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Title:   Author  item
                                            Nicholson, Tracy
  Submitted to: American Society for Microbiology General Meeting
                                    Publication Type: Abstract Only
                                    Publication Acceptance Date: 2/1/2012
                                    Publication  Date: 6/16/2012
                                    Citation: Nicholson, T.L. 2012. Swine MRSA isolates form robust biofilms. 112th General Meeting of the American Society for Microbiology. Paper No. 1537. p. 151.Interpretive Summary:
                                Technical Abstract: Background: Methicillin-resistant Staphylococcus aureus (MRSA) colonization of livestock animals is common and prevalence rates for pigs have been reported to be as high as 49%. Measures to prevent, control, or eliminate MRSA in swine is of considerable public health concern. Bacterial colonization of both biological and non-biological surfaces followed by survival or persistence is often linked to the development of attached microbial communities known as biofilms. Community-associated methicillin-resistant S. aureus (CA-MRSA) USA300 strains have recently emerged, causing epidemic outbreaks in humans. These USA300 isolates have been shown to form robust biofilms. Therefore, one hypothesis to explain high prevalence of MRSA in swine herds is the ability of these organisms to exist as biofilms. 
Methods: To investigate the ability of MRSA swine isolates to form biofilms, a microtiter crystal violet assay was used to quantify biofilm formation by several swine and human isolates, including USA300. The contribution of known biofilm matrix components, polysaccharides, proteins and extracellular DNA (eDNA), was tested in all strains as well.
Results: All MRSA swine isolates formed robust biofilms similarly to human clinical isolates, including USA300. The addition of Dispersin B had no inhibitory effect on swine MRSA isolates when added at the initiation of biofilm growth and after pre-established mature biofilms formed. In contrast, the addition of proteinase K inhibited biofilm formation in all strains when added at the initiation of biofilm growth and after pre-established mature biofilms formed. Addition of DNase I at the initiation of biofilm growth inhibited biofilm formation in all strains, albeit with varied degrees of reduction. DNase I treatment of pre-established mature biofilms failed to disrupt biofilm biomass in all swine MRSA isolates.
Conclusion: Swine MRSA isolates form robust biofilms and the biofilm matrix produced by these isolates is significantly composed of proteins and not polysaccharides or polysaccharide intercellular adhesion (PIA). These findings parallel reports for other MRSA isolates, including USA300. Additionally, eDNA is a component of the biofilm matrix, however the contribution of eDNA remains unclear given that not all pre-established mature biofilms produced by swine MRSA isolates were disrupted after DNase I treatment. Collectively, these findings provide a critical first step in designing strategies to control or eliminate MRSA in swine herds.


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