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

Emerging Strategies against Non-Typhoidal Salmonella: From Pathogenesis to Treatment

Even with the intensive efforts by public health programs to control and prevent it, non-typhoidal Salmonella (NTS) infection remains an important public health challenge. It is responsible for approximately 150 million illnesses and 60,000 deaths worldwide annually. NTS infection poses significant risks with high rates of morbidity and mortality, leading to potential short- and long-term complications. There is growing concern among health authorities about the increasing incidence of antimicrobial resistance, with multidrug resistance totaling 22.6% in Europe, highlighting an urgent need for new therapeutic approaches. Our review aims to provide a comprehensive overview of NTS infection. We outline the molecular mechanisms involved in the pathogenesis of NTS infection, as well as the events leading to invasive NTS infection and the subsequent complications associated with it. Given the widespread implications of antimicrobial resistance, our review also presents the global landscape of resistance, including multidrug resistance, and delve into the underlying mechanisms driving this resistance. The rising rates of antibiotic resistance frequently lead to treatment failures, emphasizing the importance of investigating alternative therapeutic options. Therefore, in this review we also explore potential alternative therapies that could offer promising approaches to treating NTS infections.

Rapid stool antigenic test for typhoid fever among suspected cases, Northeast, Ethiopia

Typhoid fever continued to be the key cause of morbidity and mortality in developing countries with poor hygienic practices and limited access to safe drinking water. The Widal card agglutination test is the main diagnostic tool in Ethiopia, which is limited in differentiating the overlapping symptoms with other acute febrile illnesses such as malaria and viral enteritis. This eventually leds to unnecessary antibiotic use and eventual drug resistance. Therefore this study wants to assess the burden and associated potential risk factors of typhoid fever among suspected cases using the typhoid rapid stool antigen test in Northeast Ethiopia. A hospital-based cross-sectional study was conducted at Gaint and Meket Shediho primary hospitals from May to July 2021. A total of 255 patients clinically suspected of typhoid fever, and willing to grant informed consent were included systematically. The demographic and hygiene-related variables were collected using a pre-tested structured questionnaire. The rapid stool antigenic test and xylose-lysine-deoxycholate agar (XLD) stool culture were evaluated for the level of agreement. The present study indicated that the prevalence of typhoid fever was 15.3%. This displayed that the human-restricted infectious disease, typhoid fever remained a challenge to Ethiopians. Washing hands with soap, history of typhoid fever, having previous history of hospitalization, and chronic underlying disease was the significant potential factor for typhoid fever. The higher agreement of the rapid stool antigenic test with the stool culture can indicate the factual burden of typhoid fever in the suspected population. This could minimize empiric treatment and the possible emergence of drug resistance. Thus, resource-poor settings may need to look for a rapid and reliable stool antigenic test.

Point-of-care diagnosis of invasive non-typhoidal Salmonella enterica in bloodstream infections using immunomagnetic capture and loop-mediated isothermal amplification

Invasive non-typhoidal salmonellosis is gaining worldwide attention as an emerging disease cluster among bloodstream infections. The disease has the highest burden among immunocompromised and malnourished children in resource-limited areas due to poor access to reliable and rapid diagnostics. Point-of-care (POC) diagnostics are promising for use in such low infrastructure laboratory settings. However, there still remains a major challenge for POC testing to deal with the complexity of blood matrices in rapid detection of an extremely low concentration of blood-borne pathogens. In this work, the challenges were addressed by combining magnetic bead based pathogen concentration and Loop Mediated Isothermal Amplification (LAMP) technology. Sensitivity and performance of the combined approach were determined and compared with a direct PCR method. A direct visual detection strategy, adapted using SYTO-24 DNA intercalating dye, resulted in a limit of detection (LoD) as low as 14 CFU/mL in blood samples with a total analysis time of less than 2 h, including sample preparation. This approach has the potential for wide application as a high-throughput POC testing method to analyze pathogens in clinical, food, feed and environmental samples.

