Abstract
This study examines treatments of the bacterial pathogen Staphylococcus aureus, namely, in the context of its being a major cause of subclinical bovine mastitis. Such infections caused by S. aureus 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 (σB), which has been shown to be a global regulator for S. aureus infections, was explored in a mastitis-causing S. aureus strain, RF122. For comparison with the wild-type strain, a sigB null (ΔsigB) mutant was constructed and analyzed for its phenotypes and transcriptome. Our study found that σB is essential for biofilm formation as the ΔsigB mutant strain produced significantly less biofilm than did the wild-type strain at 48 h. σB is involved in response to H2O2 stress. However, σB 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 σB-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., σB is a positive regulator for asp23, sarA, katA, yabJ, sodA, SAB2006c, and nrdD expressions. In the RF122 strain, σB plays a role in biofilm formation, general stress response (e.g., H2O2), and regulation of virulence factors and virulence-associated genes.
Highlights
Bovine mastitis is an inflammation of the mammary gland (Viguier et al, 2009), which negatively impacts the dairy industry, leading to economic losses due to reduced milk production and increased treatment expenses (Wall et al, 2005; Le Maréchal et al, 2011b)
SigB strain in RF122 was constructed, and the role of σB in stress response was assessed by comparing the phenotypes of the wild type to those of the mutant
We propose that the role of σB on biofilm formation in mastitiscausing S. aureus is ica independent
Summary
Bovine mastitis is an inflammation of the mammary gland (Viguier et al, 2009), which negatively impacts the dairy industry, leading to economic losses due to reduced milk production and increased treatment expenses (Wall et al, 2005; Le Maréchal et al, 2011b). Staphylococcus aureus is one of the most prevalent causative agents of subclinical and clinical mastitis (Dego et al, 2002; Azizoglu et al, 2013). The inability to rapidly detect subclinical mastitis leads to a high prevalence of such infections being observed in dairy farms (Gruet et al, 2001). Antibiotic-resistant S. aureus, relating to β-lactam drugs, has been reported among mastitis-causing strains (Gruet et al, 2001). Alternative treatments (e.g., anti-CD40 monoclonal antibody) or novel drug targets (e.g., transcription factors) are needed strategies to combat bovine mastitis (Wallemacq et al, 2012)
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