Professor Margie Lee | Combating Salmonella Infection by Exploring Microbial Competition in Chicken Guts

While Salmonella threatens day-old chicks whose gut microbiomes lack diversity, older chickens with developed microbiomes can resist infection. To protect young chicks from Salmonella infection, they are often given probiotic treatments. But how these treatments work is poorly understood. By experimentally exposing Salmonella to a commercial competitive exclusion product in the laboratory, Lee’s team was able to observe how other microbes can suppress or aid the proliferation of Salmonella.

They found that at least 3 mechanisms of exclusion take place when Salmonella enters the chicken gut microbiome. Microbes in the chicken gut compete for nutrients, particularly sugars. The researchers found fewer sugars available for Salmonella to consume in the presence of a competitive exclusion product.

Nevertheless, Salmonella bacteria appeared to survive by consuming the waste products of other bacteria. By consuming these waste products, Salmonella would help to maintain a favorable environment for other gut bacteria, indicating a cooperative relationship.

However, the team also discovered several mechanisms that other microbes employ to suppress Salmonella. Microbes produce substances that hinder Salmonella growth and the expression of genes linked to host-cell invasion. These microbes increase levels of avrA, an anti-inflammatory and anti-virulence factor, further suppressing the proliferation of Salmonella. In a pivotal finding, Lee’s team identified that a currently unknown type of bacteria produces an antimicrobial substance called polyketide synthase, which may inhibit Salmonella growth.

Regulatory hurdles have often led to the usage of single-species probiotics for poultry, despite the availability of multispecies products, such as the one used by Lee’s team. The team’s research shows that single-species probiotics lack the diversity required to target Salmonella effectively. Equipped with this knowledge, probiotic manufacturers and poultry farmers can recognize that a range of bacteria is needed to fend off Salmonella, each one playing an essential role in their ecosystem.