Research Note: Virulence gene downregulation and reduced intestinal colonization of Salmonella enterica serovar Typhimurium PHL2020 isolate in broilers by a natural antimicrobial (NeutraPath™)

Abstract

The reduction in antibiotic growth promoter use in poultry, due to antibiotic resistance concerns, has created a need for natural solutions that control enteric pathogens like Salmonella. One of these natural feed additives, a select blend of essential oils, fatty acids, and an enterosorbent mineral (NeutraPath), was assessed for its effects on the intestinal colonization of Salmonella enterica serovar Typhimurium PHL2020 isolate (ST-PHL2020) in broiler chickens and ST-PHL2020 virulence gene expression. An in vitro digestion model simulating the pH and enzymatic conditions of 3 gastrointestinal compartments (crop, proventriculus, and intestine) was first used to evaluate the antibacterial effects of NeutraPath on ST-PHL2020. For the in vivo study, day-old male broilers (n = 90) were randomly allocated to 1 of 3 groups: control or NeutraPath supplemented at 0.25 or 0.5%. The dose rates were chosen to enable observable statistical effects during high Salmonella challenge. All groups were challenged with ST-PHL2020 (106 cfu/bird) via oral gavage on day 9. Bacterial load and prevalence of ST-PHL2020 were examined in ceca-cecal tonsils, and intestinal permeability was assessed via serum recovery of fluorescein isothiocyanate dextran (FITC-d) 24 h postchallenge. NeutraPath inhibited (P < 0.05) ST-PHL2020 growth in the in vitro digestion model compared to the control at all concentrations and in all compartments other than NeutraPath 0.25% in the crop. In vivo, NeutraPath 0.25 and 0.5% reduced (P < 0.05) the total cfu recovered and total prevalence of ST-PHL2020 in the ceca. The serum FITC-d levels were also reduced (P < 0.05) by NeutraPath. Further, NeutraPath's effects on ST-PHL2020’s Salmonella pathogenicity island-1 virulence network development were explored via treating ST-PHL2020 at subinhibitory concentration (1 mg/mL) of NeutraPath in vitro. Compared to the control, NeutraPath downregulated ST-PHL2020 hilA and invF mRNA expression, which further blocked expression of key downstream effectors involved in ST-PHL2020 invasion. Collectively, NeutraPath has the potential to reduce ST-PHL2020 intestinal colonization in broilers and preserve intestinal barrier integrity.