Program Schedule

Tracking Linezolid Antimicrobial Activity and Resistance in North America: Results from LEADER 2013 Program

Session: Poster Abstract Session: Surveillance of Antimicrobial Resistance
Thursday, October 9, 2014
Room: The Pennsylvania Convention Center: IDExpo Hall BC
Background: The LEADER Program has monitored the activity of linezolid (LZD) and comparator agents in USA medical centers since 2004.  The percent of non-susceptible (NS) Gram-positive (GP) monitored isolates has remained below 1% (range, 0.14-0.45%; 0.17% in 2012).

Methods: In 2013, a total of 7,183 GP pathogens were sampled from 60 medical centers across the USA. Isolates were susceptibility (S) tested by CLSI reference broth microdilution methods.  LZD NS isolates were confirmed by repeated reference S testing, with the LZD Etest  (bioMerieux, Hazelwood, Missouri, USA) and CLSI disk diffusion methods.   


A total of 3,035 S. aureus strains were submitted. Methicillin-resistant S. aureus (MRSA; 47.9%)  varied from 35.1% (Middle Atlantic) to 58.7% (East South Central). Resistance rates among MRSA for many antimicrobial agents were much higher than in MSSA. Examples included the β-lactam agents, levofloxacin (MRSA, 64.2%, MSSA, 11.2%), clindamycin (26.7%, 5.3%), and erythromycin (87.8%, 31.9%).  The LZD MIC50/90 for S. aureus was 1/1 μg/ml (S, 99.9%). There were two LZD NS isolates (MRSA from California and Michigan); both contained cfr and L3 mutations. The MIC50 and modal MIC for MRSA and MSSA were the same. A total of 580 CoNS isolates exhibited a LZD MIC50/90 at 0.5/1 μg/ml (S, 99.5%).  The three LZD NS CoNS isolates contained mutations at 23S rRNA and L3 and/or L4.  LZD was active against Enterococci with a MIC50/90 at 1/1 μg/ml and 99.4% S. All LZD NS enterococci had a G2476T mutation and one also contained a cfr. S to LZD for 399 viridans group streptococci (VGS) and 964 β-hemolytic streptococci was 99.7 and 100.0%, respectively. There was one S. sanguinis isolate (LZD NS [MIC, 4 μg/ml]), which demonstrated a mutation at the G2576 nucleotide of the 23S rRNA.  LZD S for all organisms tested (7,183) was 99.83% with only 12 isolates (6 Enterococci, 2 S. aureus,3 S. epidermidis, 1 VGS) testing NS. 

Conclusion: LZD among USA medical centers demonstrated excellent activity and a sustained S rate of 99.83%. LZD MIC population distributions remain stable without evidence of “MIC creep” among monitored species. These data show no evidence of widespread dissemination of the cfr resistance determinant in LEADER Program monitored USA medical centers.

Robert K. Flamm, PhD1, Jennifer M. Streit, BS1, James E. Ross, MBA1, Rodrigo E. Mendes, PhD1, Ronald N. Jones, MD1 and Patricia Hogan2, (1)JMI Laboratories, North Liberty, IA, (2)Pfizer Inc, Collegeville, PA


R. K. Flamm, Pfizer Inc.: Grant Investigator, Research grant

J. M. Streit, Pfizer Inc.: Grant Investigator, Research grant

J. E. Ross, Pfizer Inc.: Grant Investigator, Research grant

R. E. Mendes, Pfizer Inc.: Grant Investigator, Research grant

R. N. Jones, Pfizer Inc.: Grant Investigator, Research grant

P. Hogan, Pfizer Inc.: Employee, Salary

Findings in the abstracts are embargoed until 12:01 a.m. EDT, Oct. 8th with the exception of research findings presented at the IDWeek press conferences.

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