I have been reading a fantastic paper by Murase et al (2022): "Genomic dissection of the Vibrio cholerae O-serogroup global reference strains: reassessing our view of diversity and plasticity between two chromosomes".
There are about 200 O-serogroups of V. cholerae known, but only serogroups O1 and O139 are found in the current pandemic lineage (7PET lineage). Non-O1, non-O139 serogroups of V. cholerae are relatively poorly studied, but can also contribute to much smaller outbreaks of milder diarrhoeal illness (e.g. by serogroup O75, and by serogroup O37).
Sequencing of serogroup reference strains
In this paper, Murase et al have sequenced and analysed the whole set of V. cholerae O-serogroup reference strains. This included 210 O-serogroups that have been identified, taking the Sakazaki collection, which included 194 V. cholerae strains, 14 V. mimicus strains and 2 V. metoecus strains. Among the reference strains, three strains were identified as Aeromonas sp. and one as V. fluvialis, so these were excluded from further analyses and they just focussed on the remaining 206 strains (including 190 V. cholerae).
O-antigen biosynthetic clusters
Murase et al found that there were 9 strain pairs that had almost identical O-antigen biosynthetic gene clusters, and were also serologically identical. They removed these from the accredited O-antigen reference list (removing the underlined serogroup): O5 and O185, O17 and O198, O18 and O136, O20 and O121, O31 and O84, O68 and O129, O74 and O200, O85 and O163, and O87 and O119.
Interestingly, Murase et al also found that there were 16 pairs of strains with almost identical O-antigen biosynthetic gene clusters on chromosome 1, but different serological patterns. They suggest this is likely due to presence of additional O-antigen biosynthesis genes in those strains at secondary loci on chromosome 2.
Pathogenwatch
I have added a "collection" to Pathogenwatch for the Murase et al paper, containing 190 V. cholerae genomes, which you can see here.
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