Rapid identification and strain typing of Salmonella

PathoGenetix has announced research demonstrating the use of genome sequence scanning (GSS) technology to confirm and identify pathogenic Salmonella strains in enriched spinach samples in less than five hours. The company detailed its findings at the General Meeting of the American Society for Microbiology in Denver in May.

According to PathoGenetix, the results demonstrate GSS’s ability to shorten the time for pathogen subtyping and serotype determination from an enriched food sample, and to quickly derive additional strain and serotype information from the numerous pathogen screening tests commonly used in the food industry.

Because GSS isolates and scans microbial DNA directly from a mixed culture and does not require a pure culture isolate, it can reduce the time, complexity, skill and cost required by other molecular and whole genome identification approaches, PathoGenetix says. As a result, GSS may enable quicker decisions affecting food safety and public health.

The research spiked ten common Salmonella strains in leafy spinach greens including multiple serotypes of Typhimurium and Enteritidis, as well as the Javiana, Newport, Montevideo and Heidelberg serotypes. The test samples modelled ‘presumptive-positive’ enriched food samples like those that would result from a pathogen screening test indicating the presence of Salmonella. Additional non-Salmonella bacteria were added to half of the test samples to evaluate the technology’s ability to identify and strain type Salmonella in the presence of competing background microorganisms.

Of the 120 samples spiked with Salmonella, GSS positively identified the correct Salmonella serotype in 116 of the samples. Salmonella was not detected in four samples. PathoGenetix says this was due to poor growth of Salmonella in the enrichment of the initial sample, not related to the GSS technology.

The strain type information provided by GSS was comparable to pulsed field gel electrophoresis (PFGE), the current standard for pathogen typing in foodborne outbreak investigation and response. No false positives were recorded from the 12 control samples that had not been spiked with Salmonella.

PathoGenetix also presented research showing that GSS can be used to reliably differentiate and strain type pathogenic E. coli, including the most frequently isolated STEC (Shigatoxin-producing E. coli) serotypes from both sporadic cases and multiple foodborne illness outbreaks.