Leapfrogging laboratories: the promise and pitfalls of high-tech solutions for antimicrobial resistance surveillance in low-income settings

The scope and trajectory of today’s escalating antimicrobial resistance (AMR) crisis is inadequately captured by existing surveillance systems, particularly those of lower income settings. AMR surveillance systems typically collate data from routine culture and susceptibility testing performed in diagnostic bacteriology laboratories to support healthcare. Limited access to high quality culture and susceptibility testing results in the dearth of AMR surveillance data, typical of many parts of the world where the infectious disease burden and antimicrobial need are high. Culture and susceptibility testing by traditional techniques is also slow, which limits its value in infection management. Here, we outline hurdles to effective resistance surveillance in many low-income settings and encourage an open attitude towards new and evolving technologies that, if adopted, could close resistance surveillance gaps. Emerging advancements in point-of-care testing, laboratory detection of resistance through or without culture, and in data handling, have the potential to generate resistance data from previously unrepresented locales while simultaneously supporting healthcare. Among them are microfluidic, nucleic acid amplification technology and next-generation sequencing approaches. Other low tech or as yet unidentified innovations could also rapidly accelerate AMR surveillance. Parallel advances in data handling further promise to significantly improve AMR surveillance, and new frameworks that can capture, collate and use alternate data formats may need to be developed. We outline the promise and limitations of such technologies, their potential to leapfrog surveillance over currently available, conventional technologies in use today and early steps that health systems could take towards preparing to adopt them.

Performance of molecular methods for the detection of Salmonella in human stool specimens

Background: The relationship between asymptomatic Salmonella exposure within the gastrointestinal tract and Salmonella bacteraemia is poorly understood, in part due to the low sensitivity of stool culture and the lack of validated molecular diagnostic tests for the detection of Salmonella in the stool. The study aimed to determine a reliable molecular diagnostic test for Salmonella in stool specimens.

Methods: We optimised an in-house monoplex real-time polymerase chain reaction (PCR) for the detection of Salmonellattr and InvA genes in stool by including a selenite broth pre-culture step for Salmonella before DNA extraction and validated their specificity against other local common pathogens. Then we assessed their performance against a well-validated multiplex PCR targeting the same ttr and InvA genes and against stool culture using clinical stool specimens collected from a cohort of 50 asymptomatic healthy Malawian children that were sampled at 1-month intervals over 12 months. We employed a latent Markov model to estimate the specificities and sensitivities of PCR methods.

Results: Ttr and InvA primers were both able to detect all the different Salmonella serovars tested and had superior limits of detection when DNA was extracted after selenite pre-culture. T tr sensitivity and specificity for monoplex-PCR were (99.53%, 95.46%) and for multiplex-PCR (90.30%, 99.30%) respectively. InvA specificity and specificity for using monoplex-PCR was (95.06%, 90.31%) and multiplex-PCRs (89.41%, 98.00%) respectively. Sensitivity and specificity for standard stool culture were 62.88% and 99.99%, respectively. Culture showed the highest PPV (99.73%), and monoplex- ttr had the highest NPV (99.67%).

Conclusion: Test methods demonstrated high concordance, although stool culture and monoplexed ttr primers had superior specificity and sensitivity, respectively. The use of selenite pre-enrichment step increased Salmonella detection rate. Taken together, molecular detection methods used here could be used to reveal the true extent of both asymptomatic and symptomatic Salmonella exposure events.

