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Chan SH, Liau SH, Low YJ, Chng KR, Wu Y, Chan JSH, Tan LK. A Real-Time PCR Approach for Rapid Detection of Viable Salmonella Enteritidis in Shell Eggs. Microorganisms 2023; 11:microorganisms11040844. [PMID: 37110268 PMCID: PMC10143610 DOI: 10.3390/microorganisms11040844] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/04/2023] [Revised: 03/14/2023] [Accepted: 03/17/2023] [Indexed: 03/29/2023] Open
Abstract
Rapid and robust detection assays for Salmonella Enteritidis (SE) in shell eggs are essential to enable a quick testing turnaround time (TAT) at the earliest checkpoint and to ensure effective food safety control. Real-time polymerase chain reaction (qPCR) assays provide a workaround for the protracted lead times associated with conventional Salmonella diagnostic testing. However, DNA-based analysis cannot reliably discriminate between signals from viable and dead bacteria. We developed a strategy based on an SE qPCR assay that can be integrated into system testing to accelerate the detection of viable SE in egg-enriched cultures and verify the yielded SE isolates. The specificity of the assay was evaluated against 89 Salmonella strains, and SE was accurately identified in every instance. To define the indicator for a viable bacteria readout, viable or heat-inactivated SE were spiked into shell egg contents to generate post-enriched, artificially contaminated cultures to establish the quantification cycle (Cq) for viable SE. Our study has demonstrated that this technique could potentially be applied to accurately identify viable SE during the screening stage of naturally contaminated shell eggs following enrichment to provide an early alert, and that it consistently identified the serotypes of SE isolates in a shorter time than conventional testing.
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Affiliation(s)
- Siew Herng Chan
- National Centre for Food Science, Singapore Food Agency, 7 International Business Park, Singapore 609919, Singapore
| | - Sock Hwee Liau
- National Centre for Food Science, Singapore Food Agency, 7 International Business Park, Singapore 609919, Singapore
| | - Ying Jia Low
- National Centre for Food Science, Singapore Food Agency, 7 International Business Park, Singapore 609919, Singapore
| | - Kern Rei Chng
- National Centre for Food Science, Singapore Food Agency, 7 International Business Park, Singapore 609919, Singapore
| | - Yuansheng Wu
- National Centre for Food Science, Singapore Food Agency, 7 International Business Park, Singapore 609919, Singapore
| | - Joanne Sheot Harn Chan
- National Centre for Food Science, Singapore Food Agency, 7 International Business Park, Singapore 609919, Singapore
- Department of Food Science and Technology, National University of Singapore, S14 Level 5 Science Drive 2, Singapore 117542, Singapore
| | - Li Kiang Tan
- National Centre for Food Science, Singapore Food Agency, 7 International Business Park, Singapore 609919, Singapore
- Correspondence: ; Tel.: +65-6019-5826
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Teh CSJ, Lau MY, Chong CW, Ngoi ST, Chua KH, Lee WS, Thong KL. One-step differential detection of Salmonella enterica serovar Typhi, serovar Paratyphi A and other Salmonella spp. by using a quadruplex real-time PCR assay. J Microbiol Methods 2021; 183:106184. [PMID: 33662480 DOI: 10.1016/j.mimet.2021.106184] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/25/2020] [Revised: 02/24/2021] [Accepted: 02/26/2021] [Indexed: 12/14/2022]
Abstract
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.
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Affiliation(s)
- Cindy Shuan Ju Teh
- Department of Medical Microbiology, Faculty of Medicine, University of Malaya, 50603 Kuala Lumpur, Malaysia.
| | - Min Yi Lau
- Department of Medical Microbiology, Faculty of Medicine, University of Malaya, 50603 Kuala Lumpur, Malaysia
| | - Chun Wie Chong
- School of Pharmacy, Monash University Malaysia, 47500 Bandar Sunway, Selangor, Malaysia
| | - Soo Tein Ngoi
- Department of Medical Microbiology, Faculty of Medicine, University of Malaya, 50603 Kuala Lumpur, Malaysia
| | - Kek Heng Chua
- Department of Biomedical Science, Faculty of Medicine, University of Malaya, 50603 Kuala Lumpur, Malaysia
| | - Way Seah Lee
- Department of Paediatrics, Faculty of Medicine, University of Malaya, 50603 Kuala Lumpur, Malaysia
| | - Kwai Lin Thong
- Nanotechnology & Catalysis Research Centre, Deputy Vice Chancellor (Research & Innovation), University of Malaya, 50603 Kuala Lumpur, Malaysia
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