Neisseria gonorrhoeae isolates with reduced susceptibility to cefixime and ceftriaxone: association with genetic polymorphisms in penA, mtrR, porB1b, and ponA

Abstract

The recent emergence and transmission of Neisseria gonorrhoeae isolates with reduced susceptibility to expanded-spectrum cephalosporins such as cefixime and ceftriaxone have been reported. The aim of this study was to determine the correlation of different polymorphisms in the penA, mtrR, porB1b (penB), and ponA genes of N. gonorrhoeae with reduced susceptibility to cefixime and ceftriaxone. Eighteen gonococcal isolates with reduced cefixime and ceftriaxone susceptibility (Cef(i)) and two susceptible isolates were characterized using serovar determination, antibiograms, N. gonorrhoeae multiantigen sequence typing (NG-MAST), and sequencing of penA, mtrR, porB1b, and ponA alleles. For the Cef(i) isolates (n = 18), the MICs of cefixime and ceftriaxone ranged between 0.032 to 0.38 mug/ml and 0.064 to 0.125 mug/ml, respectively. These isolates were assigned five different serovars and six divergent NG-MAST sequence types. Eleven isolates (61%) with higher MICs of cefixime and ceftriaxone contained a nearly identical penA mosaic allele and previously described polymorphisms in mtrR (a single nucleotide [A] deletion in the promoter), penB (mutations in porB1b encoding loop 3 of PorB1b), and ponA (ponA1 polymorphism). The remaining seven Cef(i) isolates (39%), which had somewhat lower MICs of cefixime and ceftriaxone, contained an aspartic acid insertion (Asp-345a) in PBP 2 in conjunction with alterations of 4 to 10 amino acid residues in the C-terminal region of the transpeptidase domain of penA. In conclusion, an unambiguous association between penA mosaic alleles, in conjunction with genetic polymorphisms in mtrR, porB1b, and ponA, and greater reduced susceptibility to cefixime and ceftriaxone was identified.

FIG. 1.

Multiple-sequence alignment of the amino acid sequences of PBP 2 in Cefⁱ strains of N. gonorrhoeae. One representative of each distinct sequence variant associated with reduced susceptibility to cefixime and ceftriaxone in the present study is displayed (n = 8). Dots denote identity with the wild-type PBP 2 amino acid sequence of the N. gonorrhoeae strain LM306 (GenBank accession no. M32091), and dashes represent alignment gaps due to insertions/deletions. The mosaic PBP 2 sequence of the N. gonorrhoeae strain NG-3 (GenBank accession no. AB071984), which previously has been associated with reduced cefixime susceptibility (1), is also shown.