Real-time PCR detection of Neisseria gonorrhoeae susceptibility to penicillin

Objectives: The objective of this study was to developa real-time PCR assay targeting the gonococcal porB gene (PorB-PCR) forpredicting susceptibility of Neisseria gonorrhoeae to penicillin. Thiscomplements a previously described PCR assay for detectingpenicillinase-producing N. gonorrhoeae (PPNG) developed by our laboratory(PPNG-PCR). 

Methods: The PorB-PCR assay was designed using sixprobes to characterize various combinations of amino acids at positions 101 and102 of the PorB1b class protein, including the WT G101/A102 and mutantG101K/A102D, G101K/A102N and G101K/A102G sequences, as well as the PorB1asequence. The ability of these sequences to predict penicillin susceptibilitywas initially assessed using 2307 N. gonorrhoeae isolates from throughoutAustralia for which phenotypic susceptibility data were available. The assaywas then applied to N. gonorrhoeae-positive clinical specimens (n = 70). Specificitywas assessed by testing commensal Neisseria strains (n = 75) and N.gonorrhoeae-negative clinical specimens (n = 171). 

Results: Testing of the 2307 N. gonorrhoeae isolatesusing PorB-PCR to detect G101/A102 and PorB1a sequences identified a total of78.4% (61.2% and 17.2%, respectively) of penicillin-susceptible isolates withspecificities of 97.4% and 99.3% and positive predictive values of 98.8% and98.9%, where PPNG strains were simultaneously identified and excluded. Similarperformance data were obtained when the PorB-PCR assay was applied to the N.gonorrhoeae-positive clinical specimens. No false-positive results wereobserved for the N. gonorrhoeae-negative samples and no cross-reactions wereobserved with the non-gonococcal species. 

Conclusions: When used in parallel with the previouslydescribed PPNG-PCR, the PorB-PCR approach has the potential to facilitateindividualized treatment of gonorrhoea using penicillin.