In a new study, experts delved into the physical forces that guide a multidrug-resistant strain of salmonella to evolve strategies for invading the body.

Fine-Tuning Infection Tactics

Pathogens have evolved complex mechanisms to invade their hosts' bodies. They have the ability to flourish in hostile conditions and even resist immune defenses. In a recent study, a team of experts from Arizona State University (ASU) explored the factors that guide this behavior in a strain of salmonella.

In the paper "Incremental increases in physiological fluid shear progressively alter pathogenic phenotypes and gene expression in multidrug resistant Salmonella," the ASU team investigates how disease-causing microorganisms like salmonella adapt their disease characteristics under fluid shear conditions. These are the same as the conditions they encounter in the human body during infection.

Led by Professor Cheryl Nickerson, the team collaborated with experts from the University of Cincinnati and NASA Johnson Space Center. They used mathematical modeling and laboratory investigations of bacterial cultures to investigate the changes in the genes and disease-causing traits of salmonella typhimurium under various physiological fluid shear environments.

There are over 2,600 types of salmonella which are known for causing food-borne illnesses. However, only a small part of the population causes infections in humans, which they do so with impressive frequency.

In this study, the scientists focused their investigations on salmonella typhimurium ST313 strain D23580. This strain is involved in highly invasive bacterial infection in sub-Saharan Africa and in other parts of the world.

Nickerson and colleagues explored fluid shear forces by using a rotating wall vessel bioreactor to culture salmonella typhimurium strain D23580. They modified the specialized bioreactor to mimic a broader range of fluid shear conditions that will likely be encountered by the bacteria inside the human body.

This approach enabled the researchers to simulate and quantify various fluid shear conditions, from the low fluid shear in the intestinal tract to high fluid shear in the bloodstream during sepsis.

This study is the first to demonstrate that gradual changes in fluid shear forces change immune cell survival, stress responses, colonization of human intestinal cells, and global gene expression in the ST313 strain. This provides insights into how such forces could affect the ability of bacteria to survive and cause disease.

READ ALSO: Clever Salmonella Found a Way of Evading Plant Defenses and Sneaking Into Salads

What Is Fluid Shear?

Bacteria usually live in dynamic fluid environments, with flow affecting basic microbial processes like nutrient uptake. Fluids can encounter shear stress, which is the amount of force applied to a fluid parallel to a very small surface element.

Fluid shear refers to the mechanical force driven by fluid flow, like those that take place along the walls of blood vessels or over the surfaces of cells in the intestine. It influences the behavior of bacteria and their interaction with host cells during infection in ways that are not observed when they are grown under laboratory conditions.

For instance, fluid shear can have an impact on the ability of bacteria to adhere to and invade the tissues of their host. This can have a significant effect on the development and progression of a disease.

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