Vancomycin, Teicoplanin, Linezolid and Daptomycin MICs for Methicillin- Resistant Staphylococcus aureus and Coagulase-Negative Staphylococci: P1569 comparison of broth microdilution and E-test® methods M.DESROCHES 1,2 , J. POTIER 1,2 , F. JEHL 3, G. LINA 4, R. LECLERCQ 5, F. VANDENESH 6, Y. RIO 7, J-W. DECOUSSER 1, F. DOUCET- POPULAIRE 1,2 and the MICROBS Group. 1: service de Bactériologie-Hygiene, AP-HP, CHU Antoine Béclère, Clamart France ; 2: EA 4043, USC INRA, Université Paris-Sud, Châtenay-Malabry France ; 3: CHRU, Strasbourg ; 4,6: Centre National de Référence, Lyon ; 5: CHU, Caen ; 7: CHR, Metz
Introduction and objective Methods Selecting empirical treatment for staphylococci invasive infections is based on Our study, called MICROBS, is a French prospective, multicenter study (37 centers). evaluation of the prevalence of resistance. MICs determination needs technical control Antimicrobial activity of vancomycin, teicoplanin, linezolid and daptomycin were due to the importance of strains categorization, and therapeutic choice. Broth determined by BMD (Sensititre/Trek) according to CLSI recommendations and by E-test ® Microdilution method (BMD) is the reference method but E-test ® method is daily use in according to the manufacturer's instructions (Biomérieux) on Muller-Hinton agar (Biorad). A laboratory . Some intravenous antibiotics are subjects to be monitored because of the calcium supplement (50 mg/L final concentration) was used for testing daptomycin staphylococcal emergence of resistance, as vancomycin and teicoplanin susceptibility by BMD. (glycopeptides), linezolid and daptomycin. The aim of our study was to compared E- BMD was considered as the reference method for MICs determination. test ® method and BMD for evaluating the activity of 4 intravenous antimicrobial agents: Essential agreements (EA) (the percentage of isolates MIC by Etest within 1 doubling vancomycin, teicoplanin, linezolid and daptomycin. dilution of the MIC by BMD) were calculated.
Results
367 methicillin-resistant Staphylococcus aureus (MRSA) and 704 coagulase-negative Table 1. Comparaison of vancomycin, teicoplanin, linezolid and daptomycin MICs staphylococci (CoNS) isolates from severe infections were included between October 2011 by BMD and E-test® for 1071 staphylococcus clinical isolates and February 2012. 197 MRSA (54%) and 446 CoNS (63%) were isolated from bloodstream infections 170 MRSA and 258 CoNS were isolated from other infections including respectively 136 (37%) and 172 (24%) from bone and joint infections.
1- MRSA. When the MIC50/MIC90 were studied, vancomycin and teicoplanin MICs were slightly overestimated by E-test ® for MRSA. Whereas linezolid and daptomycin MICs were underestimated by E-test ® in comparison to BMD. For linezolid and daptomycin, E-test ® produced MICs values 1-2 times lower than BMD. 2- CoNS . When the MIC 50 /MIC 90 were studied, there was no difference for vancomycin and teicoplanin MICs between the 2 methods. MICs underestimated by E-test ® for linezolid and daptomycin There was just an exception concerning the linezolid mean MIC for CoNS, which was greater by E-test ® method determination (while E-test ® method underestimated the values of linezolid MICs). It is due to the extensive range of E-test ® values (up to 256 mg/L).
Conclusion References In our study, all essential agreements were acceptable except for daptomycin (MRSA and CoNS) due to the dispersion of the low MICs values. (1) Is Vancomycin MIC creep method dependent ? Analysis of methicillin resistant ® ® Staphylococcus aureus susceptibility trends in blood isolates from North East Scotland Vancomycin and teicoplanin MICs were slightly overestimated by E-test , whereas linezolid and daptomycin MICs were underestimated by E-test from 2006 to 2010. Edwards et al. J Clin Microbiol. 2012. 50: 318-325 in comparison to BMD. (2) Correlation of methicillin resistant Staphylococcus aureus vancomycin minimal inhibitory concentration results by E-test® and broth microdilution methods with population analysis profile : lack of E-test® overstimation of the MIC. Khatib et al. Eur J This data are similar to previous publications for vancomycin (1) and linezolid (2). Gomez-Garces et al . have already lifted the question of Clin Microbiol Infect Dis. 2013. doi 10.1007/s10096-012-1811-7 discrepant daptomycin MICs between the two methods (3), while Nakashima et al. showed that MICs determination depends of calcium (3) Estudio comparativo de Wider, E-test® y microdilucion para la determinacion de la sensibilidad a daptomicina y otros tres antimicrobianos de aislamientos clinicos de Staphylococcus spp. Resistantes a meticillina y Enterococcus spp. Gomez-Garces et al. concentration in MH agar (4). The freezing of isolates could also modified the MIC values. Rev Esp Quimoter 2010 23 :87-92 However, E-test may be more suitable than conventional BMD for MIC outcome assessment because of the easy of use and the more detailed (4) Daptomycin Etest MICs for methicillin-resistant Staphylococcus aureus vary among different media.Nakashima et al.J Infect Chemother 2012;18:970-2. MICs.