AUTHOR=Afroj Sayma , Brannen Andrew D. , Nasrin Shamima , Al Mouslem Abdulaziz , Hathcock Terri , Maxwell Herris , Rasmussen-Ivey Cody R. , Sandage Mary J. , Davis Edward W. , Panizzi Peter , Wang Chengming , Liles Mark R. 

TITLE=Bacillus velezensis AP183 Inhibits Staphylococcus aureus Biofilm Formation and Proliferation in Murine and Bovine Disease Models

JOURNAL=Frontiers in Microbiology

VOLUME=12

YEAR=2021

URL=https://www.frontiersin.org/journals/microbiology/articles/10.3389/fmicb.2021.746410

DOI=10.3389/fmicb.2021.746410

ISSN=1664-302X

ABSTRACT=<p>The increasing frequency of <italic>S. aureus</italic> antimicrobial resistance has spurred interest in identifying alternative therapeutants. We investigated the <italic>S. aureus-</italic>inhibitory capacity of <italic>B. velezensis</italic> strains in mouse and bovine models. Among multiple <italic>B. velezensis</italic> strains that inhibited <italic>S. aureus</italic> growth <italic>in vitro</italic>, <italic>B. velezensis</italic> AP183 provided the most potent inhibition of <italic>S. aureus</italic> proliferation and bioluminescence in a mouse cutaneous wound (<italic>P</italic> = 0.02). Histology revealed abundant Gram-positive cocci in control wounds that were reduced in <italic>B. velezensis</italic> AP183-treated tissues. Experiments were then conducted to evaluate the ability of <italic>B. velezensis</italic> AP183 to prevent <italic>S. aureus</italic> biofilm formation on a tracheostomy tube substrate. <italic>B. velezensis</italic> AP183 could form a biofilm on a tracheostomy tube inner cannula substrate, and that this biofilm was antagonistic to <italic>S. aureus</italic> colonization. <italic>B. velezensis</italic> AP183 was also observed to inhibit the growth of <italic>S. aureus</italic> isolates originated from bovine mastitis cases. To evaluate the inflammatory response of mammary tissue to intramammary inoculation with <italic>B. velezensis</italic> AP183, we used high dose and low dose inocula in dairy cows. At the high dose, a significant increase in somatic cell count (SCC) and clinical mastitis was observed at all post-inoculation time points (<italic>P</italic> &lt; 0.01), which resolved quickly compared to <italic>S. aureus-</italic>induced mastitis; in contrast, the lower dose of <italic>B. velezensis</italic> AP183 resulted in a slight increase of SCC and no clinical mastitis. In a subsequent experiment, all mammary quarters in four cows were induced to have grade 1 clinical mastitis by intramammary inoculation of a <italic>S. aureus</italic> mastitis isolate; following mastitis induction, eight quarters were treated with <italic>B. velezensis</italic> AP183 and milk samples were collected from pretreatment and post-treatment samples for 9 days. In groups treated with <italic>B. velezensis</italic> AP183, SCC and abundance of <italic>S. aureus</italic> decreased with significant reductions in <italic>S. aureus</italic> after 3 days post-inoculation with AP183 (<italic>P</italic> = 0.04). A milk microbiome analysis revealed significant reductions in <italic>S. aureus</italic> relative abundance in the AP183-treated group by 8 days post-inoculation (<italic>P</italic> = 0.02). These data indicate that <italic>B. velezensis</italic> AP183 can inhibit <italic>S. aureus</italic> biofilm formation and its proliferation in murine and bovine disease models.</p>