title: Comparison of antibiotic resistance, virulence gene profiles, and pathogenicity of methicillin-resistant and methicillin-susceptible Staphylococcus aureus using a Caenorhabditis elegans infection model.
abstract: OBJECTIVE
  This study compared the presence of 35 virulence genes, resistance phenotypes to 11 anti-staphylococcal antibiotics, and pathogenicity in methicillin-resistant Staphylococcus aureus (MRSA) and methicillin-susceptible S. aureus (MSSA).
  
  
  METHODS
  Multiplex PCR analysis was used to differentiate Staphylococcus aureus isolates (n = 102) based on characterization of the Staphylococcal Cassette Chromosome mec (SCCmec). Singleplex and multiplex PCR assays targeting 35 virulence determinants were used to analyze the virulence repertoire of S. aureus. In vitro activities of the antibiotics were determined by the disk-diffusion method. The pathogenicity of representative isolates was assessed using Caenorhabditis elegans survival assays. Significance in virulence distribution and antibiotic resistance phenotypes was assessed using the Chi-squared tests. Kaplan-Meier survival estimates were used to analyze nematode survival and significance of survival rates evaluated using the log-rank test.
  
  
  RESULTS
  Except for sei (staphylococcal enterotoxin I) (P  =  0·027), all other virulence genes were not significantly associated with MRSA. Resistance to clindamycin (P  =  0·03), tetracycline (P  =  0·048), trimethoprim/sulfamethoxazole (P  =  0·038), and oxacillin (P  =  0·004) was significantly associated with MRSA. Survival assay showed MSSA having a lower median lifespan of 3 days than MRSA that had a median lifespan of 6 days. The difference in the killing time of MRSA and MSSA was significant (P < 0·001).
  
  
  CONCLUSIONS
  While antibiotic resistance was significantly associated with MRSA, there was no preferential distribution of the virulence genes. The quicker killing potential of MSSA compared to MRSA suggests that carriage of virulence determinants per se does not determine pathogenicity in S. aureus. Pathogenicity is impacted by other factors, possibly antibiotic resistance.
authors.forename: Terissa
authors.initials: T
authors.lastname: Thompson
authors.forename: Paul D
authors.initials: PD
authors.lastname: Brown
mesh_terms: D000818:Animals; D017173:Caenorhabditis elegans / Q000382:microbiology; D024881:Drug Resistance, Bacterial; D005798:Genes, Bacterial; D006801:Humans; D055624:Methicillin-Resistant Staphylococcus aureus / Q000187:drug effects / Q000235:genetics / Q000472:pathogenicity; D008826:Microbial Sensitivity Tests / Q000379:methods; D050296:Microbial Viability; D013203:Staphylococcal Infections / Q000382:microbiology*; D013211:Staphylococcus aureus / Q000187:drug effects / Q000235:genetics / Q000472:pathogenicity*; D014774:Virulence / Q000235:genetics
keywords: Antimicrobial resistance,; Caenorhabditis elegans; MRSA,; MSSA,; Virulence,