Reduced susceptibility to ceftriaxone in Neisseria gonorrhoeae is associated with mutations G542S, P551S and P551L in the gonococcal penicillin-binding protein 2

Reduced susceptibility to extended-spectrum cephalosporins in Neisseria gonorrhoeae has, to date, been associated with three alterations: a mosaic penA allele encoding the penicillin-binding protein 2 (PBP2); A-del-mtrR, an adenine deletion in the mtrR promoter; and penB, comprising mutated alleles of PorBIb. In this study, we examined an association between reduced susceptibility to ceftriaxone and additional mutations in gonococcal PBP2. N. gonorrhoeae isolates (n = 76) exhibiting reduced susceptibility to ceftriaxone but lacking the mosaic penA sequence were investigated for A-del-mtrR and penB as well as substitutions at PBP2 501, 542 and 551 using a previously described real-time PCR approach. To further investigate PBP2 542 and 551 substitutions, we reanalysed penA sequence data from a previous study of 98 gonococci exhibiting a range of ceftriaxone MICs. Of 76 N. gonorrhoeae isolates exhibiting reduced susceptibility to ceftriaxone and lacking the mosaic penA sequence, a 501 (A501V or A501T) substitution was present in 9/76, a 542 substitution in 39/76 and a 551 substitution in 26/76 isolates. Reanalysis of 98 gonococcal isolates from a previous study showed that substitutions at PBP2 542 (G542S) and 551 (P551S or P551L) were significantly associated with raised MICs to ceftriaxone (P = 0.0186 and 0.001, respectively) and penicillin (P = 0.0231 and 0.0007, respectively). Our findings provide strong evidence for the involvement of PBP2 G542S and P551S/P551L in reduced susceptibility to ceftriaxone and to penicillin. Further studies are needed to investigate the precise and relative roles played by these mutations.