This study was the first national prospective surveillance study assessing antimicrobial activity of meropenem against recent clinical isolates from French hospitals. Antimicrobial susceptibility surveillance studies play a fundamental role in the fight to control resistant organisms. Harmonization between methods and interpretations are important to compare the results of various surveys located in different geographic areas [14, 15]. The EUCAST group has provided progress toward harmonization of susceptibility testing methods used in European Nations and an international consensus on breakpoint definitions. Since 2008, the CA-SFM recommends the EUCAST methods and breakpoints. In this study, we report that meropenem, imipenem and piperacillin/tazobactam are very active against Gram-negative bacilli, including Enterobacteriaceae, P. aeruginosa, Acinetobacter and other non fermenter-bacilli. The susceptibility data obtained from this multicentre study were similar to data previously published for studies conducted in Canada and other European countries [9, 16]. Over the last 5 years, E coli susceptibility worldwide has shown a trend to decrease, in particular to fluoroquinolones and beta-lactams, in relation with the dissemination of CTX-M producers and/or of an increase of AmpC [16–20]. Meropenem and imipenem demonstrate good activity against Enterobacteriaceae, including strains producing ESBLs or AmpC (100% for E coli, 99% for other Enterobacteriaceae), meropenem usually being 2 to 4 fold more potent than imipenem [21–23]. Susceptibility of Acinetobacter was close to 94 to 98% which is similar to other studies reporting susceptibility in Europe and the USA [8, 16]. In this report, piperacillin/tazobactam was the most potent antibiotic against P.aeruginosa (90% of susceptible strains versus 84% for carbapenems) as reported in other studies . Carbapenems as piperacillin/tazobactam showed a very good activity with low MICs against Gram-positive pathogens (MSSCN, MSSA and S. pneumoniae).
Communication of national and regional surveillance data are important to enable local prescribing practices, but in reality, every day antibiotic therapy is based on the sensitivity of antibiotic produced locally. Numerous studies have demonstrated the validity of the Etest method compared to the agar dilution method. The variability of inter-laboratory results is always tested by using reference strains but the statistical analysis of the centre results compared the global data is able to give rise to important informations, it reflects the reality of the daily work. The rate of agreement varies relatively to the antibiotic tested or the bacterial species [24–26]. The agreement (including minor errors) observed between the 2 testing methods was >80% for meropenem, but was low for imipenem (61%). The VME for meropenem were observed in Gram-negative bacilli, whereas there was no difference between Gram-negative bacilli and Gram-positive cocci for imipenem. In general, MIC values obtained using the Etest method were commonly higher than values obtained using agar dilution method. On occasion, interpretation of the MIC could have significant consequences on result reporting (S, I, R) to the physician and subsequent prescribing. Analysis of the VME showed that no particular species was concerned but 2 centres presented VME (p < 0.05). This observation suggested us that it could be due to a local technical problem such as inapropriate storage. Carbapenems and particularly imipenem are unstable antibiotics. The humidity could alter the quality of the strips and could modify the results.