title: The TUBEX test detects not only typhoid-specific antibodies but also soluble antigens and whole bacteria.
abstract: TUBEX (IDL Biotech) is a 5 min semiquantitative colorimetric test for typhoid fever, a widely endemic disease. TUBEX detects anti-Salmonella O9 antibodies from a patient's serum by the ability of these antibodies to inhibit the binding between an indicator antibody-bound particle and a magnetic antigen-bound particle. Herein, we report that TUBEX could also be used to specifically detect soluble O9 lipopolysaccharide in antigen-spiked buffer by the ability of the antigen to inhibit the same binding between the particles. Sensitivity of antigen detection was improved (8-31 mug ml(-1)) by using a modified protocol in which the test sample was mixed with the indicator particles first, rather than with the magnetic particles as for antibody detection. The antigen was also detectable in spiked serum and urine samples, albeit less well (2-4-fold) than in buffer generally. However, no antigen was detected from six typhoid sera examined, all of which had anti-O9 antibodies. In addition, whole organisms of Salmonella Typhi (15 strains) and Salmonella Enteritidis (6 strains) (both O9(+) Salmonella), grown in simulated blood broths or on MacConkey agar, were also detectable by TUBEX when suspended at >9 x 10(8) organisms ml(-1). Expectedly, Salmonella Paratyphi A (7 strains), Salmonella Typhimurium (1 strain) and Escherichia coli (2 strains) were negative in the test. Thus, the same TUBEX kit may be used in several ways both serologically and microbiologically for the rapid diagnosis of typhoid fever. However, validation of the newer applications will require the systematic examination of real patient and laboratory materials.
authors.affiliation: Clinical Immunology Unit, The Chinese University of Hong Kong, Prince of Wales Hospital, Shatin, New Territories, Hong Kong.
authors.forename: Frankie C H
authors.initials: FCH
authors.lastname: Tam
authors.affiliation: Department of Microbiology, The Chinese University of Hong Kong, Prince of Wales Hospital, Shatin, New Territories, Hong Kong.
authors.forename: Thomas K W
authors.initials: TKW
authors.lastname: Ling
authors.affiliation: Department of Microbiology, The Chinese University of Hong Kong, Prince of Wales Hospital, Shatin, New Territories, Hong Kong.
authors.forename: Kam Tak
authors.initials: KT
authors.lastname: Wong
authors.affiliation: Clinical Immunology Unit, The Chinese University of Hong Kong, Prince of Wales Hospital, Shatin, New Territories, Hong Kong.
authors.forename: Danny T M
authors.initials: DTM
authors.lastname: Leung
authors.affiliation: Department of Microbiology, The Chinese University of Hong Kong, Prince of Wales Hospital, Shatin, New Territories, Hong Kong.
authors.forename: Raphael C Y
authors.initials: RCY
authors.lastname: Chan
authors.affiliation: Clinical Immunology Unit, The Chinese University of Hong Kong, Prince of Wales Hospital, Shatin, New Territories, Hong Kong.
authors.forename: Pak Leong
authors.initials: PL
authors.lastname: Lim
mesh_terms: D000907:Antibodies, Bacterial / Q000097:blood*; D000918:Antibody Specificity; D006801:Humans; D008070:Lipopolysaccharides / Q000032:analysis* / Q000097:blood / Q000276:immunology / Q000652:urine; D019081:O Antigens / Q000032:analysis* / Q000097:blood / Q000276:immunology / Q000652:urine; D011933:Reagent Kits, Diagnostic; D012477:Salmonella enteritidis / Q000276:immunology / Q000302:isolation & purification; D012485:Salmonella typhi / Q000276:immunology* / Q000302:isolation & purification*; D012680:Sensitivity and Specificity; D014435:Typhoid Fever / Q000175:diagnosis / Q000382:microbiology; D014556:Urine / Q000382:microbiology
chemical_list: D000907:Antibodies, Bacterial; D008070:Lipopolysaccharides; D019081:O Antigens; D011933:Reagent Kits, Diagnostic