Comparison of xMAP Salmonella Serotyping Assay With Traditional Serotyping and Discordance Resolution by Whole Genome Sequencing.

Yun Luo,Dazhi Jin,Ruiting Lan,Julian Ye,Huanying Wang,Sophie Octavia,Chen Huang,Sherry A Dunbar,Yi-Wei Tang

doi:10.3389/fcimb.2020.00452

Abstract

Salmonella spp. are a major cause of foodborne illness throughout the world. Traditional serotyping by antisera agglutination has been used as a standard identification method for many years but newer nucleic acid-based tests have become available that may provide advantages in workflow and test turnaround time. In this study, we evaluated the Luminex® xMAP® Salmonella Serotyping Assay (SSA), a multiplex nucleic acid test capable of identifying 85% of the most common Salmonella serotypes, in comparison to the traditional serum agglutination test (SAT) on 4 standard strains and 255 isolates from human (224), environmental, and food (31) samples. Of the total of 259 isolates, 256 could be typed by the SSA. Of these, 197 (77.0%) were fully typed and 59 (23.0%) were partially typed. By SAT, 246 of the 259 isolates (95%) were successfully typed. Sixty isolates had discrepant results between SAT and SSA and were resolved using whole genome sequencing (WGS). By SAT, 80.0% (48/60) of the isolates were consistent with WGS while by SSA 91.7% (55/60) were partially consistent with WGS. By serovar, all 30 serovars except one tested were fully or partially typable. The workflow comparison showed that SSA provided advantages over SAT with a hands-on time (HOT) of 3.5 min and total turnaround time (TAT) of 6 h, as compared to 1 h HOT and 2–6 days TAT for SAT. Overall, this study showed that molecular serotyping is promising as a rapid method for Salmonella serotyping with good accuracy for typing most common Salmonella serovars circulating in China.

Highlights

Salmonella enterica is responsible for a variety of clinical manifestations in humans
We tested the application of Serotyping Assay (SSA) to type Salmonella isolates circulating in China, a setting different from where the SSA was developed and initially targeted
We showed that SSA was largely consistent with serum agglutination test (SAT) and inconsistencies were partly attributed to SSA, because SSA called more than one serovar including the serovar by SAT

Summary

Introduction

Salmonella enterica is responsible for a variety of clinical manifestations in humans. The enteric fever inducing typhoidal Salmonella has been an important global public health problem. Salmonella Typhi alone causes 22 million outbreak-associated and sporadic cases of typhoid and ∼200,000 deaths annually worldwide (Crump et al, 2004). Non-typhoidal Salmonella is the most common foodborne pathogen around the world and causes an estimated 93.8 million cases and over 155,000 deaths annually (Kariuki et al, 2015). Since most illnesses caused by S. enterica in healthy individuals are self-limiting and not reported, the actual number of cases of illness is undoubtedly much higher. In resource-limited settings, especially in subSaharan Africa and parts of the Indian and Asian subcontinents, morbidity and mortality is likely much higher than that estimated

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