Abstract
BackgroundVariations of porB1A and porB1B genes and their serotypes exist in Neisseria gonorrhoeae isolates from different geographical areas, and some site mutations in the porB1B gene correlate with drug resistance.MethodsThe β-lactamase production of N. gonorrhoeae isolates was determined by paper acidometric test and nitrocefin discs. The porB1A and porB1B genes of 315 non-penicillinase-producting N. gonorrhoeae (non-PPNG) strains were amplified by PCR for sequencing to determine serotypes and site mutations. A duplex PCR was designed to simultaneously detect both porB1A and porB1B genes. Penicillin and tetracycline resistance was assessed by an in vitro drug sensitivity test.ResultsOf the N. gonorrhoeae isolates, 31.1% tested positive for porB1A and 68.9% for porB1B genes. All the 98 porB1A+ isolates belonging to IA6 serotype with either no mutation at the 120 and 121 sites (88.8%) or a D120G (11.2%) mutation and were no resistance to both penicillin and tetracycline. Among the 217 porB1B+ isolates, 26.7%, 22.6% and 11.5% belonged to IB3, IB3/6 and IB4 serotypes, respectively. Particularly, two novel chimeric serotypes, IB3/6-IB2 and IB2-IB4-IB2, were found in 77 and 8 porB1B+ isolates. Two hundred and twelve (97.7%) of the porB1B+ isolates were presented G120 and/or A121 mutations with 163 (76.9%) at both sites. Interestingly, within the 77 porB1B+ isolates belonging to IB3/6-IB2 serotype, 15 were discovered to possess novel deletions at both A121 and N122 sites. All the replacement mutations at these sites in PorB1B were correlated with resistance and the deletion mutation showed the highest resistance.ConclusionN. gonorrhoeae isolates circulating in Eastern China include a sole PorB1A serotype (IA6) and five PorB1B serotypes. Multiple mutations in porB1B genes, including novel A121 and N122 deletions, are correlated with high levels of penicillin and tetracycline resistance.
Highlights
Variations of porB1A and porB1B genes and their serotypes exist in Neisseria gonorrhoeae isolates from different geographical areas, and some site mutations in the porB1B gene correlate with drug resistance
Duplex polymerase chain reaction (PCR) The sequencing data of porB1A and porB1B genes from the N. gonorrhoeae isolates showed that these genes have over 80% identity at the 5’ terminal sequences (1-240 bp segments in both genes) and approximately 90% identity at the 3’ terminal sequences (714-981 bp segment in porB1A gene and 777-1044 bp segment in porB1B gene)
By using the duplex PCR, we found 31.1% of the 315 isolates tested were positive for the porB1A gene and the porB1B gene was detectable in 68.9% of the isolates
Summary
Variations of porB1A and porB1B genes and their serotypes exist in Neisseria gonorrhoeae isolates from different geographical areas, and some site mutations in the porB1B gene correlate with drug resistance. Determination of porB1A and porB1B genotype distribution in N. gonorrhoeae isolates in different areas is very important for providing a high index of discrimination of different gonococcal strains, identifying the circulating strains and predominant serotypes, and tracking strain transmission in sexual contacts [28,29,30,31,32]. Mutation at the 120 and 121 sites in PorB1B sequence from the non-penicillinase-producting N. gonorrhoeae (nonPPNG) isolates, as well as the correlation between the mutation patterns and the resistance to penicillin and tetracycline, were investigated
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