Flavophospholipol: Effect on multi-drug resistant Salmonella enterica serovar Typhimurium in swine

Objectives: To assess the effect of flavophospholipol on Salmonella shedding and antimicrobial resistance via a plasmid-curing mechanism. Materials and methods: Fifty-six pigs (60 days old) that tested negative by culture for Salmonella were allocated into four treatment groups and challenged with either Salmonella serovar Typhimurium DT104 or Salmonella Typhimurium DT193. After challenge, each treatment group was fed one of four feed rations: a ration containing no antimicrobials (Control) or the same ration containing either flavophospholipol (F), penicillin and chlortetracycline (PCt), or penicillin, chlortetracycline, and flavophospholipol (PCtF). Fecal samples were obtained weekly for 20 weeks (three samples pre-challenge and 17 post challenge) and processed for Salmonella isolation and antimicrobial-resistance testing. Results: For pigs challenged with phage type DT193, the duration of Salmonella shedding was significantly shorter in the PCtF group than in the controls, with a hazard ratio (HR) of 4.51 (P = .01). Overall, shedding time was significantly shorter in pigs challenged with DT104 than in those challenged with DT193 (HR 13.6; P < .001). The proportions of both DT104 and DT193 isolates resistant to ampicillin and amoxicillin-clavulanic acid were significantly lower after treatment with flavophospholipol. Implications: Growth-promotion levels of antimicrobials can decrease the shedding time of S Typhimurium in clinically healthy animals. Use of in-feed flavophospholipol may result in loss of resistance of S Typhimurium to certain classes of antimicrobials.