Novel Genes Related to Ceftriaxone Resistance Found among Ceftriaxone-Resistant Neisseria gonorrhoeae Strains Selected In Vitro

ABSTRACT The emergence of ceftriaxone-resistant Neisseria gonorrhoeae is currently a global public health concern. However, the mechanism of ceftriaxone resistance is not yet fully understood. To investigate the potential genes related to ceftriaxone resistance in Neisseria gonorrhoeae, we subcultured six gonococcal strains with increasing concentrations of ceftriaxone and isolated the strains that became resistant. After analyzing several frequently reported genes involved in ceftriaxone resistance, we found only a single mutation in penA (A501V). However, differential analysis of the genomes and transcriptomes between pre- and postselection strains revealed many other mutated genes as well as up- and downregulated genes. Transformation of the mutated penA gene into nonresistant strains increased the MIC between 2.0- and 5.3-fold, and transformation of mutated ftsX increased the MIC between 3.3- and 13.3-fold. Genes encoding the ABC transporters FarB, Tfq, Hfq, and ExbB were overexpressed, while pilM , pilN , and pilQ were downregulated. Furthermore, the resistant strain developed cross-resistance to penicillin and cefuroxime, had an increased biochemical metabolic rate, and presented fitness defects such as prolonged growth time and downregulated PilMNQ. In conclusion, antimicrobial pressure could result in the emergence of ceftriaxone resistance, and the evolution of resistance of Neisseria gonorrhoeae to ceftriaxone is a complicated process at both the pretranscriptional and posttranscriptional levels, involving several resistance mechanisms of increased efflux and decreased entry.