Loop-mediated isothermal amplification for paratyphoid fever - a proof-of-principle analysis

New Developments in PCR-Based Diagnostics for Bacterial Pathogens Causing Gastrointestinal Infections-A Narrative Mini-Review on Challenges in the Tropics

The application of modern PCR approaches for the diagnosis of bacterial gastrointestinal pathogens is on the rise due to their rapidly available results combined with high sensitivity. While multiple studies describe the ongoing implementation of this technique for routine diagnostic purposes in laboratories in Western industrialized countries, reports on successful and also sustainable respective approaches in resource-poor tropical settings are still scarce. In order to shed light on potential reasons for this marked discrepancy, this narrative review summarizes identified challenges for the application of diagnostic PCR targeting bacterial gastrointestinal pathogens from stool samples in the tropics. The identified and discussed issues comprise the lack of generally accepted definitions for (1) minimum standards regarding sample acquisition, storage and transport time for diagnostic PCR analyses in the tropics, (2) nucleic acid extraction standards allowing an optimum detection of all types of pathogens which may be responsible for gastroenteritis in the tropics, (3) validation standards to ensure comparable quality of applied diagnostic assays, and (4) cut-offs for a reliable discrimination of infection and mere colonization in areas where semi-immunity due to repeated exposition associated with poor hygiene conditions has to be expected. Further implementation research is needed to solve those issues.

Classification of Salmonella enterica of the (Para-)Typhoid Fever Group by Fourier-Transform Infrared (FTIR) Spectroscopy

Typhoidal and para-typhoidal Salmonella are major causes of bacteraemia in resource-limited countries. Diagnostic alternatives to laborious and resource-demanding serotyping are essential. Fourier transform infrared spectroscopy (FTIRS) is a rapidly developing and simple bacterial typing technology. In this study, we assessed the discriminatory power of the FTIRS-based IR Biotyper (Bruker Daltonik GmbH, Bremen, Germany), for the rapid and reliable identification of biochemically confirmed typhoid and paratyphoid fever-associated Salmonella isolates. In total, 359 isolates, comprising 30 S. Typhi, 23 S. Paratyphi A, 23 S. Paratyphi B, and 7 S. Paratyphi C, respectively and other phylogenetically closely related Salmonella serovars belonging to the serogroups O:2, O:4, O:7 and O:9 were tested. The strains were derived from clinical, environmental and food samples collected at different European sites. Applying artificial neural networks, specific automated classifiers were built to discriminate typhoidal serovars from non-typhoidal serovars within each of the four serogroups. The accuracy of the classifiers was 99.9%, 87.0%, 99.5% and 99.0% for Salmonella Typhi, Salmonella Paratyphi A, B and Salmonella Paratyphi C, respectively. The IR Biotyper is a promising tool for fast and reliable detection of typhoidal Salmonella. Hence, IR biotyping may serve as a suitable alternative to conventional approaches for surveillance and diagnostic purposes.

Simple differentiation of Salmonella Typhi, Paratyphi and Choleraesuis from Salmonella species using the eazyplex TyphiTyper LAMP assay

Introduction. Identification of typhoidal Salmonella (TS) serovars and their discrimination from non-typhoidal Salmonella (NTS) is conventionally performed by seroagglutination. This method is labour-intensive, requires technical experience and can be inconclusive in some cases. Molecular assays may be reliable alternative diagnostic tools.

Aim. This study was designed to evaluate the eazyplex TyphiTyper based on loop-mediated isothermal amplification (LAMP) for fast identification of TS and S. Choleraesuis in culture.

Methodology. A total of 121 Salmonella strains and 33 isolates of other Enterobacterales species were tested by the eazyplex TyphiTyper. Simulated and clinical blood cultures (BCs) were used to examine the performance of the assay for diagnosis of systemic infection. Sample preparation took about 5 min and the test running time was 20 min. Amplification was measured by real-time fluorescence detection.

Results. All TS and S. Choleraesuis strains were correctly identified. The most common NTS S. Typhimurium (n=34) and S. Enteritidis (n=15) were detected as Salmonella species without any false positive result for TS targets. Cross-reactions of NTS with TS were only rarely observed. Direct testing of positive BCs gave correct results. Sensitivities and specificities of the assay were as follows: 100 and 99.3 % for S. Typhi, 100 and 98.7 % for S. Paratyphi A, 100 and 97.3 % for S. Paratyphi B, 100 and 100 % for S. Paratyphi C, 100 and 100 % for S. Choleraesuis, and 100 and 100 % for Salmonella species, respectively.

Conclusion. The eazyplex TyphiTyper is very easy to perform and allows the rapid identification of TS and S. Choleraesuis isolates.