A Study of Antigenic Variation in Vibrio cholerae

Abstract

SUMMARY: The variations in Vibrio cholerae studied included changes from Ogawa to Inaba type, smooth+rough, and motile-+non-motile. With a sloppy-agar technique it was possible to estimate the rate of formation of thcse variants (i.e. probable mutation rate 1 in 1 0 5 and 1 in lo4, respectively). It was possible to show that the action of antiserum in promoting the change from Ogawa to Inaba was selective rather than mutagenic. With the other two variations studied no selective process had to be considered owing to their high spontaneous rate of appearance. It may be said that all three variations studied were due to spontaneous mutants in the parent cultures giving rise to these forms.The studies of Gardner & Venkatraman (1935) showed that vibrio species could be separated on the basis of their somatic '0' antigens, while the flagellar 'H' antigens were widely shared. Since then the differentiation of Vibrio cholerae, the pathogen of cholera, from similar cholera-like vibrios, rests on its agglutinability with specific '0 ' antisera. V . cholerae constituted 0 group I, in this scheme of classification, along with certain haemolytic 'El Tor' vibrios. The definition of V. cholerae as a non-haemolytic vibrio belonging to 0 group I (Gardner & Venkatraman) is now generally accepted, and 0 antisera prepared with heat-killed suspensions are almost universally used for the identification of V . cholerae, in the absence of any reliable biochemical critera. Gardner & Venkatraman (1935) also confirmed the observations of early Japanese workers (Kabeshima, 1918; Nobechi, 1923) when they defined subtypes Inaba, Ogawa and Hikojima in V. cholerae which, while sharing group-specific 0 antigens, differed in minor type-specific 0 antigens. Types Inaba and Ogawa were the 'end' types, usually designated by the antigenic symbols AC and AB respectively, while Hikojima formed the intermediate type ARC. I n view of the poor content of antigen C in Hikojima strains, as well as its presence in Ogawa type cultures when grown a t ZOO, Kauffmann (1950) suggested that Ogawa-Hikojima types constituted one form of V . cholerae, as distinct from the Inaba form.Cholera outbreaks in India are usually confined to a single type of Vibrio cholerae in localized areas, though the type may vary from place to place and epidemic to epidemic. Hikojima-type strains seem to be of rare occurrence while Inaba and Ogawa types have contributed to most epidemic outbreaks. The shift between these two types, over several years, in the cholera endemic

Multidrug-resistant Vibrio cholerae O1 in Belgaum, south India

“…V. cholerae O1 strains are known to interconvert between the Ogawa and Inaba forms (Colwell et al, 1995;Garg et al, 2000) and the wbeT gene of the highly conserved wbe region is responsible for the serotype conversion (Garg et al, 2000). The frequency of conversion of Ogawa to Inaba is approximately 10 25 (Bhaskaran & Gorrill, 1957), whereas conversion from Inaba to Ogawa is much rarer and may be dependent on the strain (Manning et al, 1994). Isolation of both Ogawa and Inaba serotypes during this outbreak is suggestive of the same phenomenon.…”

Mutations in the rfbT Gene Are Responsible for the Ogawa to Inaba Serotype Conversion in Vibrio cholerae O1

“…The phenomenon of sero-conversion has been reported by many investigators (2,4,14,20,23). Although the mechanism of the serotype conversion had not been well understood, comparison of the rfbT genes derived from various Ogawa and Inaba strains suggested that the serotype conversion might be caused by genetic alterations of the rfbT gene.…”

“…These serotypes, however, are not stable. Conversion of serotypes is known to occur during subculture in vitro, passage in vivo, or even during a pandemic (2,14,20,23). The mechanism of this spontaneous serotype conversion has not been well understood yet.…”

Serotype cycles in cholera dynamics

“…Complementary approaches include statistical modelling of cholera dynamics based on this serotype model, along with stronger surveillance programs and more comprehensive re-challenge studies. The extreme sensitivity to the cross-immunity parameter also some of the variability in immunity cycle lengths of the stochastic model (figure 3), and therefore why trends in serotype dominance may seem irregular or not readily apparent (Bhaskaran & Gorrill 1957;ProMed Digest 2005).…”

“…However, the reason for these fluctuations has not been understood, and the identification of regularities of these patterns is absent (Bhaskaran & Gorrill 1957;ProMed Digest 2005). A long-term cholera dataset provided by the International Centre for Diarrheal Disease Research, Bangladesh allows for the quantitative study of the origin of these serotype patterns (figure 1a).…”