179. Back to the Future: Penicillin-susceptible Staphylococcus Aureus
Session: Poster Abstract Session: Antimicrobial Stewardship: Current State and Future Opportunities
Thursday, October 8, 2015
Room: Poster Hall
Background: Penicillin was first used to treat septicemia in 1942. Subsequent widespread usage resulted in the emergence of resistance in Staphylococcus aureus. However, new data suggests that penicillin susceptibility may be in a period of renaissance. The objective of our study was to explore the resistance patterns in methicillin-susceptible Staphylococcus aureus(MSSA) bacteremias.

Methods: We retrospectively reviewed all adult MSSA bacteremia from April 2010 to April 2015 at the McGill University Health Centre (Montreal, Canada).  Susceptibility to penicillin, macrolides, clindamycin and trimethoprim-sulfamethoxazole (TMP-SMX) were determined in accordance with the Clinical & Laboratory Standards Institute guidelines.  Only the first positive culture per patient was included.

Results: There were 324 unique episodes of MSSA bacteremia.  90 (28%) isolates were susceptible to penicillin, 229 (71%) to macrolides, 239 (74%) to clindamycin and 317 (98%) to TMP-SMX.  Isolates that were penicillin resistant were more likely to also be resistant to macrolides (76/234 vs. 19/90, p=0.04) but not clindamycin (68/234 vs. 17/90, p=0.06) or trimethoprim-sulfamethoxazole (6/234 vs. 1/90, p=0.42). 

The median age of patients was 67.5 years (IQR 52-78) and overall in-hospital 30-day mortality was 16.3% (53 deaths).  Patients 75 and older were more likely to die (28/99, 28.3%) than those 65-74 (14/82, 17.1%) or below (11/143, 7.7%) (p<0.001). After adjustment for patient age, there was no association between penicillin resistance and either ICU admission or death.

Conclusion: More than one quarter of patients with MSSA bacteremia could be treated with parenteral penicillin. When susceptible, penicillin has prolonged time over minimal inhibitory concentration compared with other beta-lactams: providing a theoretical advantage in achieving cure while minimizing spectrum of activity.  Our results may support a return to penicillin testing among invasive SA isolates in centers that have stopped.

Matthew Pellan Cheng, M.D., C.M., Pierre Rene, MD and Todd C. Lee, MD, Infectious Diseases, McGill University, Montreal, QC, Canada


M. P. Cheng, None

P. Rene, None

T. C. Lee, None

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