Abstract
BackgroundBiofilm formation by Staphylococcus aureus is an important virulence attribute because of its potential to induce persistent antibiotic resistance, retard phagocytosis and either attenuate or promote inflammation, depending upon the disease syndrome, in vivo. This study was undertaken to evaluate the potential significance of strength of biofilm formation by clinical bovine mastitis-associated S. aureus in mammary tissue damage by using a mouse mastitis model.MethodsTwo S. aureus strains of the same capsular phenotype with different biofilm forming strengths were used to non-invasively infect mammary glands of lactating mice. Biofilm forming potential of these strains were determined by tissue culture plate method, ica typing and virulence gene profile per detection by PCR. Delivery of the infectious dose of S. aureus was directly through the teat lactiferous duct without invasive scraping of the teat surface. Both bacteriological and histological methods were used for analysis of mammary gland pathology of mice post-infection.ResultsHistopathological analysis of the infected mammary glands revealed that mice inoculated with the strong biofilm forming S. aureus strain produced marked acute mastitic lesions, showing profuse infiltration predominantly with neutrophils, with evidence of necrosis in the affected mammary glands. In contrast, the damage was significantly less severe in mammary glands of mice infected with the weak biofilm-forming S. aureus strain. Although both IL-1β and TNF-α inflammatory biomarkers were produced in infected mice, level of TNF-α produced was significantly higher (p<0.05) in mice inoculated with strong biofilm forming S. aureus than the weak biofilm forming strain.ConclusionThis finding suggests an important role of TNF-α in mammary gland pathology post-infection with strong biofilm-forming S. aureus in the acute mouse mastitis model, and offers an opportunity for the development of novel strategies for reduction of mammary tissue damage, with or without use of antimicrobials and/or anti-inflammatory compounds for the treatment of bovine mastitis.
Highlights
Histopathological analysis of the infected mammary glands revealed that mice inoculated with the strong biofilm forming S. aureus strain produced marked acute mastitic lesions, PLOS ONE | DOI:10.1371/journal.pone
The damage was significantly less severe in mammary glands of mice infected with the weak biofilm-forming S. aureus strain. Both IL-1β and TNF-α inflammatory biomarkers were produced in infected mice, level of TNF-α produced was significantly higher (p
Despite advances in diagnosis and management practices aimed at reducing the incidence of ruminant mastitis associated with the contagious pathogens, Staphylococcus aureus (S. aureus) is one of the major contagious causative agents of clinical and subclinical bovine mastitis worldwide causing significant economic loss to the dairy industry [1,2,3]
Summary
Despite advances in diagnosis and management practices aimed at reducing the incidence of ruminant mastitis associated with the contagious pathogens, Staphylococcus aureus (S. aureus) is one of the major contagious causative agents of clinical and subclinical bovine mastitis worldwide causing significant economic loss to the dairy industry [1,2,3]. Reduced milk production due to mastitis is associated with irreversible mammary tissue damage in majority of the cases [4]. Once the organism enters into the mammary gland, it adheres to epithelial cell receptors for bacterial adhesins [8] resulting in the production of virulence factors mentioned above and intracellular uptake of the small colony variants of S. aureus. Mammary tissue damage is further compounded by various toxins and extracellular enzymes produced by S. aureus, including α, β, γ, and δ toxins, toxic shock syndrome toxin (TSST-1), enterotoxins, nuclease, coagulase, catalase, hyaluronidase, phosphatase, lipase, staphylokinase and proteases [9]. This study was undertaken to evaluate the potential significance of strength of biofilm formation by clinical bovine mastitis-associated S. aureus in mammary tissue damage by using a mouse mastitis model
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