Vibrio cholerae Classical Biotype Is Converted to the Viable Non-Culturable State when Cultured with the El Tor Biotype

Abstract

A unique event in bacterial epidemiology was the emergence of the El Tor biotype of Vibrio cholerae O1 and the subsequent rapid displacement of the existing classical biotype as the predominant cause of epidemic cholera. We demonstrate that when the El Tor and classical biotypes were cocultured in standard laboratory medium a precipitous decline in colony forming units (CFU) of the classical biotype occurred in a contact dependent manner. Several lines of evidence including DNA release, microscopy and flow cytometric analysis indicated that the drastic reduction in CFU of the classical biotype in cocultures was not accompanied by lysis, although when the classical biotype was grown individually in monocultures, lysis of the cells occurred concomitant with decrease in CFU starting from late stationary phase. Furthermore, uptake of a membrane potential sensitive dye and protection of genomic DNA from extracellular DNase strongly suggested that the classical biotype cells in cocultures retained viability in spite of loss of culturability. These results suggest that coculturing the classical biotype with the El Tor biotype protects the former from lysis allowing the cells to remain viable in spite of the loss of culturability. The stationary phase sigma factor RpoS may have a role in the loss of culturability of the classical biotype in cocultures. Although competitive exclusion of closely related strains has been reported for several bacterial species, conversion of the target bacterial population to the viable non-culturable state has not been demonstrated previously and may have important implications in the evolution of bacterial strains.

Proteolysis of Virulence Regulator ToxR Is Associated with Entry of Vibrio cholerae into a Dormant State

“…Strain O395, where previous studies regarding termination of virulence had been made, belongs to the classical biotype [ 17 , 18 ]. Strains of the El Tor biotype are the source of the current pandemic of cholera and were recently shown to enter VBNC differentially when compared with classical [ 55 ]. We determined the effect of TPI conditions in the El Tor biotype strain N16961.…”

Characterization of Vibrio cholerae Strains Isolated from the Nigerian Cholera Outbreak in 2010

“…The emerging predominance of biotype El Tor is due to the longer persistence of the bacteria in the environment. The mechanisms of selective advantage are not yet known (22). It is also known that the biotype El Tor is responsible for milder infections, with a lower mortality rate in contrast to the classical biotype (8,21).…”

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

“…One of the long-standing questions in cholera epidemiology is how the El Tor biotype strains came to replace classical biotype strains (Pradhan et al, 2013; Kim et al, 2014). Our work shows that the classical biotype strains cannot conduct acetoin production during glucose fermentation even in LBG medium (Table 1), a phenotype identical to that of the N16961 (p)ppGpp 0 mutant.…”