Investigation of the azithromycin resistance rate and related genes involved in this resistance in clinical Shigella species collected from children with diarrhea in Ahvaz, Southwest Iran.

BACKGROUND: This study aimed to investigate the azithromycin resistance rate and the related genes in clinical Shigella species obtained from children with diarrhea in Ahvaz, southwest Iran. METHODS AND RESULTS: Shigella isolates were collected from children with diarrhea and identified using biochemical tests and polyvalent antisera. Antibiotic susceptibility testing was performed using disk diffusion. Minimum inhibitory concentrations (MICs) of azithromycin were determined by the agar dilution method in the presence and absence of efflux inhibitor, phenylalanine-arginine β-naphthylamide (PAβN) (20 µg/ml). The presence of macrolide-associated resistance genes was investigated by polymerase chain reaction. In total, 126 Shigella isolates, including S. sonnei (61.11%, n = 77), S. flexneri (34.92%, n = 44), and S. boydii (3.97%, n = 5) were detected. High resistance rates to nalidixic acid (99.20%), ampicillin (91.27%), cefazolin (84.13%), and trimethoprim-sulfamethoxazole (73.01%) were found among the Shigella isolates, with 77.0% classified as multidrug-resistant (MDR) (non-susceptibility to at least 1 antibiotic in ≥ 3 and < 6 antimicrobial categories) and 17.46% as extensively drug-resistant (XDR) (non-susceptibility to at least 1 antibiotic in ≥ 6 antimicrobial categories). Based on MICs results, 67.46% (n = 85) of isolates were azithromycin-resistant. In 8 (9.41%) azithromycin-resistant isolates, MICs were reduced in the presence of PAβN. Prevalence of mphA and ermB genes among azithromycin-resistant isolates was 98.82% and 8.23%, respectively. A significant relationship between azithromycin resistance and the presence of the mphA gene was observed. CONCLUSIONS: This study highlighted a concerning level of azithromycin resistance that is a main challenge for the treatment of MDR Shigella species in the studied region. Furthermore, the presence of mphA and ermB genes are main mechanisms of azithromycin resistance in southwest of Iran. Further studies with focus on other resistance mechanisms including efflux pump genes (ompA, ompW, various msr and mef) are needed.