title: Penicillin-susceptible Staphylococcus aureus: susceptibility testing, resistance rates and outcome of infection.
abstract: BACKGROUND
  Staphylococcus aureus (SA) is an important human pathogen that causes both superficial and invasive infections. Penicillin is now rarely used in the treatment of SA infections due to widespread resistance and a concern about the accuracy of existing methods for penicillin susceptibility testing. The aims of the present study were to determine the frequency of penicillin-susceptible SA isolates from blood and wound cultures in Lund, Sweden, and to evaluate methods for penicillin testing in SA. We also wanted to investigate if penicillin-susceptible isolates are associated with higher mortality.
  
  
  METHODS
  Hundred blood culture isolates collected 2008/2009, 140 blood culture isolates from 2014/2015, and 141 superficial wound culture strains from 2015 were examined. Penicillin susceptibility was tested with disk diffusion according to EUCAST guidelines, and results were confirmed with a cloverleaf assay and PCR amplification of the BlaZ gene. Patient data for all bacteraemia cases were extracted from medical records.
  
  
  RESULTS
  The disk diffusion method with assessment of both zone size and zone edge appearance had high accuracy in our study. About 57% of bacteraemia isolates from 2008/2009 were sensitive to penicillin compared to 29% in 2014/2015 (p < .0001). In superficial wound cultures, 21% were penicillin susceptible. There was no difference in co-morbidity or mortality rates between patients with penicillin resistant and penicillin sensitive SA bacteraemia.
  
  
  CONCLUSIONS
  Disk-diffusion is a simple and reliable method to detect penicillin resistance in SA, and susceptibility rates are significant. Penicillin has many theoretical advantages and should be considered in the treatment of SA bacteraemia when susceptible.
authors.affiliation: a Skåne University Hospital , Clinic of Infectious Diseases , Lund , Sweden.|b Division of Infection Medicine, Department of Clinical Sciences Lund , Lund University, Skåne University Hospital , Lund , Sweden.
authors.forename: Malin
authors.initials: M
authors.lastname: Hagstrand Aldman
authors.affiliation: c Division of Laboratory Medicine, Department of Clinical Microbiology , Skåne University Hospital , Lund , Sweden.
authors.forename: Annette
authors.initials: A
authors.lastname: Skovby
authors.affiliation: b Division of Infection Medicine, Department of Clinical Sciences Lund , Lund University, Skåne University Hospital , Lund , Sweden.
authors.forename: Lisa
authors.initials: L
authors.lastname: I Påhlman
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D016470:Bacteremia / Q000382:microbiology; D001426:Bacterial Proteins / Q000235:genetics; D001769:Blood / Q000382:microbiology; D052978:Disk Diffusion Antimicrobial Tests; D024881:Drug Resistance, Bacterial; D005260:Female; D006801:Humans; D008297:Male; D008826:Microbial Sensitivity Tests; D008875:Middle Aged; D010406:Penicillins / Q000494:pharmacology*; D016133:Polymerase Chain Reaction; D013203:Staphylococcal Infections / Q000382:microbiology* / Q000401:mortality; D013211:Staphylococcus aureus / Q000187:drug effects* / Q000235:genetics / Q000302:isolation & purification; D013548:Sweden; D014947:Wounds and Injuries / Q000382:microbiology
chemical_list: D000900:Anti-Bacterial Agents; D001426:Bacterial Proteins; D010406:Penicillins
keywords: Staphylococcus aureus; disk diffusion; mortality; penicillin susceptibility