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


METHODS
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.


RESULTS
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).


CONCLUSIONS
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.
Whiley
David M
DM
Queensland Paediatric Infectious Diseases Laboratory, Queensland Children's Medical Research Institute, Children's Health Service District, Queensland, Australia. d.whiley@uq.edu.au
Goire
Namraj
N
Lambert
Stephen B
SB
Ray
Sanghamitra
S
Limnios
E Athena
EA
Nissen
Michael D
MD
Sloots
Theo P
TP
Tapsall
John W
JW
D019943:Amino Acid Substitution / Q000235:genetics; D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D001426:Bacterial Proteins / Q000235:genetics*; D002443:Ceftriaxone / Q000494:pharmacology*; D008826:Microbial Sensitivity Tests; D020125:Mutation, Missense; D009344:Neisseria gonorrhoeae / Q000187:drug effects*; D046915:Penicillin-Binding Proteins / Q000235:genetics*; D017422:Sequence Analysis, DNA; D018440:beta-Lactam Resistance
D000900:Anti-Bacterial Agents; D001426:Bacterial Proteins; D046915:Penicillin-Binding Proteins; D002443:Ceftriaxone