Microbiological Culture Simplified Using Anti-O12 Monoclonal Antibody in TUBEX Test to Detect Salmonella Bacteria from Blood Culture Broths of Enteric Fever Patients

Abstract

Definitive diagnosis of infectious diseases, including food poisoning, requires culture and identification of the infectious agent. We described how antibodies could be used to shorten this cumbersome process. Specifically, we employed an anti-Salmonella lipopolysaccharide O12 monoclonal antibody in an epitope-inhibition 10-min test (TUBEX TP) to detect O12+ Salmonella organisms directly from routine blood culture broths. The aim is to obviate the need to subculture the broth and subsequently identify the colonies. Thus, blood from 78 young outpatients suspected of having enteric fever was incubated in an enrichment broth, and after 2 or 4 days, broth samplings were examined by TUBEX TP as well as by conventional agar culture and identification. TUBEX TP was performed before the culture results. Eighteen isolates of S. Typhi (15 after 2 days) and 10 isolates of S. Paratyphi A (4 after 2 days) were obtained by conventional culture. Both these Salmonella serotypes, the main causes of enteric fever, share the O12 antigen. In all instances where either of these organisms was present (cultured), TUBEX TP was positive (score 4 [light blue] – to – score 10 [dark blue]; negative is 0 [pink-colored]) i.e. 100% sensitive. Identification of the specific Salmonella serotype in TUBEX-positive cases was achieved subsequently by conventional slide agglutination using appropriate polyclonal antisera against the various serotypes. Twelve Escherichia coli, 1 Alcaligenes spp. and 1 Enterobacter spp. were isolated. All of these cases, including all the 36 culture-negative broths, were TUBEX-negative i.e. TUBEX TP was 100% specific. In a separate study using known laboratory strains, TUBEX TF, which detects S. Typhi but not S. Paratyphi A via the O9 antigen, was found to efficiently complement TUBEX TP as a differential test. Thus, TUBEX TP and TUBEX TF are useful adjuncts to conventional culture because they can save considerable time (>2 days), costs and manpower.

Diagnostic accuracy of antigen-based immunochromatographic rapid diagnostic tests for the detection of Salmonella in blood culture broth

“…noted that the O12 antibody is less immuno-dominant than O9 (or O2) and that although most typhoid patients produce vast amounts of anti-O12 antibodies, many paratyphoid patients produce little or none at all [ 19 ]. In addition, PCR experiments showed that the median number of copies of target DNA per ml of blood was 39 for Salmonella Paratyphi A compared to 60 for Salmonella Typhi which suggests a lower concentration in blood during infection [ 20 , 21 ].…”

Typhoid epidemiology, diagnostics and the human challenge model

“…These assays have often been limited by a high rate of false positivity and low specificity because of nonspecific binding [71 & ]. Antigen detection in precultured blood/broth improves both sensitivity and specificity of the RDT alone, while reducing the technical input and time required to confirm positive S. Typhi or S. Paratyphi blood culture results [87,88].…”

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“…The accuracy of antibiotic prescription quality indicated that 52.73% was rational therapy, 8. 18% was irrational, 7.27% was without indication, and 31.82% could not be interpreted by the observer [23]. There are two types of benchmarks that can be used for antibiotic evaluation and consumption quantity calculation.…”