Study on the Plasmid and Chromosome-Determined Resistance to Penicillin and Tetracycline in Neisseria gonorrhoeae

Objective To investigate the in vitro antibiotic susceptibility and resistant trends of Neisseria gonorrhoeae strains isolated in Guangzhou from 2000 to 2005. Methods The agar dilution method was used to determine the resistance of N. gonorrhoeae to penicillin and tetracycline plasmid-mediated resistant strains. The penicillinase-producing N. gonorrhoeae(PPNG) was determined by paper acidometric method. Results A total of 631 N. gonorrhoeae isolates were examined. There were 132(20.9%) strains of PPNG and 222(35.2%) strains of plasmid mediated resistance to tetracycline (TRNG). During the period of 2000-2005, the prevalence of PPNG increased from 17.1% to 23.7%(χ2=0.955,P0.05 ), while TRNG significantly increased from 20% to 46.1% (χ2=11.94,P0.05). Positive rate of chromosome mediated resistance to penicillin increased from 76% to 98.3% (χ2=12.94, P0.05) and tetracycline ranged from 70.7% to 85.7% (χ2=3.246,P 0.05). During 2000-2005, MIC50 and MIC90 of penicillin changed from 1 mg/L and 2 mg/L to 4 mg/L and 32 mg/L, while MIC50 and MIC90 of tetracycline changed from 1 mg/L and 2 mg/L to 2 mg/L and 4 mg/L. Their MIC50 and MIC90 were significantly higher than resistant standards. Conclusion In the past 6 years, the prevalence of PPNG and TRNG had increased rapidly, and the proportions of chromosome mediated resistant isolates to penicillin and tetracycline were high in Guangzhou.