title: Unique combined penA/mtrR/porB mutations and NG-MAST strain types associated with ceftriaxone and cefixime MIC increases in a 'susceptible' Neisseria gonorrhoeae population.
abstract: OBJECTIVE
  To determine which mutations in penA, mtrR and porB are implicated in increasing minimum MICs of ceftriaxone and cefixime in a susceptible gonococcal population and to ascertain associations with gonococcal strain types (STs).
  
  
  METHODS
  One hundred and forty-six Neisseria gonorrhoeae isolates formed two extended-spectrum cephalosporin susceptibility groups: group 1 isolates with cefixime and ceftriaxone MICs of 0.0005-0.016 mg/L; and group 2 isolates with cefixime MICs of 0.03-0.125 mg/L (n = 24) and ceftriaxone MICs of 0.03-0.06 mg/L (n = 23). Mutation patterns in penicillin-binding protein 2 (PBP2; penA), multiple transfer resistance repressor (MtrR; mtrR) and porin B (PorB; porB) were ascertained by DNA sequence and bioinformatic analysis. STs were determined using N. gonorrhoeae multiantigen sequence typing (NG-MAST).
  
  
  RESULTS
  Most isolates carried PBP2 mutation pattern IX (D345a, F504L, A510V, A516G and P551L; 50/146, 34.2%), a G45D substitution in MtrR (37.7%) and a wild-type (WT) sequence for PorB (43.2%). Group 2 gonococcal isolates were significantly associated with: penA pattern IX; dual mutations in the promoter (A-) and DNA dimerization domain (H105Y) of MtrR; and G120K;A121D substitutions in PorB. There were 50 combined penA/mtrR/porB mutation patterns, with corresponding patterns I/WT/WT and IX/G45D/G120K;A121D predominating. Gonococci susceptible to ceftriaxone and cefixime were significantly associated with NG-MAST ST 25 (33/36; 92%) and the combined penA/mtrR/porB mutation pattern I/WT/WT. No combined mutation pattern or specific ST was associated with elevated ceftriaxone MICs. NG-MAST ST 3654 was significantly associated with the pattern IX/G45D/G120K;A121D and cefixime group 2 isolates.
  
  
  CONCLUSIONS
  Specific single or combined mutation patterns in penA, mtrR and porB and specific STs were associated with differences in susceptibility to ceftriaxone and cefixime.
authors.affiliation: Department of Microbiology and Immunology, University of Saskatchewan, Saskatoon, SK, Canada.
authors.forename: S D
authors.initials: SD
authors.lastname: Thakur
authors.affiliation: Vaccine and Infectious Disease Organization-International Vaccine Centre, University of Saskatchewan, Saskatoon, SK, Canada.
authors.forename: S
authors.initials: S
authors.lastname: Starnino
authors.affiliation: Saskatchewan Disease Control Laboratory, Regina, SK, Canada.
authors.forename: G B
authors.initials: GB
authors.lastname: Horsman
authors.affiliation: Saskatchewan Disease Control Laboratory, Regina, SK, Canada.
authors.forename: P N
authors.initials: PN
authors.lastname: Levett
authors.affiliation: Department of Microbiology and Immunology, University of Saskatchewan, Saskatoon, SK, Canada Vaccine and Infectious Disease Organization-International Vaccine Centre, University of Saskatchewan, Saskatoon, SK, Canada j.dillon@usask.ca.
authors.forename: J R
authors.initials: JR
authors.lastname: Dillon
mesh_terms: D019943:Amino Acid Substitution; D001426:Bacterial Proteins / Q000235:genetics*; D002170:Canada; D020682:Cefixime / Q000494:pharmacology*; D002443:Ceftriaxone / Q000494:pharmacology*; D024881:Drug Resistance, Bacterial / Q000235:genetics*; D005260:Female; D006069:Gonorrhea / Q000382:microbiology*; D006801:Humans; D008297:Male; D008826:Microbial Sensitivity Tests; D009154:Mutation; D009344:Neisseria gonorrhoeae / Q000187:drug effects* / Q000235:genetics*
chemical_list: D001426:Bacterial Proteins; D002443:Ceftriaxone; D020682:Cefixime
keywords: antimicrobial resistance mechanisms; extended-spectrum cephalosporins; gonorrhoea