Performance of molecular methods for the detection of Salmonella in human stool specimens

Background: The relationship between asymptomatic Salmonella exposure within the gastrointestinal tract and Salmonella bacteraemia is poorly understood, in part due to the low sensitivity of stool culture, and the lack of validated molecular diagnostic tests for the detection of Salmonella in stool. The study aimed to determine a reliable molecular diagnostic test for Salmonella in stool specimens. Methods: We optimized an in-house monoplex real time polymerase chain reaction (PCR) for the detection of Salmonella TTR and InvA genes in stool by including a selenite broth pre-culture step for Salmonella before DNA extraction, and validated their specificity against other local common pathogens. Then we assessed their performance  against a well-validated multiplex PCR targeting the same TTR and InvA genes, and against stool culture using clinical stool specimens collected from a cohort of 50 asymptomatic healthy Malawian children that were sampled at 1-month intervals over a period of 12 months. We employed a latent Markov model to estimate the specificities and sensitivities of PCR methods. Results: TTR and InvA primers were both able to detect all the different Salmonella serovars tested, and had superior limits of detection if DNA was extracted after selenite pre-culture. TTR sensitivity and specificity for monoplex-PCR were (99.53%, 95.46%) and for multiplex-PCR (90.30%, 99.30%) respectively. InvA specificity and specificity for using monoplex-PCR was (95.06%, 90.31%) and multiplex-PCRs (89.41%, 98.00%) respectively. Sensitivity and specificity for standard stool culture were 62.88% and 99.99% respectively. Culture showed the highest PPV (99.73%) and mono-TTR had the highest NPV (99.67%). Conclusion: Test methods demonstrated high concordance although stool culture and monoplexed TTR primers had superior specificity and sensitivity respectively. The use of selenite pre-enrichment step increased Salmonella detection rate. Taken together, molecular detection methods used here could be used to reveal the true extent of both asymptomatic and symptomatic Salmonella exposure events.

Causes of fever in primary care in Southeast Asia and the performance of C-reactive protein in discriminating bacterial from viral pathogens

OBJECTIVES

This study investigated causes of fever in the primary levels of care in Southeast Asia, and evaluated whether C-reactive protein (CRP) could distinguish bacterial from viral pathogens.

METHODS

Blood and nasopharyngeal swab specimens were taken from children and adults with fever (>37.5 °C) or history of fever (<14 days) in Thailand and Myanmar.

RESULTS

Of 773 patients with at least one blood or nasopharyngeal swab specimen collected, 227 (29.4%) had a target organism detected. Influenza virus type A was detected in 85/227 cases (37.5%), followed by dengue virus (30 cases, 13.2%), respiratory syncytial virus (24 cases, 10.6%) and Leptospira spp. (nine cases, 4.0%). Clinical outcomes were similar between patients with a bacterial or a viral organism, regardless of antibiotic prescription. CRP was higher among patients with a bacterial organism compared with those with a viral organism (median 18 mg/L, interquartile range [10-49] versus 10 mg/L [≤8-22], p = 0.003), with an area under the curve of 0.65 (95% CI 0.55-0.75).

CONCLUSIONS

Serious bacterial infections requiring antibiotics are an exception rather than the rule in the first line of care. CRP testing could assist in ruling out such cases in settings where diagnostic uncertainty is high and routine antibiotic prescription is common. The original CRP randomised controlled trial was registered with ClinicalTrials.gov, number NCT02758821.

Best Practices of Blood Cultures in Low- and Middle-Income Countries

Bloodstream infections (BSI) have a substantial impact on morbidity and mortality worldwide. Despite scarcity of data from many low- and middle-income countries (LMICs), there is increasing awareness of the importance of BSI in these countries. For example, it is estimated that the global mortality of non-typhoidal Salmonella bloodstream infection in children under 5 already exceeds that of malaria. Reliable and accurate diagnosis of these infections is therefore of utmost importance. Blood cultures are the reference method for diagnosis of BSI. LMICs face many challenges when implementing blood cultures, due to financial, logistical, and infrastructure-related constraints. This review aims to provide an overview of the state-of-the-art of sampling and processing of blood cultures, with emphasis on its use in LMICs. Laboratory processing of blood cultures is relatively straightforward and can be done without the need for expensive and complicated equipment. Automates for incubation and growth monitoring have become the standard in high-income countries (HICs), but they are still too expensive and not sufficiently robust for imminent implementation in most LMICs. Therefore, this review focuses on "manual" methods of blood culture, not involving automated equipment. In manual blood cultures, a bottle consisting of a broth medium supporting bacterial growth is incubated in a normal incubator and inspected daily for signs of growth. The collection of blood for blood culture is a crucial step in the process, as the sensitivity of blood cultures depends on the volume sampled; furthermore, contamination of the blood culture (accidental inoculation of environmental and skin bacteria) can be avoided by appropriate antisepsis. In this review, we give recommendations regarding appropriate blood culture sampling and processing in LMICs. We present feasible methods to detect and speed up growth and discuss some challenges in implementing blood cultures in LMICs, such as the biosafety aspects, supply chain and waste management.

