Salmonella Typhi and Paratyphi A infections in Cambodian children, 2012-2016

Salmonella Bacteremia in Spanish Pediatric Emergency Departments: Uncommon But Not Mild

BACKGROUND

Salmonella spp. is an uncommon microorganism in bloodstream infections among pediatric patients in our setting, although in developing countries it is the most common causative organism in blood cultures.

METHODS

We describe the children presenting to pediatric emergency departments and diagnosed with Salmonella bacteremia (SB) and identify clinical and laboratory predictors of poor outcome (ie, complications, sequelae and death) by bivariate analysis. We performed an observational study and subanalysis of a multicenter prospective registry, including patients <18 years of age with a positive blood culture obtained at any of the 22 participating Spanish pediatric emergency departments between 2011 and 2016. We considered young age, chronic diseases, immunosuppressive treatment and intestinal flora disruption as risk factors for SB.

RESULTS

Of the 55 patients with SB (3.2% of registered bacteremia), 32 (58.2%) had no risk factors for SB, 42 (76.3%) had a normal pediatric assessment triangle and 45 (81.8%) an associated gastrointestinal infection (acute gastroenteritis or enteric fever). Nine (16.4%) had a poor outcome, including 1 death (1.8%). A poor outcome was more common in patients with an abnormal pediatric assessment triangle [odds ratio (OR): 51.6; 95% confidence interval (CI): 9.2-289.5], an altered physical examination (OR: 15.2; 95% CI: 4.4-58.8) and elevated C-reactive protein (OR: 1.01; 95% CI: 1.005-1.03).

CONCLUSIONS

Most SBs were related to a gastrointestinal infection. One in 6 children had a poor outcome; abnormal pediatric assessment triangle on arrival (25% of patients) was the main risk factor identified.

A low-background and wash-free signal amplification F-CRISPR biosensor for sensitive quantitative and visible qualitative detection of Salmonella Typhimurium

In traditional CRISPR-based biosensors, the cleavage-induced signal generation is insufficient because only a signals is generated at a CRISPR-induced cleavage. Herein, we developed an improved CRISPR/Cas12a-based biosensor with an enlarged signal generation which integrated the hybridization chain reaction (HCR) and low-background Förster Resonance Energy Transfer (FRET) signal output mode. The HCR with nucleic acid self-assembly capability was used as a signal carrier to load more signaling molecules. To get the best signal amplification, three different fluorescence signal output modes (fluorescence recovery, FRET and low-background FRET) generated by two fluoresceins, FAM and Cy5, were fully investigated and compared. The results indicated that the low-background FRET signal output mode with the strictest signal generation conditions yielded the highest signal-to-noise ratio (S/N) (19.17) and the most obvious fluorescence color change (from red to yellow). In optimal conditions, the proposed biosensor was successfully applied for Salmonella Typhimurium (S. Typhimurium) detection with 6 h (including 4 h for sample pre-treatment) from the initial target processing to the final detection result. The qualitative sensitivity, reliant on color changes, was 103 CFU/mL. The quantitative sensitivity, calculated by the fluorescence value, were 1.62 × 101 CFU/mL, 3.72 × 102 CFU/mL, and 8.71 × 102 CFU/mL in buffer solution, S. Typhimurium-spiked milk samples, and S.Typhimurium-spiked chicken samples, respectively. The excellent detection performance of the proposed biosensor endowed its great application potential in food and environment safety monitoring.

A CG@MXene nanocomposite-driven E-CRISPR biosensor for the rapid and sensitive detection of Salmonella Typhimurium in food

In this study, we developed a novel electrochemical biosensor based on CRISPR/Cas12a (E-CRISPR) for the rapid and sensitive detection of Salmonella Typhimurium (S. Typhimurium). The CRISPR/Cas12a system was applied to identify S. Typhimurium gene and induce signal changes in electrochemical measurement. The colloidal gold and MXene (CG@MXene) nanocomposites were synthesized and immobilized to improve the performance of the biosensor by decreasing the background noise. The formation process of CG@MXene was well characterized, and experiment conditions were fully optimized. Under the optimal conditions, the proposed E-CRISPR biosensor exhibited excellent sensitivity for S. Typhimurium, with a limit of detection (LOD) of 160 CFU/mL, and great specificity against other common foodborne pathogens. Furthermore, the feasibility of the E-CRISPR biosensor was evaluated by analyzing S. Typhimurium-spiked chicken samples, with a recovery rate ranging from 100.46% to 106.37%. In summary, this research proposed a novel E-CRISPR biosensor from a new perspective to detect S. Typhimurium which can be an alternative approach for bacterial detection in the food supply chain.

