AUTHOR=Vaillancourt Katy , Frenette Michel , Gottschalk Marcelo , Grenier Daniel 

TITLE=Streptococcus pluranimalium 2N12 Exerts an Antagonistic Effect Against the Swine Pathogen Actinobacillus pleuropneumoniae by Producing Hydrogen Peroxide

JOURNAL=Frontiers in Veterinary Science

VOLUME=8

YEAR=2021

URL=https://www.frontiersin.org/journals/veterinary-science/articles/10.3389/fvets.2021.787241

DOI=10.3389/fvets.2021.787241

ISSN=2297-1769

ABSTRACT=<p><italic>Actinobacillus pleuropneumoniae</italic> is the causal agent of porcine pleuropneumonia, a highly contagious and often deadly respiratory disease that causes major economic losses in the swine industry worldwide. The aim of the present study was to investigate the hydrogen peroxide (H<sub>2</sub>O<sub>2</sub>)-dependent antagonistic activity of <italic>Streptococcus pluranimalium</italic> 2N12 (pig nasal isolate) against <italic>A. pleuropneumoniae</italic>. A fluorimetric assay showed that <italic>S. pluranimalium</italic> produces H<sub>2</sub>O<sub>2</sub> dose- and time-dependently. The production of H<sub>2</sub>O<sub>2</sub> increased in the presence of exogenous lactate, suggesting the involvement of lactate oxidase. All 20 strains of <italic>A. pleuropneumoniae</italic> tested, belonging to 18 different serovars, were susceptible to H<sub>2</sub>O<sub>2</sub>, with minimal inhibitory concentrations and minimal bactericidal concentrations ranging from 0.57 to 2.3 mM. H<sub>2</sub>O<sub>2</sub>, as well as a culture supernatant of <italic>S. pluranimalium</italic>, killed planktonic cells of <italic>A. pleuropneumoniae</italic>. Treating the culture supernatant with catalase abolished its bactericidal property. H<sub>2</sub>O<sub>2</sub> was also active against a pre-formed biofilm-like structure of <italic>A. pleuropneumoniae</italic> albeit to a lesser extent. A checkerboard assay was used to show that there were antibacterial synergistic interactions between H<sub>2</sub>O<sub>2</sub> and conventional antibiotics, more particularly ceftiofur. Based on our results and within the limitations of this <italic>in vitro</italic> study, the production of H<sub>2</sub>O<sub>2</sub> by <italic>S. pluranimalium</italic> could be regarded as a potential protective mechanism of the upper respiratory tract against H<sub>2</sub>O<sub>2</sub>-sensitive pathogens such as <italic>A. pleuropneumoniae</italic>.</p>