266. Title: Daptomycin Non-Susceptible Staphylococcus aureus
Session: Poster Abstract Session: Antimicrobial Susceptibility and Resistance
Friday, October 21, 2011
Room: Poster Hall B1
Background: 

Daptomycin (DAP) has bactericidal activity against most Gram positive pathogens; non-susceptibility has been consistently ≤ 0.2 % among S. aureus (SA) isolates. We report 10 confirmed cases of DAP non-susceptible SA (DNSSA) from our institution in 2010.

Methods: 

SA isolates with a DAP MIC ≥ 2 µg/ml by Vitek-2 underwent confirmatory testing by broth microdilution and Etest. Chromosomal DNA analysis by pulsed field gel electrophoresis (PFGE) was performed. Demographics, comorbidities, microbiologic data, and clinical course were reviewed.

Results: 

Thirteen isolates were identified by Vitek-2 as potential DNSSA; 10 were confirmed by broth microdilution and Etest. This represented 0.37% of all SA isolates from our institution in 2010. PFGE was performed on 9 isolates; two USA 600, one USA 100, five USA 300, one non-typable. Infections included skin and soft tissues (4), bacteremia (3), diskitis/epidural abscess (2), and intra-abdominal infection (1). Two isolates were MSSA and eight were MRSA. Four of the DNSSA isolates had a vancomycin MIC of 2 µg/ml, the remaining 6 isolates had MICs ≤ 1 µg/ml. One isolate had a linezolid MIC = 4 µg/ml, all other isolates had MIC ≤ 2 µg/ml. No link was found among the patients. At the time of DNSSA discovery, 4 and 3 patients had recent or ongoing therapy with DAP or vancomycin, respectively. One patient treated with DAP despite confirmed non-susceptibility failed therapy. Remaining cases were successfully treated after surgical intervention (if applicable) and alternative antibiotics including minocycline, linezolid, quinupristin/dalfopristin and clindamycin. Only 1 patient died during hospitalization (due to C. difficile).

Conclusion: 

To our knowledge this is the largest annual collection of DNSSA from a single institution. Though half the isolates were USA 300, this was not a clonal outbreak and there was no link between patients. Further molecular analysis is needed to better understand the resistance mechanism in these isolates. Though DNSSA remains uncommon, susceptibility to DAP should always be confirmed.


Subject Category: A. Antimicrobial agents and Resistance

Alexander Velazquez, MD1, C. Andrew DeRyke, Pharm.D.1,2, Valerie J. Hoover, MTASCP3, Dina Besece, PharmD4 and Mark R. Wallace, MD1, (1)Infectious Diseases, Orlando Health, Orlando, FL, (2)Pharmacy, Orlando Health, Orlando, FL, (3)Microbiology Laboratory, Orlando Health, Orlando, FL, (4)Cubist Pharmaceuticals , Lexington, MA

Disclosures:

A. Velazquez, None

C. A. DeRyke, None

V. J. Hoover, None

D. Besece, Cubist Pharmaceuticals: Employee, Salary

M. R. Wallace, None

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