in the Ecology of Toxigenic Vibrio cholerae and Cholera Transmission

Abstract

Seasonal plankton blooms correlate with occurrence of cholera in Bangladesh, although the mechanism of how dormant Vibrio cholerae, enduring interepidemic period in biofilms and plankton, initiates seasonal cholera is not fully understood. In this study, laboratory microcosms prepared with estuarine Mathbaria water (MW) samples supported active growth of toxigenic V. cholerae O1 up to 7 weeks as opposed to 6 months when microcosms were supplemented with dehydrated shrimp chitin chips (CC) as the single source of nutrient. Bacterial counting and detection of wbe and ctxA genes were done employing culture, direct fluorescent antibody (DFA) assay, and multiplex-polymerase chain reaction methods. In MW microcosm, the aqueous phase became clear as the non-culturable cells settled, whereas the aqueous phase of the MW–CC microcosm became turbid from bacterial growth stimulated by chitin. Bacterial chitin degradation and biofilm formation proceeded from an initial steady state to a gradually declining bacterial culturable count. V. cholerae within the microenvironments of chitin and chitin-associated biofilms remained metabolically active even in a high acidic environment without losing either viability or virulence. It is concluded that the abundance of chitin that occurs during blooms plays an important role in the aquatic life cycle of V. cholerae and, ultimately, in the seasonal transmission of cholera.

Microbial Surface Colonization and Biofilm Development in Marine Environments

“…Chitin is highly insoluble, but its degradation products represent an abundant source of carbon, nitrogen, and metabolic energy for microbial communities. Chitin utilization constitutes a key pathway in global carbon and nitrogen cycling (186,193), and this polymer also provides a surface for vibrios to colonize, particularly under adverse environmental conditions (516)(517)(518)(519)(520).…”

Characterizing the Hexose-6-Phosphate Transport System of Vibrio cholerae, a Utilization System for Carbon and Phosphate Sources

“…They deliver organic and inorganic substrates in concentrations that are up to 4 orders of magnitude greater than those found in particle-free open seawater (for a recent review, see reference 2). Therefore, many plants and animals in the ocean serve as microbial niches for V. cholerae (3)(4)(5)(6). For example, copepods or other crustaceans contain or are covered with chitin, a ␤,1-4-linked polymer of 2-acetamido-2-deoxy-␤-D-glucopyranoside (GlcNAc) n and its deacetylated form, chitosan.…”

Interactions ofVibriospp. with Zooplankton

“…In microcosm experiments, V. cholerae O1 survived for 7 weeks in estuarine water collected from Mathbaria (50). In microcosms supplemented with chitin chips, V. cholerae O1 grew actively for up to 6 months, with the microcosms becoming turbid due to bacterial growth.…”

“…with Zooplankton V. cholerae, the causative agent of cholera, a disease that is still at epidemic proportions in many countries where seasonal outbreaks of cholera occur, is also known to attach to zooplankton. Thus, zooplankton may act as a vector for toxigenic strains, enhancing disease transmission (46,47,48,49,50). Recent studies have focused on the interactions of Vibrio spp.…”