title: Comparison of O-polysaccharide and hemolysin co-regulated protein as target antigens for serodiagnosis of melioidosis.
abstract: BACKGROUND
  Melioidosis is a severe disease caused by Burkholderia pseudomallei. Clinical manifestations are diverse and acute infections require immediate treatment with effective antibiotics. While culture is the current diagnostic standard, it is time-consuming and has low sensitivity. In endemic areas, inaccessibility to biosafety level 3 facilities and a lack of good serodiagnostic tools can impede diagnosis and disease surveillance. Recent studies have suggested that O-polysaccharide (OPS) and hemolysin co-regulated protein 1 (Hcp1) are promising target antigens for serodiagnosis of melioidosis.
  
  
  RESULTS
  We evaluated rapid ELISAs using crude antigens, purified OPS and Hcp1 to measure antibody levels in three sets of sera: (i) 419 serum samples from melioidosis patients, Thai and U.S. healthy donors, (ii) 120 serum samples from patients with other bacterial infections, and (iii) 423 serum samples from 200 melioidosis patients obtained upon admission and at 12 and 52 weeks post-recovery. We observed significantly higher antibody levels using the crude antigen prepared from wild type B. pseudomallei K96243 compared to that of an OPS-mutant. The areas under receiver operator characteristics (AUROCCs) for diagnosis were compared for individual Hcp1-ELISA or OPS-ELISA or combined Hcp1/OPS-ELISA. For Thai donors, AUROCCs were highest and comparable between the Hcp1-ELISA and the combined Hcp1/OPS-ELISA (0.95 versus 0.94). For U.S. donors, the AUROCC was highest for the combined Hcp1/OPS-ELISA (0.96). Significantly higher seropositivity was observed in diabetic patients compared to those without diabetes for both the Hcp1-ELISA (87.3% versus 69.7%) and OPS-ELISA (88.1% versus 60.6%). Although antibody levels for Hcp1 were highest upon admission, the titers declined by week 52 post-recovery.
  
  
  CONCLUSIONS
  Hcp1 and OPS are promising candidates for serodiagnosis of melioidosis in different groups of patients. The Hcp1-ELISA performed better than the OPS-ELISA in endemic areas, thus, Hcp1 represents a promising target antigen for the development of POC tests for acute melioidosis.
authors.affiliation: Department of Microbiology and Immunology, Faculty of Tropical Medicine, Mahidol University, Bangkok, Thailand.|Department of Clinical Pathology, Faculty of Medicine, Vajira Hospital, Navamindradhiraj University, Bangkok, Thailand.
authors.forename: Apinya
authors.initials: A
authors.lastname: Pumpuang
authors.affiliation: Mahidol-Oxford Tropical Medicine Research Unit, Faculty of Tropical Medicine, Mahidol University, Bangkok, Thailand.|Centre for Tropical Medicine & Global Health, Nuffield Department of Medicine, University of Oxford, Oxford, United Kingdom.
authors.forename: Susanna J
authors.initials: SJ
authors.lastname: Dunachie
authors.affiliation: Department of Microbiology and Immunology, Faculty of Tropical Medicine, Mahidol University, Bangkok, Thailand.
authors.forename: Phornpun
authors.initials: P
authors.lastname: Phokrai
authors.affiliation: Mahidol-Oxford Tropical Medicine Research Unit, Faculty of Tropical Medicine, Mahidol University, Bangkok, Thailand.
authors.forename: Kemajittra
authors.initials: K
authors.lastname: Jenjaroen
authors.affiliation: Department of Microbiology and Immunology, Faculty of Tropical Medicine, Mahidol University, Bangkok, Thailand.
authors.forename: Kitisak
authors.initials: K
authors.lastname: Sintiprungrat
authors.affiliation: Department of Clinical Pathology, Faculty of Medicine, Vajira Hospital, Navamindradhiraj University, Bangkok, Thailand.
authors.forename: Siriphan
authors.initials: S
authors.lastname: Boonsilp
authors.affiliation: Department of Microbiology and Immunology, University of South Alabama, Mobile, Alabama, United States of America.
authors.forename: Paul J
authors.initials: PJ
authors.lastname: Brett
authors.affiliation: Department of Microbiology and Immunology, University of South Alabama, Mobile, Alabama, United States of America.
authors.forename: Mary N
authors.initials: MN
authors.lastname: Burtnick
authors.affiliation: Department of Microbiology and Immunology, Faculty of Tropical Medicine, Mahidol University, Bangkok, Thailand.|Mahidol-Oxford Tropical Medicine Research Unit, Faculty of Tropical Medicine, Mahidol University, Bangkok, Thailand.
authors.forename: Narisara
authors.identifier: http://orcid.org/0000-0003-3906-7379
authors.initials: N
authors.lastname: Chantratita
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000907:Antibodies, Bacterial / Q000097:blood*; D001426:Bacterial Proteins / Q000096:biosynthesis*; D016957:Burkholderia pseudomallei / Q000276:immunology*; D004797:Enzyme-Linked Immunosorbent Assay; D006801:Humans; D008554:Melioidosis / Q000175:diagnosis*; D008875:Middle Aged; D019081:O Antigens / Q000276:immunology*; D012372:ROC Curve; D012698:Serologic Tests / Q000379:methods*; D013785:Thailand; D014481:United States; D037521:Virulence Factors / Q000096:biosynthesis*; D055815:Young Adult
chemical_list: D000907:Antibodies, Bacterial; D001426:Bacterial Proteins; C000617886:Hcp1 protein, Burkholderia pseudomallei; D019081:O Antigens; D037521:Virulence Factors