Genome level distinguishing features order SC144 identified in human MRSA and LA-MRSA isolates include mobile genetic elements (MGEs), such as the immune evasion cluster (IEC) of genes carried on the 13 family of bacteriophage, which are found in nearly all human isolates, but rarely found in LA-MRSA isolates [44?6] LA-MRSA strains, largely comprising MLST type ST398, currently represent the largest reservoir of MRSA outside of a BL-8040 cost hospital setting [47]. Therefore, strategies to eliminate or decrease the prevalence of these strains in swine herds are a public health priority. Outside of the previously mentioned in vitro binding assays [44], no other phenotypic studies have been undertaken to specifically investigate virulence or survival mechanisms associated with LA-MRSA strains. It is well established that biofilm formation is an important contributing factor in chronic human infections caused by S. aureus. Biofilms are adherent communities of bacteria encased within a complex matrix that protects the encased bacterial community from a variety of environmental stresses such as shear flow forces, antimicrobial compounds, and host immune and clearance mechanisms [48,49]. We hypothesized that if biofilms are an important survival trait for this species, then this phenotype will be conserved in LA-MRSA strains. In this study, we examined a collection of methicillin-sensitive S. aureus (MSSA) and MRSA isolates of different sequence types (STs) from swine and retail meat sources for their ability to form biofilms. Given the genotypic and phenotypic differencesobserved between human MRSA and LA-MRSA isolates, we then compared the biofilms formed by the LA-MSSA and LAMRSA strains to biofilms formed by laboratory MSSA and MRSA strains and human MRSA isolates, including HA-MRSA (USA100) and CA-MRSA (USA300) strains. To gain further insights into the mechanisms responsible for biofilm development, we additionally tested the contribution of known biofilm matrix components, polysaccharides, proteins and extracellular DNA (eDNA), in these LA-MRSA strains.Materials and MethodsBacterial Strains and Growth ConditionsThe bacterial strains used in this study are listed in Table 1. S. aureus strains were grown in tryptic soy broth (BectonDickinson, Sparks, MD) supplemented with 0.5 glucose and 3 NaCl (TSB-GN). Staphylococcus epidermidis strains were grown in tryptic soy broth supplemented with 0.5 glucose (TSB-G). All strains were grown at 37?C and maintained on tryptic soy agar plates (Becton-Dickinson, Sparks, MD).Microtiter Plate Assay for Biofilm FormationBiofilm formation was assessed using a microtiter plate assay as previously described [50,51], except the surface of the microtiter plates used were coated with porcine plasma to increase biofilm adherence to the plate ( [50,51]; data not shown). Briefly, Costar 3596 plates (Corning Life Sciences, Lowell, MA) were coated with lyophilized porcine plasma (Sigma, St. Louis, MO) by incubating each well with 100 of a 20 porcine plasma solution in 0.05M carbonate-bicarbonate buffer (pH 9.6) overnight at 4?C. The plasma solution was removed from the plate immediately prior to use. Overnight cultures of all strains were diluted to an OD600 of 0.05 in fresh media and 100 was added to each well. For each experimental plate, 3 wells were used for each strain representing one biological replicate. The plates were incubated statically for 24 hours in a humidified 37?C incubator. The cultures were aspirated from the p.Genome level distinguishing features identified in human MRSA and LA-MRSA isolates include mobile genetic elements (MGEs), such as the immune evasion cluster (IEC) of genes carried on the 13 family of bacteriophage, which are found in nearly all human isolates, but rarely found in LA-MRSA isolates [44?6] LA-MRSA strains, largely comprising MLST type ST398, currently represent the largest reservoir of MRSA outside of a hospital setting [47]. Therefore, strategies to eliminate or decrease the prevalence of these strains in swine herds are a public health priority. Outside of the previously mentioned in vitro binding assays [44], no other phenotypic studies have been undertaken to specifically investigate virulence or survival mechanisms associated with LA-MRSA strains. It is well established that biofilm formation is an important contributing factor in chronic human infections caused by S. aureus. Biofilms are adherent communities of bacteria encased within a complex matrix that protects the encased bacterial community from a variety of environmental stresses such as shear flow forces, antimicrobial compounds, and host immune and clearance mechanisms [48,49]. We hypothesized that if biofilms are an important survival trait for this species, then this phenotype will be conserved in LA-MRSA strains. In this study, we examined a collection of methicillin-sensitive S. aureus (MSSA) and MRSA isolates of different sequence types (STs) from swine and retail meat sources for their ability to form biofilms. Given the genotypic and phenotypic differencesobserved between human MRSA and LA-MRSA isolates, we then compared the biofilms formed by the LA-MSSA and LAMRSA strains to biofilms formed by laboratory MSSA and MRSA strains and human MRSA isolates, including HA-MRSA (USA100) and CA-MRSA (USA300) strains. To gain further insights into the mechanisms responsible for biofilm development, we additionally tested the contribution of known biofilm matrix components, polysaccharides, proteins and extracellular DNA (eDNA), in these LA-MRSA strains.Materials and MethodsBacterial Strains and Growth ConditionsThe bacterial strains used in this study are listed in Table 1. S. aureus strains were grown in tryptic soy broth (BectonDickinson, Sparks, MD) supplemented with 0.5 glucose and 3 NaCl (TSB-GN). Staphylococcus epidermidis strains were grown in tryptic soy broth supplemented with 0.5 glucose (TSB-G). All strains were grown at 37?C and maintained on tryptic soy agar plates (Becton-Dickinson, Sparks, MD).Microtiter Plate Assay for Biofilm FormationBiofilm formation was assessed using a microtiter plate assay as previously described [50,51], except the surface of the microtiter plates used were coated with porcine plasma to increase biofilm adherence to the plate ( [50,51]; data not shown). Briefly, Costar 3596 plates (Corning Life Sciences, Lowell, MA) were coated with lyophilized porcine plasma (Sigma, St. Louis, MO) by incubating each well with 100 of a 20 porcine plasma solution in 0.05M carbonate-bicarbonate buffer (pH 9.6) overnight at 4?C. The plasma solution was removed from the plate immediately prior to use. Overnight cultures of all strains were diluted to an OD600 of 0.05 in fresh media and 100 was added to each well. For each experimental plate, 3 wells were used for each strain representing one biological replicate. The plates were incubated statically for 24 hours in a humidified 37?C incubator. The cultures were aspirated from the p.
