Roles of penA and mtrR gene mutations in in vitro-induced resistance of Neisseria gonorrhoeae to ceftriaxone

Abstract

Objective To investigate the roles of penA and mtrR gene mutations in resistance of Neisseria gonorrhoeae to ceftriaxone. Methods Standard strains of Neisseria gonorrhoeae (ATCC-49226) , clinical strains of Neisseria gonorrhoeae with high sensitivity to ceftriaxone (2012-4052 and 2012-15361) and clinical strains of Neisseria gonorrhoeae with reduced sensitivity to ceftriaxone (2012-5616) were treated with ceftriaxone at subinhibitory concentration (50% MIC) , so as to induce the resistance to ceftriaxone. DNA was extracted from the primary strains before the treatment and daughter strains resistant to ceftriaxone after the treatment, followed by the amplification and DNA sequencing of the penA and mtrR genes. Results For strains 2012-5616 and ATCC-49226, ceftriaxone-resistant strains with MIC ≥ 1 mg/L were obtained after 26 and 28 passages, respectively. For strains 2012-4052 and 2012-15361, ceftriaxone-resistant strains with MIC ≥ 0.5 mg/L were obtained after 22 and 36 passages, respectively. Sequence analysis of the penA gene revealed that A501T and G542S mutations were identified in the induced resistant ATCC-49226 strains, but no new mutations were observed in the other 3 strains. All the 4 mutant strains showed penicillin-binding protein 2 (PBP2) of gene sequence typeⅩⅧ, and no mosaic structure of the penA gene was found in the strains. Sequence analysis of the mtrR gene showed that the A39T mutation was found in the 2012-5616 and ATCC-49226 strains before and after the induction, as well as in the coding region of the mtrR gene in the induced resistant 2012-4052 strains. Conclusion The A501T and G542S mutations in the penA gene and A39T mutation in the mtrR gene may play a role in the resistance of Neisseria gonorrhoeae to ceftriaxone. Key words: Neisseria gonorrhoeae; Ceftriaxone; Beta-lactam resistance; penA gene; mtrR gene