Faster salmonella test boosts food safety for people, animals

Test improves diagnosis time to 24 hours versus as long as five days using current procedures.

A new test allows accurate, rapid testing for salmonella, a bacteria that is one of the leading causes of foodborne illness across all regions of the world, according to Cornell University, which helped develop the test.

Salmonella can infect animals as well as people, with commonly reported cases of people falling sick after handling pets and livestock.

Tests that used to take days now take 24 hours, with a hundred-fold improvement in detection for at least one type, Salmonella Dublin, that is an emerging concern and is difficult to grow in culture, making its diagnosis difficult.

The new method, first developed for automated food safety testing and then adapted by Cornell scientists for a wider range of sample types, can detect the bacteria from environmental and clinical samples, including swabs, feces, milk and blood.

The new test improves diagnosis time versus current procedures, which can take as long as five days, according to a recent study published Sept. 1 in the Journal of Veterinary Diagnostic Investigation.

"Because we have this 24-hour turnaround time with the new test, there are veterinary hospitals and clinics that can test and get results rapidly and make sure they are not exposing other animals to salmonella," said Belinda Thompson, assistant clinical professor at Cornell's Animal Health Diagnostic Center and a senior author of the paper.

Fast clinical diagnoses allow veterinarians to quickly quarantine an infected animal.

S. Dublin is "host adapted" in cattle, meaning infected animals can become permanent or long-term carriers, putting herd mates -- especially susceptible calves -- at risk. This strain can infect people who may be exposed by contact with infected animals, by drinking raw milk or by consuming other contaminated food products. In humans, S. Dublin causes systemic infection of body tissues, similar to typhoid, and leads to higher hospitalization and fatality rates than other salmonella types.

"Salmonella bio-surveillance in veterinary facilities is critical because animals can shed the bacteria without showing clinical disease signs," said lead author of the study Laura Goodman, a senior research associate in the Cornell department of population medicine and diagnostic sciences.

The study describes an important innovation: Choosing a type of broth culture that selectively provides the right nutrients to grow certain bacteria. The researchers chose a broth that would cover a wide range of salmonella types, including S. Dublin and others relevant to animal health. They then applied an advanced molecular detection system to screen the broth for small amounts of salmonella DNA. Bacteria can be further characterized with whole-genome sequencing.

“Salmonellosis can be a serious and costly disease of animals and people, and anything we can do to enhance diagnostic procedures to help control the pathogen is a good thing,” Thompson said.

Goodman added that the method described in the study is now available as an environmental testing program through the Animal Health Diagnostic Center.

The test was funded and developed in collaboration with the Food & Drug Administration's Veterinary Laboratory Investigation & Response Network. Cornell works closely with FDA scientists to evaluate and perform new methods that the government agency can then share with other veterinary labs.

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