198 Effects of Bacillus Spp. on Pathogen Inhibition in vitro and on Growth Performance and Bacterial Shedding in Growing Finishing Pigs

Abstract Three experiments (EXP) were conducted to evaluate effectiveness of Bacillus strains on pathogen inhibition in vitro (EXP. 1 and 2) and on growing-finishing pig performance and bacteria shedding (EXP. 3). In EXP. 1, antimicrobial activity of 4 individual Bacillus strains were tested against 9 bacterial pathogens using agar diffusion cross-streak assay. In EXP. 2, a combination of 4 strains (FS4) was evaluated for antimicrobial activity against surrogate strains of the same pathogens in EXP. 1 using well-diffusion and competitive exclusion assays. There were strong inhibitory effects against Streptococcus agalactiae and Staphylococcus aureus aureus with zones of inhibition (ZOI) up to 18.1 and 13.7 mm, respectively. Moderate effects were observed against Listeria monocytogenes, Bordetella bronchiseptica, Escherichia coli, and Salmonella enterica serovar Typhimurium with ZOI up to 8.7, 8.7, 8.1, and 6.3 mm, respectively. On broth, FS4 inhibited Listeria completely (9 log10 CFU/mL) and reduced Staphylococcus by 8 log10 CFU/mL after 24h co-cultivation. In EXP. 3, 236 pigs (initial BW: 33 kg; 6–7 pigs/pen; 17 pens/treatment) were used to evaluate effects of feeding FS4 (7.5 x 104 CFU/g of feed) vs. the control (CON) diets. On d 0, 49, and at market, a pooled fresh fecal sample per pen was obtained for the enumeration of total Salmonella, E. coli, coliform, and Lactobacillus. Feeding FS4 improved (P < 0.05) BW (d 72), ADG (d 43–72 and d 0–72), and Feed:Gain (d 43–72) compared to CON. Overall, pigs fed FS4 were numerically heavier (1.1 kg) than CON pigs. FS4 reduced (P < 0.05) total coliform counts in pigs at market, and numerically reduced E. coli at d 49; however, FS4 had no impact on Lactobacillus. Our data indicate that FS4 had strong inhibitory effects against Streptococcus, Listeria, and Staphylococcus and feeding FS4 improved performance of pigs and lowered coliform shedding without impacting Lactobacillus.