Association of Vibrio cholerae O1 El Tor and O139 Bengal with the Copepods Acartia tonsa and Eurytemora affinis

Abstract

The association of Vibrio cholerae with zooplankton has been suggested as an important factor in transmission of human epidemic cholera, and the ability to colonize zooplankton surfaces may play a role in the temporal variation and predominance of the two different serogroups (V. cholerae O1 El Tor and O139) in the aquatic environment. To date, interactions between specific serogroups and species of plankton remain poorly understood. Laboratory microcosm experiments were carried out to compare quantitatively the colonization of two copepod species, Acartia tonsa and Eurytemora affinis, by each of the epidemic serogroups. V. cholerae O1 consistently achieved higher abundances than V. cholerae O139 in colonizing adults of each copepod species as well as the multiple life stages of E. affinis. This difference in colonization may be significant in the general predominance of V. cholerae O1 in cholera epidemics in rural Bangladesh where water supplies are taken directly from the environment.Vibrio cholerae O1 El Tor and O139 Bengal are recognized as causative agents of cholera and are responsible for cholera epidemics in India and Bangladesh. More than 10 years ago, V. cholerae O139 Bengal was recognized as a newly emerged epidemic variant when it replaced V. cholerae O1 El Tor for two successive cholera seasons (9). It is not clear what factors contributed to the emergence of serogroup O139 as an epidemic variant or to its present coexistence with serogroup O1, but recent research provides strong evidence that horizontal transfer of genes among environmental strains of V. cholerae was a mechanism of its origin (4,12,15).Since the emergence of V. cholerae O139 in the Gangetic Delta region, both V. cholerae O1 and O139 have continued to cause cholera outbreaks with regular seasonality but with temporal variation in the prevalence of the two serogroups (3, 41). Yearly differences in reported cases of cholera caused by V. cholerae O1 and O139 suggest that differences may exist in resource utilization and responses to changing environmental conditions in the aquatic habitat as well as in the immunity of susceptible human populations. Publications that compare V. cholerae O1 and O139 emphasize molecular distinctions (15,16,34,36) and environmental distribution (1,30,43). No studies have explored the mechanisms by which the genotypes of V. cholerae may differ in their resource use. However, Simidu et al. (44) showed that different phenotypes of vibrios aggregated in different microhabitats, suggesting that temporal and spatial variation in the environment play important roles in the relative abundance of phenotypes.

Bacteria dispersal by hitchhiking on zooplankton

“…The importance of zooplankton as carrier has been shown for pathogenic bacteria, most notably Vibrio spp. (26). However, the significance of zooplankton association goes beyond pathogenic bacteria, because zooplankton harbors very diverse bacterial phylotypes (19) in great abundances.…”

Environmental signatures associated with cholera epidemics

“…These regional differences strongly indicate an important effect of the local environment and local zooplankton populations on the dynamics of cholera epidemics. Indeed for Kolkata, higher values of CHL ano reflected the more intense algal blooms than normal that occurred and led to larger zooplankton populations that were comprised mainly of crustacean copepods, a natural aquatic host for V. cholerae (1,8,9). From the analyses of the Dhaka, Bangladesh data, it was concluded that the tidal intrusion of coastal water carrying plankton into inland water could initiate increased human contact with the cholera vibrio (14), because water used for daily hygiene, personal consumption, and religious rites (e.g., ablu- tions) in rural areas of Bangladesh and India is taken directly from local rivers or ponds essentially untreated (13,23,24).…”

“…V. cholerae can be found attached to the carapace and in the gut of copepods in large numbers, the copepod essentially serving as a vector for this human pathogen (1,8,9). A single copepod, for example, can contain as many as 10 3 -10 5 V. cholerae cells (10).…”

Engineering Microbial Physiology with Synthetic Polymers: Cationic Polymers Induce Biofilm Formation inVibrio choleraeand Downregulate the Expression of Virulence Genes

“…In aquatic environments, V. cholerae persists by forming biofilms on the surfaces of phytoplankton, zooplankton and chitin debris. 19,20 Biofilms offer a protective environment both against aquatic predators or in the host environment. Overall, the ability to switch between motile and biofilm lifestyles, along with the carefully controlled induction of virulence factors, is central to the establishment of disease and the emergence of cholera epidemics.…”