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.
Highlights
It is important that infectious diseases are correctly identified as quickly as possible for the sake of both patient care and public health
Little progress has been made to make culturing simpler and quicker – the process still takes days or even weeks, since typically, one or more days are required for the organism to grow in an initial enrichment broth, another day for a subsequent agar subculture, and at least another day to identify any colonies obtained by biochemical analysis
The bacterial suspension obtained from organisms grown overnight in broth was examined in TUBEX TP
Summary
It is important that infectious diseases are correctly identified as quickly as possible for the sake of both patient care and public health. Either or both of the following investigative approaches are usually adopted: (a) Isolation and identification of the infectious agent in culture media, and (b) Detection of antigens of the infectious agent, or antibodies induced by these antigens, in the serum or other body fluids of the infected patient. Which one of these approaches is more appropriate or efficacious depends on the disease. Little progress has been made to make culturing simpler and quicker – the process still takes days or even weeks, since typically, one or more days are required for the organism to grow in an initial enrichment broth, another day for a subsequent agar subculture, and at least another day to identify any colonies obtained by biochemical analysis
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