Since the original serotype Y strain and its SfI convertant 1a strain can agglutinate with grouping sera 3;4, we also tested whether this antigen is detectable in serotype 1 d. The LPS of the new serotype was not recognized by the grouping sera 3;4 Gilteritinib concentration (Panel b, Figure 1C). Additionally, serotype-specific genes, gtrX for phage SfX and gtrI for phage SfI, were detected from these new strains by PCR and sequencing of the PCR products. Figure 1 Construction of a novel serotype, 1 d, of S. VX-765 molecular weight flexneri with serotype-converting bacteriophages SfX and SfI. (A) Illustration of construction road map of S. flexneri 036_1d strain from a serotype Y strain 036, by sequential infection

of phages SfX and SfI. (B) Serological identification of S. flexneri AZD6244 concentration 036_1d as serotype 1 d with agglutination test using monovalent diagnostic sera. The constructed strain S. flexneri 036_1d agglutinated with both of typing sera I and grouping sera7;8. (C) Serological identification of S. flexneri 036_1d by Western-blot assay.

The LPS extracted from the tested strains was separated by SDS-PAGE and hybridized with monovalent grouping sera 7;8 (a) and 3;4 (b), and typing sera I (c), respectively. LPS of serotype X strain 014 and serotype 1a strain 019 were used as positive controls for group specific antigen 7;8 and type specific antigen I. After strain name in brackets is the serotype of the strain. S. flexneri serotype 1 Rucaparib chemical structure has three known subtypes, 1a, 1b and 1c, the agglutination patterns of which are defined by a combination of typing and grouping sera, namely typing sera I and grouping sera 3;4 (Y-5) for 1a, typing sera I and grouping sera 6 for 1b, S. flexneri group antigen specific MASF B and provisional specific monoclonal antibody MASF1c for 1c [17] (Table 1). Since the newly constructed serotype agglutinates with typing sera I, but showed a different serological pattern from all known serotype 1 subtypes (Table 1), we named this

new serotype 1 d. In order to determine whether such serotype-converting events could occur in nature, we randomly selected 24 S. flexneri serotype X strains in our collection, and infected them with serotype-converting phage SfI. All 24 strains tested were successfully converted to serotype 1 d. We have no good explanation why serotype 1a strain 036_1a, constructed from 036 by infection with SfI, could not be further infected by SfX. We randomly selected 17 S. flexneri 1a isolates from our collection for infection by SfX but found that none of them could be infected by SfX. Clearly, the SfI can infect the strains carrying serotype-converting phage SfX, but not vice versa, likely due to phage immunity from modified O-antigen receptors [20]. Interestingly, a recent study reported S. flexneri strains with identical serological characteristics to the novel serotype 1 d created in this study [21]. Four strains were designated as untypeable serotype I: (7;8) among 467 S.