Salmonella in the spotlight

Study investigating Salmonella serotypes in Saudi Arabia could lead to a reduction in food-borne illness, and the development of a vaccine. 

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A KAIMRC-led study has identified S. Enteritidis and S. Typhimurium as the two most common Salmonella serotypes treated in a Riyadh hospital between 2015 and 2017.  This observation aligns with global Salmonella serotype data.

The bacterial pathogen Salmonella is a leading cause of food-borne illness. Eggs, chicken, fruit, vegetables, and processed foods can harbour the bacteria. An estimated 1.35 million cases of human infections are reported each year in the United States, resulting in 26,500 hospitalizations and 420 deaths. So far, data on the prevalence and type of Salmonella infections in Saudi Arabia has been scarce. 

Now, researchers including Majed Alghoribi and Michel Doumith at KAIMRC’s Infectious Diseases Research Department (IDRD,) along with colleagues in Canada, have begun to address this knowledge gap. 

“Our study1 is the first of its kind to examine the prevalence of Salmonella serotypes — groups of bacteria that share distinctive surface structures — associated with human infections in Saudi Arabia,” says corresponding author Taseen Desin at the University of Saskatchewan. “Along with other work being done at the KAIMRC IDRD, our findings will lead to the development of better surveillance and intervention measures in the country, which will result in lower human infections and a safer food supply.”

The team analysed 200 Salmonella clinical isolates collected between 2015 and 2017 at a hospital in Riyadh. The samples were taken from patients with symptoms ranging from gastrointestinal illness to whole-body (systemic) infection. Using a rapid testing kit called Check and Trace Salmonella™, they found that S. Enteritidis was the most prevalent at 40%, followed by  S. Typhimurium (13.5%) and three other serotypes called S. Livingstone (5%), S. Kentucky and S. Poona (both at 4.5%). 

As S. Enteritidis and S. Typhimurium are the two most common serotypes in other parts of the world, including the US and Europe, Desin says the findings fit well with global Salmonella serotype data, although he cautions that further tests based on data collected nationally would be needed to confirm that this is the case. 

Country-level disparities in the prevalence of less common serotypes could be accounted for by differences in eating habits, geographical location and climate, the researchers say.

The team tested for the presence of two virulence determinants considered to be hallmarks of Salmonella infection. “The majority of strains we examined contained these determinants, called SPI-1 and SPI-2,” explains Desin. “We found that SPI-2 was absent in some of the strains that did not cause systemic infection.” This observation aligns with previous studies pointing to SPI-2’s involvement in the systemic spread and survival of the bacteria in host organs. 

The role of SPI-1 is less clear. It continues to be a topic of discussion following a study2, by Qinghua Hu and co-workers, that showed SPI-1 was absent from two strains isolated from an outbreak in Shenzhen, China, in 2002.

The fact that the study uncovered the presence of a multidrug-resistant S. Kentucky strain for the first time in Saudi Arabia is a concerning issue that poses challenges for physicians limited in their choice of treatment options. “Importantly, our work will enable us to develop a database of the antibiotic profiles of all Salmonella strains in the country along with their associated serotypes,” says Desin. 

References

  1. Alghoribi, M. F., Doumith, M., Alrodayyan, M., Al Zayer, M., Köster, W. L. et al. , S. Enteritidis and S. Typhimurium harboring SPI-1 and SPI-2 are the predominant serotypes associated with human salmonellosis in Saudi Arabia. Frontiers in Cellular and Infection Microbiology 9:187 (2019) | article

    2. Hu, Q., Coburn, B., Deng, W., Li, Y., Shi, X., et al. Salmonella enterica serovar Senftenberg human clinical isolates lacking SPI-1. Journal of Clinical Microbiology 46, 1330–1336 (2008).  | article

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