Abstract
BackgroundStaphylococcus aureus is associated with chronic mastitis in cattle, and disease manifestation is usually refractory to antibiotic therapy. Biofilm production is a key element of S. aureus pathogenesis and may contribute to the treatment failure that is consistently reported by veterinarians. Minas Gerais State is the largest milk-producing state in Brazil, and the characterization of bacterial isolates is an important aspect of disease control for dairy farmers. Here, we investigated the potential of S. aureus isolated from bovine mastitis to produce slime and biofilm in a skim-milk medium and classified the isolates according to their agr type.ResultsSlime was detected using the Congo Red agar (CRA) test in 35.18% (19/54) of the strains; however, 87.04% (47/54) of the strains were considered biofilm-positive based on crystal violet staining. Compared to TSB supplemented with 0.25% glucose, skim milk significantly increased the production of biofilm, but this effect was only observed in slime-producing strains. The bacteria belonged to agr groups I (12/54), II (34/54), III (6/54), and IV (2/54), and bacteria in agr group III were found to be stronger biofilm producers than those in groups I and II. Again, milk had a significant influence only on slime-positive agr I and II isolates, revealing an association between milk and slime.ConclusionsThe present study demonstrated that skim-milk medium and slime production are two factors that together influence biofilm formation by bovine strains of S. aureus. A predominance of bacteria belonging to agr group II was observed, and bacteria from agr group III showed the highest proportion of biofilm producers. The majority of bacteria characterized in this study formed biofilm in milk, which suggests that biofilm formation has an important role in the virulence of S. aureus isolated from bovine intramammary infections.
Highlights
Staphylococcus aureus is associated with chronic mastitis in cattle, and disease manifestation is usually refractory to antibiotic therapy
Streptococcus agalactiae was used as a negative control for slime and biofilm production due to the phenotype of its colonies on Congo Red agar (CRA; redsmooth colonies) and because it showed the same optical density (OD630) value as the medium without bacteria in microplate assays
“Slime formation” was once the term used for biofilm formation [23]; if we revisit the review published by Hall-Stoodley et al [24], slime is defined as the extracellular polymeric substance, known as Extracellular polymeric substance (EPS), that is mainly formed by polysaccharide intercellular adhesion (PIA) in S. epidermidis and S. aureus, DNA and proteins can be found in this material
Summary
Staphylococcus aureus is associated with chronic mastitis in cattle, and disease manifestation is usually refractory to antibiotic therapy. In Brazil, which is considered by the Food and Agriculture Organization (FAO) as the fourth largest milk producer in the world [1], S. aureus infections are a major concern with respect to the welfare of dairy cattle The presence of this pathogen in a dairy herd was first reported in Brazil in 1978 by Muller et al [2]; since the pathogen has been found. Simojoki et al [10] evaluated nearly 200 coagulase-negative staphylococci associated with bovine mastitis and found that neither biofilm nor slime production are correlated with persistent infection Another complaint by veterinarians is the low efficacy of antimicrobial treatments for infections caused by S. aureus [7], it has been reported that inhibiting bacterial biofilm production reduces bacterial resistance in in vivo assays [11]. Beenken et al [12] demonstrated that reduced biofilm production by S. aureus in a murine model was correlated with increased susceptibility to daptomycin
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