Slide

Glycopeptide MICs are Higher in MSSA compared with MRSA
from Blood in the UK and Ireland 2001-2009
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R. Reynolds1, R. Hope2 and The BSAC Extended Working Party on Resistance Surveillance1 1British Society for Antimicrobial Chemotherapy, Birmingham, B1 3NJ 2Health Protection Agency, London, NW9 5HT BACKGROUND
MSSA infections, best treated with a -lactam, may be treated empirically with an anti-MRSA agent if there is a risk of MRSA infection. MIC distributions for anti-MRSA agents are of particular concern as clinical outcomes with vancomycin treatment may be worse when isolates have raised MICs (below the breakpoint, but above the mode).
Vertical bars for each antimicrobial show results for the years 2001-2009, in order.
25 laboratories across the UK and Ireland supplied up to 20 Horizontal bars show the estimated mean for all years tested.
S. aureus from blood each year (previously 10, 2001-2007) to the BSAC Resistance Surveillance Project. MICs were measured centrally by the BSAC agar dilution method and The MIC difference between MRSA and MSSA for VAN, TEC, distributions compared between MRSA and MSSA by TLV and TGC was consistently in the same direction every year .
interval regression on log MIC. Differences were expected for ceftobiprole, which targets the penicillin binding protein conferring resistance in MRSA, but not for other agents In the following graphs, positive values show MSSA having higher MICs, or more MICs above the mode, than MRSA.
• MICs for MRSA were 1.5 dilutions (2.9-fold) higher than Difference in % with MIC above mode, MSSA-MRSA The mode MIC was also 2 (vs. 0.5), and the maximum MIC of 4 mg/L was seen in only 4/726 MRSA.
Other anti-MRSA agents (see graphs and tables) • All had good in vitro activity with narrow unimodal MIC distributions. Non-susceptibility was <1% (except 1.5% • MICs for TGC were significantly lower for MSSA than for MRSA; LZD and DAP MICs showed no differences.
• VAN, TEC and TLV MICs were slightly, but very
consistently and statistically significantly, higher for
CONCLUSIONS
MSSA than for MRSA.
• Glycopeptide MICs were slightly but significantly higher for • Correspondingly, the proportion of isolates with
MSSA than MRSA (mostly EMRSA15 in the UK and Ireland) glycopeptide MICs raised above the mode was 12 to
19 percentage points higher in MSSA.
• A higher proportion of MSSA had ‘raised but susceptible’ MICs.
Abbreviations: VAN vancomycin, TEC teicoplanin, TLV telavancin, LZD linezolid, DAP daptomycin, TGC tigecycline, BPR ceftobiprole.
• This may contribute to poor outcome when MSSA infections are Testing periods: VAN, TEC, LZD 2001-09; TGC 2002-09; BPR 2003-09; DAP 2003, 2005-07, 2009; TLV 2005-09.
treated empirically with vancomycin.
Working Party Members (August 2010): A. MacGowan1 (Chair), M. Allen2, D. Biek3, D. Brown4, R. Hope5,
Central Laboratory: Health Protection Agency, London.
D. Lewis6, D. Livermore5, E. Lee7, K. Maher8, I. Morrissey8, K. Pagano9, J. Porter10, R. Reynolds1, C. Sponsors 2001-2009: Astellas, AstraZeneca, Cerexa, Cubist, Johnson&Johnson,
MSD, Novartis, Pfizer, Theravance. Support: BSAC.
Organism ID and Susceptibility Testing: R. Hope5 and staff at HPA.
Correspondence: Dr. R. Reynolds, BSAC Resistance Surveillance Coordinator.
Department of Medical Microbiology, Southmead Hospital, Bristol, BS10 5NB, UK.
Collecting Laboratories: See www.bsac.org.uk or White 2008, JAC 62 (Suppl 2) ii3 - ii14
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1North Bristol NHS Trust ; 2Novartis; 3Cerexa; 4EUCAST Scientific Secretary; 5Health Protection Agency, London ; 6HPA South West ; 7Janssen Pharmaceutica; 8Quotient Bioresearch Ltd., Microbiology; 9Astellas; 10Pfizer; 11Tony White Ltd.
www.bsac.org.uk

Source: http://bsacsurv.co.uk/uploads/publications/publications/2010_ICAAC_bact_vancMICs.pdf