serogroup O5 was responsible for the outbreak of gastroenteritis in Czechoslovakia in 1965.

Several authors have attributed the explosive outbreak of gastroenteritis that occurred in Czechoslovakia in 1965 to a toxigenic strain of serogroup O37 based on unverified metadata associated with three particular strains from the American Type Culture Collection. Here, by sequencing the original strain preserved at the Czech National Collection of Type Cultures since 1966, we show that the strain responsible for this outbreak was actually a O5 that lacks the genes encoding the cholera toxin, the toxin-coregulated pilus protein and pathogenicity islands present in O37 strains.