ABSTRACT Non-typhoidal Salmonella (NTS) is the leading cause of deaths associated with foodborne illnesses in the United States. NTS is primarily transmitted in humans through the consumption of contaminated poultry and poultry products. Antibiotics and vaccines are used to control Salmonella infection in poultry. However, the evolution of antibiotic-resistant Salmonella and the lack of cross-protection by vaccines necessitate the development of novel antimicrobials for Salmonella infection. Antimicrobial peptides are considered viable alternatives due to the reduced propensity for resistance development, broad-spectrum activity, and lower toxicity. Our previous study detected 33 small peptides in the culture supernatants of Lacticaseibacillus rhamnosus GG and Bifidobacterium lactis (Bb12). Among them, we characterized the efficacy of two peptides (PN3 and PN5) against Salmonella in vitro and in vivo . Our results demonstrated that PN3 and PN5 inhibited the growth of Salmonella Typhimurium (ST) and nine other Salmonella serotypes. PN3 was cidal to ST within 30 min of incubation, and PN5 in 8 h in the time-kill kinetics assay. Additionally, both peptides completely cleared intracellular ST and ST inside the biofilm. PN3 and PN5 possessed stability at high temperatures and against proteolytic enzyme. In resistance assays, ST did not acquire resistance to both peptides. PN3 and PN5 were non-toxic to wax moths and increased their survivability and reduced ST load following challenge. Moreover, the oral administration of PN3 and PN5 significantly reduced ST load in the cecum of infected chickens. Overall, our study showed that PN3 and PN5 are promising candidates to control Salmonella infection in poultry. IMPORTANCE Non-typhoidal Salmonella (NTS) is the leading cause of foodborne-associated deaths in the United States, with 420 deaths reported annually. Although antibiotics are used to control NTS invasive infection, overuse of antibiotics has accelerated the evolution of multidrug-resistant (MDR) Salmonella , necessitating the development of novel alternatives to antibiotics. Antimicrobial peptides (AMPs) are promising alternatives to antibiotics due to their activity against MDR Salmonella , lower chances of acquiring resistance, selectivity, and stability. This study investigated the effect of two AMPs, PN3 and PN5, against Salmonella . Our results demonstrated that PN3 and PN5 inhibit the growth of Salmonella , are stable at higher temperatures, and are resistant to proteolytic enzyme activity. Salmonella exposed to peptides were not prone to acquire resistance. Peptides were effective against Salmonella in the wax moth model and chickens. This study characterized two AMPs identified previously with potential for developing a novel approach to control Salmonella in poultry, prevent foodborne illnesses, and mitigate the rising antimicrobial resistance problem.
Bhandari et al. (Fri,) studied this question.