Salmonella Typhi, Paratyphi A, Enteritidis and Typhimurium core proteomes reveal differentially expressed proteins linked to the cell surface and pathogenicity

Background

Salmonella enterica subsp. enterica contains more than 2,600 serovars of which four are of major medical relevance for humans. While the typhoidal serovars (Typhi and Paratyphi A) are human-restricted and cause enteric fever, non-typhoidal Salmonella serovars (Typhimurium and Enteritidis) have a broad host range and predominantly cause gastroenteritis.

Methodology/Principle findings

We compared the core proteomes of Salmonella Typhi, Paratyphi A, Typhimurium and Enteritidis using contemporary proteomics. For each serovar, five clinical isolates (covering different geographical origins) and one reference strain were grown in vitro to the exponential phase. Levels of orthologous proteins quantified in all four serovars and within the typhoidal and non-typhoidal groups were compared and subjected to gene ontology term enrichment and inferred regulatory interactions. Differential expression of the core proteomes of the typhoidal serovars appears mainly related to cell surface components and, for the non-typhoidal serovars, to pathogenicity.

Conclusions/Significance

Our comparative proteome analysis indicated differences in the expression of surface proteins between Salmonella Typhi and Paratyphi A, and in pathogenesis-related proteins between Salmonella Typhimurium and Enteritidis. Our findings may guide future development of novel diagnostics and vaccines, as well as understanding of disease progression.

With an estimated 20 million typhoid cases and an even higher number of non-typhoid cases the health burden caused by salmonellosis is huge. Salmonellosis is caused by the bacterial species Salmonella enterica and over 2500 different serovars exist, of which four are of major medical relevance for humans: Typhi and Paratyphi A cause typhoid fever while Typhimurium and Enteritidis are the dominant cause of non-typhoidal Salmonella infections. The proteome is the entire set of proteins that is expressed by a genome and the core proteome are all orthologous proteins detected in a given sample set. In this study we have investigated differential expression of the core proteomes of the Salmonella serovars Typhi, Paratyphi A, Typhimurium and Enteritidis, as well as the regulating molecules. Our comparative proteome analysis indicated differences in the expression of surface proteins between the serovars Typhi and Paratyphi A, and in pathogenesis-related proteins between Typhimurium and Enteritidis. Our findings in proteome-wide expression may guide the development of novel diagnostics and vaccines for Salmonella, as well as understanding of disease.

Typhoid Fever Diagnosis in Endemic Countries: A Clog in the Wheel of Progress?

Typhoid fever causes significant morbidity and mortality in developing countries, with inaccurate estimates in some countries affected, especially those situated in Sub-Saharan Africa. Disease burden assessment is limited by lack of a high degree of sensitivity and specificity by many current rapid diagnostic tests. Some of the new technologies, such as PCR and proteomics, may also be useful but are difficult for low-resource settings to apply as point-of-care diagnostics. Weak laboratory surveillance systems may also contribute to the spread of multidrug resistant Salmonella serovar Typhi across endemic areas. In addition, most typhoid-endemic countries employ serological tests that have low sensitivity and specificity making diagnosis unreliable. Here we review currently available typhoid fever diagnostics, and advances in serodiagnosis of S. Typhi.