EVALUATION OF INTERPRETIVE CRITERIA OF AGAR DILUTION AND DISK DIFFUSION SUSCEPTIBILITY TESTS FOR NEISSERIA-GONORRHOEAE

Using strains of Neisseria gonorrhoeae from Western New York, the Nati onal Committee for Clinical Laboratory Standards' (NCCLS) interpretive criteria for disk diffusion susceptibility testing was evaluated on c hocolate-Mueller-Hinton agar (CMH) and GC agar. The reference method f or comparison was the NCCLS agar dilution minimum inhibitory concentra tion (MIC) method. Even though the zone sizes were significantly small er on the CMH agar, the interpretations were not significantly differe nt on either GC or CMH agars except for tetracycline. On the GMH agar, the number of tetracycline-resistant strains was greater than on GC a gar: 3% of the strains failed to grow on CMH agar and 4% did not produ ce interpretable zone sizes for ceftriaxone. Therefore, the use of CMH is not recommended. There was a significant difference between the in terpretative criteria of the MIC and the disk diffusion method only fo r tetracycline. Therefore, the NCCLS zone-diameter interpretation crit eria for tetracycline does not seem applicable for N. gonorrhoeae isol ates in the Buffalo, New York, area.