Ceftibuten resistance and treatment failure of Neisseria gonorrhoeae infection

Neisseria gonorrhoeae infections have been empirically treated in Hong Kong with a single oral 400-mg dose of ceftibuten since 1997. Following anecdotal reports of the treatment failure of gonorrhea with oral extended-spectrum cephalosporins, the current study was undertaken to determine the antimicrobial susceptibility pattern and molecular characteristics of isolates of N. gonorrhoeae among patients with putative treatment failure in a sexually transmitted disease clinic setting. Between October 2006 and August 2007, 44 isolates of N. gonorrhoeae were studied from patients identified clinically to have treatment failure with empirical ceftibuten. The ceftibuten MICs for three strains were found to have been 8 mg/liter. These strains were determined by N. gonorrhoeae multiantigen sequence typing to belong to sequence type 835 (ST835) or the closely related ST2469. The testing of an additional eight archived ST835 strains revealed similarly elevated ceftibuten MICs. The penA gene sequences of these 11 isolates all had the mosaic pattern previously described as pattern X. Of note is that the ceftriaxone susceptibility results of these strains all fell within the susceptible range. It is concluded that ceftibuten resistance may contribute to the empirical treatment failure of gonorrhea caused by strains harboring the mosaic penA gene, which confers reduced susceptibility to oral extended-spectrum cephalosporins. Screening for such resistance in the routine clinical laboratory may be undertaken by the disk diffusion test. The continued monitoring of antimicrobial resistance and molecular characteristics of N. gonorrhoeae isolates is important to ensure that control and prevention strategies remain effective.