243. In Vitro Evaluation of Tigecycline against Drug-Resistant Enterococci and Staphylococcus aureus in North America – TEST 2007 - 2010
Session: Poster Abstract Session: Antimicrobial Susceptibility and Resistance
Friday, October 21, 2011
Room: Poster Hall B1

Background: Tigecycline (TIG), the first marketed drug of the glycylcyclines class of antimicrobials, has been shown to have potent activity against community and hospital acquired staphylococcal and enterococcal pathogens. The TEST program determined the in vitro activity against multidrug-resistant S. aureus and vancomycin-resistant Enterococcus spp. of TIG and 10 antimicrobials commonly prescribed for serious gram-positive infections: amoxicillin-clavulanic acid (AUG), piperacillin-tazobactam (PT), levofloxacin (LVX), ceftriaxone (CAX), minocycline (MIN), vancomycin (VAN), ampicillin (AMP), penicillin (P), and imipenem (IMP).

Methods: A total of 7,080 clinical isolates (2689 enterococci; 4391 S. aureus) were identified to the species level at each participating site and confirmed by a central laboratory. Study strains were collected from 259 laboratories in the United States (234) and Canada (25) throughout 2007-2010.  Minimum Inhibitory Concentrations (MICs) were determined by the local laboratory using broth microdilution panels. Antimicrobial resistance was interpreted according to CLSI breakpoints with TIG susceptible breakpoints defined as ≤0.5 mcg/ml for S. aureus and ≤0.25 mcg/ml for the enterococci.

Results: 20.2% (544/2689) of enterococci were resistant to vancomycin (VRE), and 48.9% (2148/4391) of S. aureus were resistant to cefoxitin (MRSA).  Among the VRE, % resistance rates to other study drugs were LVX 98.7, P 85.7, AMP 85.9, VAN 100, and MIN 20.9.  Resistance rates for MRSA were P 100, AMP 100, AUG 100, LVX 66, PT 100, CAX 100, IMP 100, MIN 0.7, and VAN 0.  TIG inhibited 98.9% of the enterococci and 100% S. aureus resistant to other drugs.  Modal TIG MICs for VRE/NonVRE were 0.06/0.12, respectively, and 0.12/0.12 for MRSA/MSSA, respectively.  Tigecycline inhibited >97% of all MDR enterococci (resistant to 3 or more drug classes) and 100% of MDR S. aureus.

Conclusion: TIG retained potent activity against drug-resistant (including MDR isolates) S. aureus and enterococci, inhibiting 100% of all MRSA and 98.9% of VRE at their defined breakpoints of ≤0.5 and ≤0.25 mcg/ml, respectively.  TIG should prove to be a useful drug for therapy of infections with these resistant gram-positive pathogens.




Subject Category: A. Antimicrobial agents and Resistance

Samuel Bouchillon, MD1, Meredith Hackel, PhD1, Stephen Hawser, PhD2, Brian Johnson, BS1, Daryl Hoban, PhD1 and Michael Dowzicky, MS3, (1)IHMA, Inc., Schaumburg, IL, (2)IHMA Europe Sārl, Epalinges, Switzerland, (3)Pfizer, Inc., Collegeville, PA


S. Bouchillon, Pfizer, Inc.: Consultant, Consulting fee

M. Hackel, Pfizer, Inc.: Consultant, Consulting fee

S. Hawser, Pfizer, Inc.: Consultant, Consulting fee

B. Johnson, Pfizer, Inc.: Consultant, Consulting fee

D. Hoban, Pfizer, Inc.: Consultant, Consulting fee

M. Dowzicky, Pfizer, Inc.: Employee, Salary

Findings in the abstracts are embargoed until 12:01 a.m. EST Thursday, Oct. 20 with the exception of research findings presented at IDSA press conferences.