[Correlation between predominant pI genotypes, G120/A121 mutations and drug resistance]

To analyze the predominant genotypes of outer membrane porin I (PI) and to determine the correlation between G120 as well as A121 mutations in PI proteins and drug resistance in Neisseria gonorrhoeae isolates in the local area.

A double PCR to simultaneously detect both pIA and pIB genes, was established in this study. The target amplification products were T-A cloned and then sequenced to determine the mutations at G120, A121 and the specificity of double PCR. By using acidity slip method and double agar dilution method, the beta-lactamase production and resistance to six antibiotics of pIA(+) and pIB(+) gonococcal isolates were detected.

Double PCR could be used to accurately genotyping pI genes in all the tested gonococcal isolates with the sensitivity of 1 ng DNA template. In the 116 N. gonorrhoeae isolates, 30.2% (35/116) were pIA(+) strains and 69.8% (81/136) were pIB(+) strains. All the pIA(+) strains presented G120D/A121G double mutations (88.6%)or A121G single mutation (11.4%). 98.8% of the pIB(+) strains presented G120K/A121D (65.0%), G120K/A121G or G120N/A121D (13.8%) double mutations, and G120D/N/K single mutation (21.3%). 34.5% (40/116) of the isolates produced beta-lactamase, and the enzyme-produced rate (20%) in pIA(+) strains was significantly lower than that in pIB(+) strains (40.7%) with P < 0.05. No spectinomycin-resistant strains were identified but three ceftriaxone-resistant strains were presented. However, the resistance ratios to penicilin, tetramycin, ciprofloxacin and azithromycin of all the isolates were as high as 75.0% - 90.5%. 100% and 71.4% of the pIA(+) strains without beta-lactamase production and with G120 and/or A121 mutations were sensitive to penicillin and tetramycin, respectively. On the contrast, 100% of the pIB(+) strains without beta-lactamase production and with G120 and/or A121 mutations were resistant to both the two antibiotics.

The established double PCR method could be used for fast and accurate genotyping of N. gonorrhoeae pI genes. The N. gonorrhoeae strains prevalent in the local areas mainly possessed pIB gene. Both spectinomycin and ceftriaxone could still be chosen to treat gonorrhea. The resistance enhancement caused by G120 and/or A121 mutations to penicillin and tetramycin was only presented in pIB(+) gonococci.