Decreased Susceptibility to Ceftriaxone in Neisseria Gonorrhoeae in the Absence of a Mosaic Penicillin-Binding Protein 2 (PenA) Allele

Background: In February, 2012, a 32 year old African American, heterosexual man in Oklahoma presented with gonorrhea exhibiting reduced susceptibility to ceftriaxone, with a minimum inhibitory concentration (MIC) of 0.5 µg/ml.  No history of travel, drug use, or sex work was reported, and the individual denied having prior gonococcal infections.   

Methods: Whole genome sequencing of this isolate was performed using next-generation sequencing techniques (Roche 454 and Pacific Biosciences SMRT), and a suite of known gonococcal resistance determinants were examined to identify mutations potentially associated with reduced susceptibility to ceftriaxone.

Results: The penicillin-binding protein 2 gene (penA) has been associated with both reduced susceptibility and treatment failure to the cephalosporins due to the presence of a mosaic penA allele; however, this particular isolate possessed a non-mosaic  penA allele not normally associated with decreased susceptibility to cephalosporins.

Conclusions: These results suggest that while a mosaic penA allele can be predictive for reduced susceptibility to cephalosporins in N. gonorrhoeae, it is not absolutely necessary.  In this case, it appears that other mutations are responsible for the reduced susceptibility to ceftriaxone.