AUTHOR=Supa-amornkul Sirirak , Mongkolsuk Paninee , Summpunn Pijug , Chaiyakunvat Pongkorn , Navaratdusit Warisara , Jiarpinitnun Chutima , Chaturongakul Soraya 

TITLE=Alternative Sigma Factor B in Bovine Mastitis-Causing Staphylococcus aureus: Characterization of Its Role in Biofilm Formation, Resistance to Hydrogen Peroxide Stress, Regulon Members

JOURNAL=Frontiers in Microbiology

VOLUME=10

YEAR=2019

URL=https://www.frontiersin.org/journals/microbiology/articles/10.3389/fmicb.2019.02493

DOI=10.3389/fmicb.2019.02493

ISSN=1664-302X

ABSTRACT=<p>This study examines treatments of the bacterial pathogen <italic>Staphylococcus aureus</italic>, namely, in the context of its being a major cause of subclinical bovine mastitis. Such infections caused by <italic>S. aureus</italic> among dairy cows are difficult to detect and can easily become chronic, leading to reduced productivity and large losses for dairy manufacturers. In this study, the role of alternative sigma factor B (σ<sup>B</sup>), which has been shown to be a global regulator for <italic>S. aureus</italic> infections, was explored in a mastitis-causing <italic>S. aureus</italic> strain, RF122. For comparison with the wild-type strain, a <italic>sigB</italic> null (Δ<italic>sigB</italic>) mutant was constructed and analyzed for its phenotypes and transcriptome. Our study found that σ<sup>B</sup> is essential for biofilm formation as the Δ<italic>sigB</italic> mutant strain produced significantly less biofilm than did the wild-type strain at 48 h. σ<sup>B</sup> is involved in response to H<sub>2</sub>O<sub>2</sub> stress. However, σ<sup>B</sup> plays a minor or no role in resistance to antiseptics (e.g., povidone-iodine and chlorhexidine), resistance to tested antibiotics, hemolysin activity, and invasion ability. RNA sequencing identified 225 σ<sup>B</sup>-dependent genes, of which 171 are positively regulated and 54 are negatively regulated. The identified genes are involved in stress response, pathogenesis, and metabolic mechanisms. Quantitative TaqMan RT-PCR was performed to verify the RNA sequencing results; i.e., σ<sup>B</sup> is a positive regulator for <italic>asp23, sarA, katA, yabJ, sodA, SAB2006c</italic>, and <italic>nrdD</italic> expressions. In the RF122 strain, σ<sup>B</sup> plays a role in biofilm formation, general stress response (e.g., H<sub>2</sub>O<sub>2</sub>), and regulation of virulence factors and virulence-associated genes.</p>