SINGAPORE – Researchers from the National Center for Food Science of the Singapore Food Agency and the National University of Singapore have created a real-time polymerase chain reaction (PCR) method for the detection of viable Salmonella Enteritidis contamination in shell eggs that, if integrated, would speed up the current Salmonella testing procedure.

When verifying the identity of S. enteritidis isolates obtained from naturally contaminated eggs, the researchers claim that the assay is similar to the “gold standard”.

Shell eggs are a frequent source of infection for S. enteritidis, one of the serovars that cause foodborne salmonellosis most frequently worldwide.

Even though checking for viable S. enteritidis in shell eggs is crucial for early warnings and making sure that contaminated food does not reach the market, the traditional “gold standard” culture-based testing methods demand numerous time-consuming stages and employees with specialized technical expertise.

It typically takes five to seven days for a culture-based system that used live isolates to confirm the presence of S. enteritidis.

However, there have been reports of false-positive Salmonella results from biochemical testing of colony isolates from bacteria other than Salmonella that have biochemical properties similar to it.

Alternatives that can increase the precision and effectiveness of S. enteritidis testing and confirmation include quick molecular-based techniques like real-time PCR. In order to quickly screen for viable S. enteritidis in shell eggs and validate the serotype among the Salmonella colonies, the study set out to create an S. enteritidis PCR method.

The difference in quantification cycle values seen in post-enriched egg cultures allowed the researchers to show that the S. enteritidis real-time PCR can distinguish between viable and non-viable S. enteritidis and confirm the serotype from the Salmonella colonies.

The results show the potential of integrating the S. enteritidis real-time PCR assay into the routine Salmonella testing procedure to speed up the bacteria’s detection in shell eggs.

A total of 89 Salmonella strains from 6 different serogroups were chosen for the study’s artificial inoculation trials and specificity testing.

In the next steps, the researchers inoculated an S. enteritidis colony, spiked homogenized raw eggs with various dilution dosages of live and heat-inactivated S. enteritidis, and homogenized and incubated 73 naturally contaminated shell eggs.

The S. enteritidis was then isolated from the shell eggs and identified using real-time PCR and conventional methods.

The outcomes showed how the S. enteritidis real-time PCR can speed up the detection of the pathogen during the screening of shell eggs and decrease the time-consuming laboratory turnaround required to confirm the serotype of S. enteritidis isolates.

Additionally, the S. enteritidis PCR tests demonstrated good specificity when run on isolates of wild S. enteritidis and well-characterized reference strains.

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