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.
Queensland Paediatric Infectious Diseases Laboratory, Queensland Children's Medical Research Institute, Children's Health Service District, Queensland, Australia. d.whiley@uq.edu.au
David M
DM
Whiley
Namraj
N
Goire
Stephen B
SB
Lambert
Sanghamitra
S
Ray
E Athena
EA
Limnios
Michael D
MD
Nissen
Theo P
TP
Sloots
John W
JW
Tapsall
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