Background: We assessed the validity of testing for antimicrobial susceptibility of clinical and mutant Neisseria\ngonorrhoeae (GC) isolates by disk diffusion in comparison to agar dilution, and Etest�® (bioMerieux, France),\nrespectively, for three third generation extended spectrum cephalosporins (ESC): ceftriaxone (CRO), cefixime (CFX),\nand cefpodoxime (CPD).\nMethods: One hundred and five clinical isolates and ten laboratory-mutants were tested following Clinical\nLaboratory Standard Institute (CLSI) and manufacturerâ��s standards for each of the three methods. The measured\ndiameters by the disk diffusion method were tested for correlation with the MIC values by agar dilution. In addition,\ncomparisons with the Etest�® were made. Categorical results for concordance, based on standard CLSI cutoffs,\nbetween the disk diffusion and the other two methods, respectively, were tested using the Chi-square statistics.\nReproducibility was tested for CFX across a 6-month interval by repeated disk tests.\nResults: Across all 115 specimens, the disk diffusion tests produced good categorical agreements, exhibiting\nconcordance of 93.1%, 92.1%, and 90.4% with agar dilution and 93.0%, 92.1%, and 90.4% with Etest�®, for CRO, CFX,\nand CPD, respectively. Pearson correlations between disk-diffusion diameters and agar dilution MICâ��s were -0.59, -0.\n67, and -0.81 for CRO, CFX, and CPD, respectively. The correlations between disk diffusion and Etest�® were -0.58, -0.\n73, and -0.49. Pearson correlation between the CFX disk readings over a 6-month interval was 91%.\nConclusions: Disk diffusion tests remain to be a useful, reliable and fast screening method for qualitative\nantimicrobial susceptibility testing for ceftriaxone, cefixime, and cefpodoxime.
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