Antimicrobial Peptides Stave Off Salmonella in Chickens

Salmonella bacteria pose serious public health threats as a common cause of foodborne illness in the United States, most often from consumption or handling of poultry products.¹ Because chickens and turkeys can carry the bacteria without showing any signs of infection, farmers often used to treat these animals with antibiotics. However, this practice negatively impacts gut health in poultry and greatly contributes to antimicrobial resistance, leading to antibiotic use being phased out.^2,3 Yet the need to control Salmonella to prevent foodborne illness remains a challenge.

One potential alternative to antibiotics is antimicrobial peptides (AMPs), short strings of amino acids that can inhibit bacterial growth, often by disrupting bacterial membranes. A team of researchers at the University of Illinois Urbana-Champaign and The Ohio State University tested the ability of AMPs made by one bacterial species against Salmonella enterica subsp. enterica serovar Typhimurium LT2 (ST) in vitro and in chickens. In a study published in Microbiology Spectrum, they identified two AMPs that reduced ST levels in the animals, offering a promising proof of concept for the future of AMP-based treatment for public health.⁴

The team first evaluated six AMPs produced by the bacterial species Lactobacillus rhamnosus GG for their ability to inhibit the growth of ST in vitro. From these, they identified four candidates. All of these AMPs also reduced growth of other Salmonella variants, called serovars, that cause foodborne illness, supporting broadly anti-Salmonella activity. The researchers also showed that these AMPs retained their antimicrobial effects at high temperature and after treatment with protease, which are industry requirements.

To evaluate the candidate peptides anti-Salmonella effects in vivo, they treated chickens with each AMP for one week. Three days into the trial, the researchers infected the animals with ST and determined how much of the bacteria remained seven days later. Two of the AMPs significantly reduced the amount of ST in the cecum, part of the intestine. The researchers also showed that the AMPs did not affect microbial diversity in the chickens’ intestines.

Finally, to explore how the AMPs impeded bacterial growth, the team studied how the two most successful AMPs affected ST’s membrane by confocal microscopy and transmission electron microscopy. Unlike the defined, intact membrane in untreated controls, bacteria treated with either AMP had evidence of membrane disruption.

“This study could provide a framework for developing and using antimicrobial peptides to control Salmonella in chickens, thereby promoting food safety and public health. Our future work is to test these peptides in chickens on a large scale, optimize their delivery in water and/or feed, understand better how they kill Salmonella, and explore more peptides like these for their anti-Salmonella activity,” said study author and University of Illinois Urbana-Champaign microbiologist Gireesh Rajashekara in a press statement.