UCLA researchers in the David Geffen School of Medicine have developed a novel method to detect the susceptibility of Neisseria gonorrhoeae to the antibiotic cefixime.
Neisseria (N.) gonorrhoeae, is the world’s second most prevalent sexually transmitted bacterial infection. However, Neisseria Gonorrhoeae are naturally competent organisms that can acquire genetic material from the environment and mutate to become resistant to antibiotics. Cefixime, a third-generation oral cephalosporin, is a highly effective single dose treatment for gonorrhoea. In the last two decades, gonococcal strains with decreased susceptibility to cefixime and cases of clinical treatment failure with cefixime have been reported worldwide. The primary mechanism of N. gonorrhoeae resistance to extended-spectrum cephalosporins (ESCs) is alteration of the penA gene, which encodes the penicillin-binding protein 2 (PBP2), resulting in reduced affinity for ESCs. As a key determinant of susceptibility and resistance to ESCs, the penA gene is of particular interest for the development of rapid molecular assays. The lack of reliable molecular tests of ESC-resistance have led to the administration of a 2-drug combination that includes an injectable antibiotic. As the development of resistance against ESCs becomes an imminent threat, there is a great need for molecular tests that can accurately predict susceptibility to these agents. A rapid molecular screening test would provide information that would allow for real-time prediction of a samples’ minimum inhibitory concentration (MIC) to ESCs and administration of the appropriate antibiotic.
The invention identifies a novel combination of molecular point mutations in the penA gene for the penicillin binding protein-2 in N. gonorrhoeae that predict with > 98% reliability the susceptibility of N. gonorrhoeae infection to the antibiotic cefixime. The assay demonstrated high sensitivity (97%) and specificity (100%) for predicting whether ESC MICs were equal to or above the CDC alert values, in a panel of clinical isolates, while still maintaining the accuracy of prediction of ciprofloxacin susceptibility among clinical isolates tested when multiplexed with gyrA real-time PCR assay. Use of the assay would enable clinicians to treat patients with a simple oral appropriate medication leading to deceleration of the emergence of resistance, a major public health problem.
The target mutations have been identified, the PCR assay developed and tested in clinical samples.
cefixime, antibiotic resistance, molecular assay, PCR, extended-spectrum cephalosporins, gonorrhea, diagnosis