title: Back to the Future: Penicillin-Susceptible Staphylococcus aureus.
abstract: BACKGROUND
  Widespread penicillin usage rapidly resulted in the emergence of penicillin resistance in Staphylococcus aureus. However, new data suggest that penicillin susceptibility may be in a period of renaissance. The objective of our study was to quantify penicillin resistance in methicillin-susceptible Staphylococcus aureus (MSSA) bacteremia.
  
  
  METHODS
  We retrospectively reviewed all adult MSSA bacteremia from April 2010 to April 2015 at the McGill University Health Centre (Montreal, QC, Canada). Susceptibility to penicillin, erythromycin, clindamycin, and trimethoprim-sulfamethoxazole (TMP-SMX) was determined in accordance with the Clinical & Laboratory Standards Institute guidelines.
  
  
  RESULTS
  There were 324 unique episodes of MSSA bacteremia. Ninety (28%) isolates were susceptible to penicillin, 229 (71%) to erythromycin, 239 (74%) to clindamycin, and 317 (98%) to TMP-SMX. Isolates that were penicillin resistant were more likely to also be resistant to other antibiotics, but a statistically significant association was apparent only for erythromycin resistance (76/234, 32.2% vs 19/90, 21.1%, P = .04). The median age of patients was 67.5 years (interquartile range 52-78) and overall in-hospital 30-day mortality was 16.3% (53 deaths). After adjustment for patient age, there was no association between penicillin resistance and either intensive care unit admission or death.
  
  
  CONCLUSIONS
  More than one-quarter of patients with MSSA bacteremia potentially could be treated with parenteral penicillin, which may offer pharmacokinetic advantages over other beta-lactam drugs and potentially improved outcomes.
authors.affiliation: Division of Infectious Diseases and Department of Medical Microbiology, McGill University Health Centre, Montréal, Quebec, Canada. Electronic address: matthew.cheng@mail.mcgill.ca.
authors.forename: Matthew P
authors.initials: MP
authors.lastname: Cheng
authors.affiliation: Division of Infectious Diseases and Department of Medical Microbiology, McGill University Health Centre, Montréal, Quebec, Canada.
authors.forename: Pierre
authors.initials: P
authors.lastname: René
authors.affiliation: École Polytechnique de Montréal, Montréal, Quebec, Canada.
authors.forename: Alexandre P
authors.initials: AP
authors.lastname: Cheng
authors.affiliation: Division of Infectious Diseases and Department of Medical Microbiology, McGill University Health Centre, Montréal, Quebec, Canada; Division of General Internal Medicine and Department of Medicine, McGill University Health Centre, Montréal, Quebec, Canada.
authors.forename: Todd C
authors.initials: TC
authors.lastname: Lee
mesh_terms: D061605:Administration, Intravenous; D000368:Aged; D000900:Anti-Bacterial Agents / Q000008:administration & dosage / Q000494:pharmacology / Q000627:therapeutic use; D016470:Bacteremia / Q000188:drug therapy* / Q000382:microbiology / Q000401:mortality; D024901:Drug Resistance, Multiple, Bacterial; D006801:Humans; D007902:Length of Stay; D008826:Microbial Sensitivity Tests; D008875:Middle Aged; D010403:Penicillin Resistance; D010406:Penicillins / Q000008:administration & dosage / Q000494:pharmacology / Q000627:therapeutic use*; D011792:Quebec / Q000453:epidemiology; D012189:Retrospective Studies; D013203:Staphylococcal Infections / Q000188:drug therapy* / Q000401:mortality; D013211:Staphylococcus aureus / Q000187:drug effects*
chemical_list: D000900:Anti-Bacterial Agents; D010406:Penicillins
keywords: Penicillin; Staphylococcus aureus; Susceptible