Spectinomycin

Tested compounds (i.e. 8HQ and derivatives) and antibiotics are comercially available. 8-Hydroxyquinoline (8HQ, 1); 5-chloro-8-Hydroxyquinoline (5-Cl-8HQ or cloxyquin, 2); 5-nitro-8-Hydroxyquinoline (5-NO₂-8HQ or nitroxoline, 3); 7-bromo-8-Hydroxyquinoline (7-Br-8HQ, 4); 5,7-diiodo-8-Hydroxyquinoline (5,7-diI-8HQ or iodoquinol, 5) and 5-chloro-7-iodo-8-hydroxy- quinoline (5-Cl-7-I-8HQ or clioquinol, 6) were obtained from Sigma-Aldrich. 5,7-Dichloro-8-Hydroxyquinoline (5,7-diCl-8HQ, 7) was purchased from Acros Organics. Spectinomycin was supplied with Bio Basic Inc. Chemical structures of the tested compounds are shown in Figure 1(Fig. 1).

The MIC was determined by an agar dilution method according to guidelines of the Clinical and Laboratory Standards Institute (2014[12 ]). Antimicrobial agents used in this study include penicillin G (Bio Basic Inc.), cefixime (Fluka), ceftriaxone (Sigma), ciprofloxacin (Fluka), tetracycline (Bio Basic Inc.), azithromycin (Fluka) and spectinomycin (Bio Basic Inc.) Each isolate was tested on a GC agar supplemented with 1 % of defined growth supplement containing 2-fold-increasing concentrations of antimicrobial agents. Plates were incubated in 5 % CO₂ at 37 °C for 24 h followed by recording the antimicrobial susceptibility results. The production of β-lactamase enzyme was detected using nitrocefin discs. N. gonorrhoeae strain ATCC 49226 was used as a control. The criteria of reduced susceptible to cefixime and ceftriaxone is according to the WHO document (WHO, 2012[65 ]) where N. gonorrhoeae strains displaying reduced susceptibility to cefixime exhibit MICs of ≥ 0.25 μg/ml and N. gonorrhoeae strain displaying reduced susceptibility to ceftriaxone yield MICs of ≥ 0.125 μg/ ml.