E ST398 strains. In four strains (Newman, 29213, SH1000 and 43300), no protease activity was detected in the conditioned medium from either biofilm or planktonic cultures. S. aureus strain MN135 and S. epidermidis strain NJ9709 each had a modest level of protease activity in the biofilm culture medium, albeit significantly less than in their respective planktonic culture medium.Extracellular nuclease productionAs extracellular DNA is an important component of S. aureus biofilms, we tested the strains for production of secreted nucleases when grown as biofilm and planktonic cultures. APLOS ONE | www.plosone.orgSwine MRSA Isolates form Robust BiofilmsTable 3. Biofilm biomass reduction by DNaseI.Inhibition Strain USA100 AZD4547 site MRS1008 MN55 USA300 MN56 MRS879 TCH1516 MRS935 T2(T2TGT) MN06 T3(TGT) IA97 MRS926 P2(HPH1) MRS913 NJ101 HU01011N HU01010T MRS910 MRS927 IA91 MN48 IA63 MN135 MRS922 ST 5 5 9 8 9 5 8 5 398 5 398 398 398 398 398 398 398 398 398 398 398 398 398 398 398 Reduction 2 15 26 30 32 38 39 42 49 61 62 63 66 67 69 70 72 73 76 76 78 80 81 82 83Dispersal Strain USA100 USA300 MRS1008 TCH1516 MRS935 MN56 MN55 MRS879 T2(T2TGT) IA97 MN06 MRS913 T3(TGT) MRS910 P2(HPH1) HU01011N HU01010T MN48 MRS926 MRS927 IA91 NJ101 IA63 MRS922 MN135 ST 5 8 5 8 5 9 9 5 398 398 5 398 398 398 398 398 398 398 398 398 398 398 398 398 398 Reduction 9 21 36 37 38 47 49 53 62 77 78 85 87 90 90 91 91 93 93 93 93 94 94 94 95clear zone surrounding the point of inoculation was observed for the majority of the S. aureus strains in both biofilm and planktonic culture medium (Figure 10), indicating the presence of a secreted nuclease in the samples. A small number of S. aureus strains exhibited low nuclease activity in both culture types: SH1000, MN55, MN56 and USA100. The remaining strains, including all ST398 strains, exhibited higher nuclease activity in both biofilm and planktonic culture medium. The S. epidermidis strains 1457 and NJ9709 did not produce a secreted nuclease as expected, since S. epidermidis does not possess the nuc genes [75]. Comparing conditioned planktonic culture medium (Figure 10A) to conditioned biofilm culture medium (Figure 10B) showed that for all strains that the presence or absence of nuclease activity was the same in both culture types, i.e. if a strain produced nuclease in planktonic culture, it also produced it in biofilm culture. Interestingly, the strains with the least detectable nuclease activity (S. aureus SH1000, MN55, MN56, USA100, S. epidermidis 1457 and NJ9709), were also among the least sensitive to biofilm formation inhibition and biofilm dispersal by DNaseI (Table 3, Figure 3, Figure 6).DiscussionThe spread of MRSA is a serious public health concern for both human and veterinary medicine. LA-MRSA strains,predominately consisting of ST398 isolates, currently represent the largest PD150606 site reservoir of MRSA outside of hospitals [47]. Thus, strategies to eliminate or decrease the prevalence of these strains in swine and other livestock populations are a public health priority. While numerous studies have demonstrated the presence of MRSA ST398 in livestock, there are few studies addressing the virulence properties of these strains. Moreover, to our knowledge, mechanisms contributing to the persistent carriage and high prevalence rates of LA-MRSA strains in swine herds and production facilities have not been investigated. In this report, we tested the ability of swine LAMSSA and LA-MRSA st.E ST398 strains. In four strains (Newman, 29213, SH1000 and 43300), no protease activity was detected in the conditioned medium from either biofilm or planktonic cultures. S. aureus strain MN135 and S. epidermidis strain NJ9709 each had a modest level of protease activity in the biofilm culture medium, albeit significantly less than in their respective planktonic culture medium.Extracellular nuclease productionAs extracellular DNA is an important component of S. aureus biofilms, we tested the strains for production of secreted nucleases when grown as biofilm and planktonic cultures. APLOS ONE | www.plosone.orgSwine MRSA Isolates form Robust BiofilmsTable 3. Biofilm biomass reduction by DNaseI.Inhibition Strain USA100 MRS1008 MN55 USA300 MN56 MRS879 TCH1516 MRS935 T2(T2TGT) MN06 T3(TGT) IA97 MRS926 P2(HPH1) MRS913 NJ101 HU01011N HU01010T MRS910 MRS927 IA91 MN48 IA63 MN135 MRS922 ST 5 5 9 8 9 5 8 5 398 5 398 398 398 398 398 398 398 398 398 398 398 398 398 398 398 Reduction 2 15 26 30 32 38 39 42 49 61 62 63 66 67 69 70 72 73 76 76 78 80 81 82 83Dispersal Strain USA100 USA300 MRS1008 TCH1516 MRS935 MN56 MN55 MRS879 T2(T2TGT) IA97 MN06 MRS913 T3(TGT) MRS910 P2(HPH1) HU01011N HU01010T MN48 MRS926 MRS927 IA91 NJ101 IA63 MRS922 MN135 ST 5 8 5 8 5 9 9 5 398 398 5 398 398 398 398 398 398 398 398 398 398 398 398 398 398 Reduction 9 21 36 37 38 47 49 53 62 77 78 85 87 90 90 91 91 93 93 93 93 94 94 94 95clear zone surrounding the point of inoculation was observed for the majority of the S. aureus strains in both biofilm and planktonic culture medium (Figure 10), indicating the presence of a secreted nuclease in the samples. A small number of S. aureus strains exhibited low nuclease activity in both culture types: SH1000, MN55, MN56 and USA100. The remaining strains, including all ST398 strains, exhibited higher nuclease activity in both biofilm and planktonic culture medium. The S. epidermidis strains 1457 and NJ9709 did not produce a secreted nuclease as expected, since S. epidermidis does not possess the nuc genes [75]. Comparing conditioned planktonic culture medium (Figure 10A) to conditioned biofilm culture medium (Figure 10B) showed that for all strains that the presence or absence of nuclease activity was the same in both culture types, i.e. if a strain produced nuclease in planktonic culture, it also produced it in biofilm culture. Interestingly, the strains with the least detectable nuclease activity (S. aureus SH1000, MN55, MN56, USA100, S. epidermidis 1457 and NJ9709), were also among the least sensitive to biofilm formation inhibition and biofilm dispersal by DNaseI (Table 3, Figure 3, Figure 6).DiscussionThe spread of MRSA is a serious public health concern for both human and veterinary medicine. LA-MRSA strains,predominately consisting of ST398 isolates, currently represent the largest reservoir of MRSA outside of hospitals [47]. Thus, strategies to eliminate or decrease the prevalence of these strains in swine and other livestock populations are a public health priority. While numerous studies have demonstrated the presence of MRSA ST398 in livestock, there are few studies addressing the virulence properties of these strains. Moreover, to our knowledge, mechanisms contributing to the persistent carriage and high prevalence rates of LA-MRSA strains in swine herds and production facilities have not been investigated. In this report, we tested the ability of swine LAMSSA and LA-MRSA st.