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ABSTRACTThis study determined the performance of BD Max StaphSR and the rate of methicillin-resistant Staphylococcus aureus(MRSA) with an unrecognized staphylococcal cassette chromosome mec(SCCmec) right-extremity junction (MREJ) region among 907 methicillin-resistant S. aureus(MRSA) and 900 methicillin-susceptible S. aureus(MSSA) isolates. The rate of mecA/mecCdropout mutants was also evaluated. Only three MRSA isolates (99.7% sensitivity; 904/907) were classified as MSSA by the BD Max StaphSR assay, due to negative results for MREJ. Eight MSSA isolates (99.1% sensitivity; 892/900) were assigned as MRSA. However, six of these MSSA isolates had the mecAgene confirmed by PCR and sequencing (99.8% sensitivity; 898/900). Overall, 7.1% (64/900) of MSSA isolates showed results compatible with a mecAdropout genotype.

ABSTRACTIsavuconazole is a new broad-spectrum triazole with a favorable pharmacokinetic and safety profile. We report the MIC distributions for isavuconazole and 111 isolates of Candida(42 Candida albicans, 25 Candida glabrata, 22 Candida parapsilosis, 14 Candida tropicalis, and 8 Candida kruseiisolates), as determined by Clinical and Laboratory Standards Institute (CLSI) and European Committee on Antimicrobial Susceptibility Testing (EUCAST) broth microdilution (BMD) methods. Also, the relative activities of isavuconazole, itraconazole, fluconazole, posaconazole, voriconazole, and the three echinocandins were assessed against a recent (2011) global collection of 1,358 isolates of Candidaspp., 101 of Aspergillusspp., 54 of non-Candidayeasts, and 21 of non-Aspergillusmolds using CLSI BMD methods. The overall essential agreement (EA) (±2 log2dilutions) between the CLSI and EUCAST methods was 99.1% (EA at ±1 log2dilution, 90.1% [range, 80.0 to 100.0%]). The activities of isavuconazole against the larger collection of Candidaspp. and Aspergillusspp. were comparable to those of posaconazole and voriconazole; the MIC90values for isavuconazole, posaconazole, and voriconazole against Candidaspp. were 0.5, 1, and 0.25 µg/ml and against Aspergillusspp. were 2, 1, and 1 µg/ml, respectively. Isavuconazole showed good activities against Cryptococcus neoformans(MIC90, 0.12 µg/ml) and other non-Candidayeasts (MIC90, 1 µg/ml) but was less potent against non-Aspergillusmolds (MIC90, >8 µg/ml). Isavuconazole MIC values for three mucormycete isolates were 4, 1, and 2 µg/ml, whereas all three were inhibited by 1 µg/ml posaconazole. Isavuconazole demonstrates broad-spectrum activity against this global collection of opportunistic fungi, and the CLSI and EUCAST methods can be used to test this agent against Candida, with highly comparable results.

ABSTRACTTedizolid, a novel oxazolidinone antibacterial with potent activity against a wide range of Gram-positive pathogens, was recently approved by regulatory authorities for the treatment of acute bacterial skin and skin structure infections. A commercial broth microdilution device (Sensititre; Thermo Fisher Scientific) was validated using 285 selected Gram-positive isolates, and the device was documented to have 100.0% essential and categorical agreement with reference MIC results and excellent MIC endpoint reproducibility.

We assessed the ceftazidime-avibactam disk diffusion breakpoints that provide the lowest discrepancy error rates by testing an Enterobacteralesisolate collection with ceftazidime-avibactam MIC values near the breakpoints. Isolates (n?=?112) were susceptibility tested by broth microdilution and disk diffusion methods in 3 laboratories. Current disk diffusion breakpoints (=21/=20?mm for susceptible/resistant) provided the lowest error rates, but confirmatory MIC testing is indicated for isolates with inhibition zones of 20 to 22?mm.

ABSTRACTWe evaluated the correlation between MIC and disk diffusion inhibition zones when testing ceftazidime-avibactam, using the 30/20-µg disk and the disk diffusion and MIC breakpoints established by the U.S. FDA and the Clinical and Laboratory Standards Institute (CLSI). Organisms used included 2 groups of Enterobacteriaceaeisolates and 2 groups of Pseudomonas aeruginosaisolates; 1 group of each consisted of randomly selected isolates and the second group consisted of a challenge group from thousands of surveillance isolates with an increased proportion of organisms displaying ceftazidime-avibactam MIC values close to the breakpoints. Broth microdilution, disk diffusion tests, and data analysis were performed according to reference standardized methods. Ceftazidime-avibactam breakpoints of =8/4 (susceptible) and =16/4 µg/ml (resistant) for MIC and =21/=20 mm for disk diffusion, as established by the U.S. FDA and the CLSI, were applied for Enterobacteriaceaeand P. aeruginosa. Ceftazidime-avibactam MIC and disk zone (30/20-µg disk) correlation were acceptable when testing Enterobacteriaceae(overall, very major [VM] and major [Ma] error rates of 0.4% and 0.0%, respectively) and nearly so when testing P. aeruginosa(2.3% VM and 2.9% Ma errors). In summary, disk diffusion and broth microdilution testing results demonstrated good categorical agreement for ceftazidime-avibactam against Enterobacteriaceaeand P. aeruginosa, using 30/20-µg disks.