Antimicrobial Resistance Profile and Molecular Screening for the penA-60.001 Allele in Neisseria gonorrhoeae Detected in Zagreb County, Croatia

The rise in antimicrobial-resistant Neisseria gonorrhoeae (NG) strains poses major challenges to gonorrhea treatment worldwide. Ceftriaxone remains the first-line antibiotic therapy; however, emerging resistance, particularly driven by the mosaic penA 60.001 allele, necessitates vigilant surveillance. This study assesses the antimicrobial susceptibility patterns of NG isolates in the northwestern region of Croatia and evaluates the correlation between phenotypic susceptibility testing for extended-spectrum cephalosporins (ESC) and genotypic detection of the penA 60.001 allele. A total of 39 clinical NG-positive specimens by a multiplex PCR panel for urogenital infections were collected between 1 July 2022, and 30 June 2024. Phenotypic antimicrobial susceptibility testing was performed using the Etest method. Genotypic detection of ceftriaxone resistance determinants was performed using a multiplex nested PCR assay. All NG isolates were susceptible to ceftriaxone and cefixime. High resistance rates were observed for ciprofloxacin (70.6%), tetracycline (44.1%), and azithromycin (20.6%). Mutations in the penA gene associated with decreased susceptibility to ceftriaxone were detected in three samples, although phenotypic resistance was not observed. The high resistance rates to ciprofloxacin, tetracycline, and azithromycin limit their use for empirical therapy in Croatia. While ceftriaxone remains effective, the detection of penA mutations highlights the need for ongoing surveillance.