Abstract
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%. Mechanisms contributing to the persistent carriage and high prevalence rates of livestock-associated methicillin-resistant Staphylococcus aureus (LA-MRSA) strains in swine herds and production facilities have not been investigated. One explanation for the high prevalence of MRSA in swine herds is the ability of these organisms to exist as biofilms. In this report, the ability of swine LA-MRSA strains, including ST398, ST9, and ST5, to form biofilms was quantified and compared to several swine and human isolates. The contribution of known biofilm matrix components, polysaccharides, proteins and extracellular DNA (eDNA), was tested in all strains as well. All MRSA swine isolates formed robust biofilms similar to human clinical isolates. The addition of Dispersin B had no inhibitory effect on swine MRSA isolates when added at the initiation of biofilm growth or 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 was able to disperse pre-established mature biofilms. Of the LA-MRSA strains tested, we found ST398 strains to be the most sensitive to both inhibition of biofilm formation and dispersal of pre-formed biofilms by DNaseI. Collectively, these findings provide a critical first step in designing strategies to control or eliminate MRSA in swine herds.
Highlights
Staphylococcus aureus is an opportunistic pathogen that can cause serious disease in humans, ranging from skin and soft tissue infections to invasive infections of the bloodstream, heart, lungs and other organs [1]
Previous reports have shown that consistent biofilm formation by human clinical strains can be obtained by using tryptic soy broth medium supplemented with 0.5% glucose and 3% NaCl (TSB-GN) and using polystyrene microtiter plates pre-coated with 20% human plasma [50,57]
Since biofilm formation by a range of strains was supported by growth in TSB-GN on 20% porcine plasma-coated microtiter plates, these conditions were chosen for all subsequent assays
Summary
Staphylococcus aureus is an opportunistic pathogen that can cause serious disease in humans, ranging from skin and soft tissue infections to invasive infections of the bloodstream, heart, lungs and other organs [1]. It is frequently carried asymptomatically on the skin and in the anterior nares. In the mid-1990s, new strains of MRSA emerged, causing infections in healthy individuals who had no recent contact with healthcare facilities [7]. CAMRSA has spread worldwide and is beginning to replace HA-MRSA strains in healthcare facilities [5,9]
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