Simultaneous and high sensitive detection of Salmonella typhi and Salmonella paratyphi a in human clinical blood samples using an affordable and portable device

Rapid and specific differentiation of Salmonella enterica serotypes typhi and Paratyphi by multicolor melting curve analysis

Rapid and accurate identification of Salmonella enterica serotypes Typhi and Paratyphi (A, B and C), the causal agents of enteric fever, is critical for timely treatment, case management and evaluation of health policies in low and middle-income countries where the disease still remains a serious public health problem. The present study describes the development of a multiplex assay (EFMAtyping) for simultaneous identification of pathogens causing typhoid and paratyphoid fever in a single reaction by the MeltArray approach, which could be finished within 2.5 h. Seven specific genes were chosen for differentiation of typhoidal and nontyphoidal Salmonella. All gene targets were able to be detected by the EFMAtyping assay, with expected Tm values and without cross-reactivity to other relevant Salmonella serovars. The limit of detection (LOD) for all gene targets was 50 copies per reaction. The LOD reached 102-103 CFU/ml for each pathogen in simulated clinical samples. The largest standard deviation value for mean Tm was below 0.5 °C. This newly developed EFMAtyping assay was further evaluated by testing 551 clinical Salmonella isolates, corroborated in parallel by the traditional Salmonella identification workflow, and serotype prediction was enabled by whole-genome sequencing. Compared to the traditional method, our results exhibited 100% of specificity and greater than 96% of sensitivity with a kappa correlation ranging from 0.96 to 1.00. Thus, the EFMAtyping assay provides a rapid, high throughput, and promising tool for public health laboratories to monitor typhoid and paratyphoid fever.

Low-Cost Arduino Reverse Transcriptase Loop-Mediated Isothermal Amplification (RT-LAMP) for Sensitive Nucleic Acid Detection

This work presents a low-cost transcription loop-mediated isothermal amplification (RT-LAMP) instrument for nucleic acid detection, employing an Arduino Nano microcontroller. The cooling system includes customized printed circuit boards (PCBs) that serve as electrical resistors and incorporate fans. An aluminum block is designed to accommodate eight vials. The system also includes two PCB heaters-one for sample heating and the other for vial lid heating to prevent condensation. The color detection system comprises a TCS3200 color 8-sensor array coupled to one side of the aluminum heater body and a white 8-LED array coupled to the other side, controlled by two Multiplexer/Demultiplexer devices. LED light passes through the sample, reaching the color sensor and conveying color information crucial for detection. The top board is maintained at 110 ± 2 °C, while the bottom board is held at 65 ± 0.5 °C throughout the RT-LAMP assay. Validation tests successfully demonstrated the efficacy of the colorimetric RT-LAMP reactions using SARS-CoV-2 RNA amplification as a sample viability test, achieving 100% sensitivity and 97.3% specificity with 66 clinical samples. Our instrument offers a cost-effective (USD 100) solution with automated result interpretation and superior sensitivity compared to visual inspection. While the prototype was tested with SARS-CoV-2 RNA samples, its versatility extends to detecting other pathogens using alternative primers, showcasing its potential for broader applications in biosensing.

One-step differential detection of Salmonella enterica serovar Typhi, serovar Paratyphi A and other Salmonella spp. by using a quadruplex real-time PCR assay

Diseases caused by typhoidal and non-typhoidal Salmonella remain a considerable threat to both developed and developing countries. Based on the clinical symptoms and serological tests, it is sometimes difficult to differentiate the Salmonella enterica serovar Paratyphi A (S. enterica serovar Paratyphi A) from serovar Typhi (S. enterica serovar Typhi). In this study, we developed a quadruplex real-time polymerase chain reaction (PCR) assay with an internal amplification control (IAC), to simultaneously differentiate S. enterica serovar Paratyphi A from serovar Typhi and to detect other Salmonella serovars which cause salmonellosis in humans. This assay was evaluated on 155 salmonellae and non-salmonellae strains and demonstrated 100% specificity in species differentiation. Inclusion of an IAC did not affect the efficiency of the assay. Further evaluation using a blind test on spiked stool, blood and food specimens showed that the detection limit was at 10³ -10⁴ CFU/mL (or g) and a high PCR efficiency with different targets (R² > 0.99), except for S. enterica serovar Paratyphi A in blood. This assay has been applied to clinical specimens to detect the causative agents of gastrointestinal infections and has successfully identified 6 salmonellosis patients from the 50 diarrhoea patients. The quadruplex real-time PCR developed in this study could enhance the detection and differentiation of salmonellae. This assay could be applied to stools, blood and food based on the notable performance in the simulation tests and field evaluation.