Classification of a Proteus penneri clinical isolate with a unique O-antigen structure to a new Proteus serogroup, O80

•We proved the serological uniqueness of Proteus penneri Br114 O-antigen.•We have established the chemical structure of P. penneri Br114 O-polysaccharide.•We have created a new Proteus O80 serogroup including the studied strain.•O80 is the fourth Proteus serogroup based on clinical isolates from Łódź, Poland.•Our results confirm the serological heterogeneity of Proteus spp. bacteria.

Proteus penneri is an opportunistic pathogen, which may cause severe diseases, most frequently urinary tract infections in immunocompromised patients. P. penneri Br 114 exhibiting a good swarming growth ability as an S-form strain was isolated from a wound of a patient in Łódź, Poland. Serological studies using ELISA and Western blotting and chemical analyses along with 1H and 13C NMR spectroscopy showed that the O-antigen (O-polysaccharide) of this strain is unique among the known Proteus serotypes O1–O79. It possesses a linear pentasaccharide repeating unit containing a partially O-acetylated amide of d-glucuronic acid (GlcA) with l-serine having the following structure:These data are a basis for creating a new Proteus serogroup, O80, so far represented by the single Br 114 isolate. The O80 is the 21st O-serogroup containing P. penneri strains and the fourth serogroup based on Proteus spp. clinical isolates from Łódź, Poland.

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