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Cross-Reaction Between Vibrio mimicus N-57 and V. cholerae O139 Bengal

Of 200 V. mimicus isolates screened, only one — N-57, recovered from pond water — agglutinated with O139 polyclonal antiserum absorbed only with a rough V. cholerae strain, and did NOT react with the fully absorbed O139 diagnostic antiserum (absorbed with V. cholerae O22 and O155 as well) V. mimicus N-57 cross-reacts with V. cholerae O139

Antigenic Relationship and Structural Basis

Cross-absorption showed an a,b-a,c relationship: O139 and N-57 share epitope 'a' but each has unique epitopes. N-57 also cross-reacted with V. cholerae O22 and Aeromonas trota but not O155. Structural work on a related V. mimicus strain N-1990 confirmed a shared galactosyl residue with a 4,6-cyclic phosphate as the structural basis for cross-reactivity Shared 4,6-cyclophosphate galactose explains cross-reactivity

Diagnostic and Virulence Findings

N-57 was negative on O139-specific MAbs (ICL11, ICL12), the Bengal SMART rapid test, and O139-specific PCR (no 416 bp amplicon). It lacked the ctx gene and produced neither cholera toxin-like nor heat-stable enterotoxin, suggesting it would not cause watery diarrhoea. Antiserum to N-57 completely protected 4-day-old infant mice against 100 LD50 of O139 strain AI-1852 (LD50 = 10³ CFU/0.1 mL), while pre-immune serum afforded no protection — implying the shared epitope is protective Cross-protection in infant mouse model and toxin profile

Critical Assessment

Strengths: Systematic screening of 200 isolates with multiple complementary methods (agglutination, absorption, LPS SDS-PAGE/immunoblot, PCR, toxin assays, mouse challenge) strengthens the serological relationship claim. Limitations: Only ONE cross-reactive isolate was identified among 200; the prevalence of O139 cross-reactivity within V. mimicus is therefore low and uncertain. The infant mouse protection used passive transfer of polyclonal antiserum at a single dilution (1:10) without dose-response or epitope-specific controls. Structural polysaccharide and rfb gene studies on N-57 specifically were NOT completed — structural inference relies on the separate N-1990 study. Geographic sampling is limited to Bangladesh-region water sources. The authors' speculation about O139 rfb gene donors and vaccine strain potential remains untested Authors flag incomplete structural/genetic characterisation of N-57

Related Context

V. mimicus and V. cholerae share a common serogrouping scheme and are closely related species differentiated robustly by multilocus enzyme electrophoresis MEE differentiates V. mimicus from V. cholerae

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Study Novelty

First report of a V. mimicus strain assigned to a new serogroup O194 cross-reacting with O139 Bengal, expanding the known O139 cross-reactive bacterial landscape and informing the hunt for the rfb gene donor.

Scientific Quality

Systematic multi-method serological characterisation with an in vivo protection model is solid; however, single-isolate prevalence, one-dilution protection assay, lack of dose-response, and incomplete N-57 structural/genetic work limit strength. No reported conflicts of interest.

Study Generality

Specific to V. mimicus-O139 antigenic cross-reactivity but broadly informs serogroup evolution, O-antigen epitope sharing, and diagnostic specificity across pathogenic vibrios.

Study Usefulness

Directly relevant to cholera diagnostic specificity (ruling out misdiagnosis by MAbs/SMART/PCR) and to identifying O139 rfb gene donors and vaccine strain candidates.

Study Reproducibility

Standardised serological, LPS-SDS-PAGE, PCR, and animal protocols described with strain designations; however, raw agglutinin titres are partially illegible in the extracted table and no sequence data are deposited.

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