Salmonella strain finding shows more to learn
Researchers from Texas Tech University’s Department of Animal and Food Sciences in the College of Agricultural Sciences and Natural Resources discovered the serotype, which has been named Salmonella Lubbock because of the city in which it was discovered.
The finding by Marie Bugarel, a research assistant professor in the department, will improve the accuracy with which Salmonella is subtyped.
Human effect found over time
Human susceptibility to the Lubbock strains remains unknown but Guy Loneragan, a professor of food safety and public health, said this will be found out over time.
“As public health labs start updating the way they classify serotypes based on Marie’s discovery, we will learn if some of those ones that might have been called Salmonella Montevideo in the past, for example, are in fact Salmonella Lubbock,” he told FoodQualityNews.
“If, with improved classification, they start reporting Salmonella Lubbock associated with human disease, that question will be answered.”
Loneragan believes between 20 and 30% of two current strains, Salmonella Montevideo and Salmonella Mbandaka, will be reclassified as Salmonella Lubbock.
The work has led to a patent application licensed to a biosciences research company but the pair told us the firm is still developing the assay for the equipment so it was premature to name it.
Bugarel said the team would like to understand the genetic characteristics of strains isolated from lymph nodes that make them able to persist and survive in comparison to Salmonella strains present in feces.
“To do so, we sequenced the genome of eight strains isolated from both sources and previously serotyped as Montevideo. By comparing the whole genome sequences, we saw that two out of the eight strains were different,” she said.
“The first thing we saw that the sequences of the antigens were not consistent with what they should be for a Montevideo serotype.”
The team worked with the Food Safety laboratory of France (ANSES) to confirm the presence of the antigens at the bacterial surface.
Then the strains were sent to the Salmonella reference laboratory at the Pasteur Institute in France and after confirmation, they sent the strains to two other reference laboratories as having confirmation of the new serotype by three reference laboratories is required for official recognition.
Rapid detection tools
Bugarel has worked on developing new tools to detect the pathogen, approaches to distinguish serotypes and ways to understand the biology.
Using whole genome sequences, the researchers were able to identify a DNA sequence specific to Lubbock serotype.
They developed a molecular marker that allows the identification of Lubbock strains and to properly attribute the serotype to mis-classified Montevideo or Mbandaka strains.
Her invention means it is possible to simultaneously detect and distinguish specific strains of Salmonella by targeting a specific combination of DNA.
This will allow for early detection in food while identifying whether or not it belongs to a highly pathogenic strain.
The standard way of distinguishing one strain from another is called serotyping and is based on the molecules on the surface of the bacterium.
Each serotype has its own pattern of molecules, called antigens, and the collection of molecules provides a unique molecular appearance. These antigens interact with certain antibodies found in specifically prepared serum, providing the serotype.
It appears that for a while, we have been inadvertently classifying the subtype, said Longeragan.
“The more we can be accurate in putting Salmonella into correct subtypes it will help with research and also investigations if there is animal or public health outbreaks with Salmonella,” he said.
“More broadly, however, the discovery ought to inform us that there is more to be learned about Salmonella and in particular, how Salmonella has evolved to different ecological niches.
“For example, a better understanding of Salmonella Lubbock and other serotypes that we commonly recover from cattle will help enable us to understand why they occur commonly and how to discover effective control strategies.”
The researchers said they will continue to investigate the new strain to better understand its genetic characteristics in the survival and persistence into lymph nodes.
