Suppressed Induction of Proinflammatory Cytokines by a Unique Metabolite Produced by Vibrio cholerae O1 El Tor Biotype in Cultured Host Cells

Abstract

Vibrio cholerae O1 has two biotypes, El Tor and Classical, and the latter is now presumed to be extinct in nature. Under carbohydrate-rich growth conditions, El Tor biotype strains produce the neutral fermentation end product 2,3-butanediol (2,3-BD), which prevents accumulation of organic acids from mixed acid fermentation and thus avoids a lethal decrease in the medium pH, while the Classical biotype strains fail to do the same. In this study, we investigated the inhibitory effect of 2,3-BD on the production of two proinflammatory biomarkers, intreleukin-8 (IL-8) and tumor necrosis factor alpha (TNF-␣), in human intestinal epithelial HT29 and alveolar epithelial A549 cells. Cell-free culture supernatants of El Tor strain N16961 grown in LB supplemented with 1% glucose induced a negligible amount of IL-8 or TNF-␣, while the Classical O395 strain induced much higher levels of these proinflammatory cytokines. On the other hand, three mutant strains constructed from the N16961 strain with defects in the constitutive 2,3-BD pathway were also able to induce high levels of cytokines. When HT29 and A549 cells were treated with bacterial flagella, known proinflammatory cytokine inducers, and chemically synthesized 2,3-BD at various concentrations, a dose-dependent decrease in IL-8 and TNF-␣ production was observed, demonstrating the suppressive effect of 2,3-BD on the production of proinflammatory cytokines in epithelial cells. Upon cotreatment with extraneous 2,3-BD, elevated levels of IB␣, the inhibitor of the NF-B pathway, were detected in both HT29 and A549 cells. Furthermore, treatments containing 2,3-BD elicited lower levels of NF-B-responsive luciferase activity, demonstrating that the reduced cytokine production is likely through the inhibition of the NF-B pathway. These results reveal a novel and potential role of 2,3-BD as an immune modulator that might have conferred a superior pathogenic potential of the El Tor over the Classical biotype.Cholera, an acute watery diarrheal disease, is caused by toxigenic strains of the enteric pathogen Vibrio cholerae and is mainly associated with consumption of contaminated water (39). On the basis of O-antigen typing, V. cholerae has more than 200 identified serogroups, among which only O1 and O139 are reported to be toxigenic. Seven recent pandemics of cholera have been caused by O1 serogroup strains, although O139 strains were reported to be associated with Asiatic cholera epidemics (7, 24, 37). The O1 serogroup of V. cholerae has further been classified into two biotypes, El Tor and Classical. Among the seven worldwide historical pandemics, the Classical strains are presumed to be the etiologic agent for the first six but are only presumed to be the etiologic agent due to the lack of ample epidemiologic surveillance, while the El Tor strains emerged as the major cause during the ongoing seventh pandemic. The reasons behind the extinction of the Classical biotype and the emergence of the El Tor biotype remain unclear, although several hypotheses have been proposed. The tw...

Interspecific bacterial sensing through airborne signals modulates locomotion and drug resistance

“…It is becoming clear that VOCs have a role in interkingdom interactions between bacteria and eukaryotic cells. For example, Vibrio cholerae O1 produces the gaseous compound 2,3-butanediol, which interacts with the human immune system by suppressing the induction of immune modulators 17 . Bacterial VOCs also have been shown to promote plant growth 18 and induce systemic resistance in Arabidopsis 19 .…”

Selective and Efficient Elimination of Vibrio cholerae with a Chemical Modulator that Targets Glucose Metabolism

“…Host cell culture was performed as described previously (Bari et al, 2011). Intestinal epithelial HT29 cells (ATCC, Rockville, MD, USA) were cultured in Dulbecco's Modified Eagle Medium (DMEM) supplemented with 10% FBS (WelGENE, Korea), 2.5 mM L-glutamine, 100 U/mL penicillin, and 100 μg/mL streptomycin at 37°C in a 5% CO 2 atmosphere in a water-jacketed incubator (Forma Scientific, USA).…”

“…Further, it is proposed that the production of acetoin may account for the greater evolutionary fitness of V. cholerae El Tor biotype compared to the classical biotype (Yoon and Mekalanos, 2006). Additionally, acetoin production offers V. cholerae cells a survival advantage during infection by down regulating the host innate immune responses (Bari et al, 2011). These findings support the hypothesis that inhibiting acetoin production could provide a novel antibacterial mechanism for V. cholerae elimination.…”

Immunomodulation for gastrointestinal infections

“…Products of bacterial metabolism can contribute to immunomodulation of the host response by V. cholerae , where the product of glucose metabolism, 2,3-butanediol, modulates the activation of host response by suppressing the secretion of IL-8 and TNF-α in an NF-κB dependent fashion on intestinal ECs [82]. The metabolite is specific for V. cholerae El Tor strains, which have been shown a competitive advantage over V. cholerae classical strains [83].…”