Molecular diagnosis of bacterial and viral diarrhoea using multiplex-PCR assays: An observational prospective study among paediatric patients from India

PURPOSE

In developing countries, the aetiology of diarrhoea goes undiagnosed as only microscopy, stool culture or enzyme immunoassay are done to find the causative agent. The present study aims to detect common paediatric viral and bacterial diarrhoea pathogens by microscopy, stool culture for bacteria, and multiplex polymerase chain reaction (mPCR) for bacteria and virus detections.

MATERIALS AND METHODS

Diarrheal stool samples (n ​= ​109) received at the laboratory from paediatric patients aged one month to 18 years were included in the study. They were cultured for common bacterial pathogens and simultaneously subjected to two multiplex PCRs one for the detection of Salmonella spp., Shigella spp., Enteroinvasive E.coli and Enteropathogenic E.coli, another for the detection of adenovirus, astrovirus, rotavirus and norovirus.

RESULTS

Of the 109 samples cultured for bacterial aetiology, 0.9% (1/109) grew Salmonella enterica ser.Typhi and 2% (2/109) Shigella flexneri. By mPCR, 16% of samples (17/109) were positive for Shigella spp., 0.9% (1/109) for Salmonella spp., and 21% (23/109) for rotavirus. One sample (0.9%) had rotavirus and Shigella spp., which indicates mixed aetiology.

CONCLUSIONS

Shigella spp. and rotavirus are the prime causative agents of childhood diarrhoea in our region. The rate of detection of bacterial aetiology by culture was poor. Isolation of pathogens by conventional culture helps to know the species, serotypes and antibiotic susceptibility of the pathogens. Virus isolation is cumbersome, time-consuming, and not available for routine diagnostic use. Therefore, real-time mPCR would be a better choice for early detection of pathogens, thereby ensuring timely diagnosis, treatment, and a reduction in mortality.

A CRISPR/Cas12a-mediated, DNA extraction and amplification-free, highly direct and rapid biosensor for Salmonella Typhimurium

CRISPR/Cas-based biosensors were typically used for nucleic-acid targets detection and complex DNA extraction and amplification procedures were usually inevitable. Here, we report a CRISPR/Cas12a-mediated, DNA extraction and amplification-free, highly direct and rapid biosensor (abbreviated as "CATCHER") for Salmonella Typhimurium (S. Typhimurium) with a simple (3 steps) and fast (∼2 h) sensing workflow. Magnetic nanoparticle immobilized anti-S. Typhimurium antibody was worked as capture probe to capture the target and provide movable reaction interface. Colloidal gold labeled with anti-S. Typhimurium antibody and DNase I was used as detection probe to bridge the input target and output signal. First, in the presence of S. Typhimurium, an immuno-sandwich structure was formed. Second, DNase I in sandwich structure degraded the valid, complete activator DNA to invalid DNA fragments which can't trigger the trans-cleavage activity of Cas12a. Finally, the integrity of reporter DNA was preserved presenting a low fluorescence signal. Conversely, in the absence of S. Typhimurium, strong fluorescence recovery appeared owing to the cutting of reporter by activated Cas12a. Significantly, the proposed "CATCHER" showed satisfactory detection performance for S. Typhimurium with the limit of detection (LOD) of 7.9 × 101 CFU/mL in 0.01 M PBS and 6.31 × 103 CFU/mL in spiked chicken samples, providing a general platform for non-nucleic acid targets.

New Insights on the Early Interaction Between Typhoid and Non-typhoid Salmonella Serovars and the Host Cells

Salmonella enterica is a common source of food and water-borne infections, causing a wide range of clinical ailments in both human and animal hosts. Immunity to Salmonella involves an interplay between different immune responses, which are rapidly initiated to control bacterial burden. However, Salmonella has developed several strategies to evade and modulate the host immune responses. In this sense, the main knowledge about the pathogenicity of this bacterium has been obtained by the study of mouse models with non-typhoidal serovars. However, this knowledge is not representative of all the pathologies caused by non-typhoidal serovars in the human. Here we review the most important features of typhoidal and non-typhoidal serovars and the diseases they cause in the human host, describing the virulence mechanisms used by these pathogens that have been identified in different models of infection.