Reconsidering azithromycin disc diffusion interpretive criteria for Salmonellae in view of azithromycin MIC creep among typhoidal and nontyphoidal salmonella

Abstract PURPOSE : Enteric fever continues to be an important public health challenge for the developing world. With the emergence of fluoroquinolone resistance in Salmonellae spp. azithromycin is increasingly being used for oral treatment of enteric fever. We investigated the antibiotic susceptibility pattern of azithromycin in Salmonellae spp. isolates from a tertiary care hospital to detect emerging resistance. METHODS : The study assessed the reliability of disc diffusion as a screening test to detect azithromycin resistance by comparing it with the minimum inhibitory concentrations (MICs) of the drug in 100 Salmonellae spp. strains. The strains of Salmonellae spp. showing resistance to azithromycin were further investigated for resistance markers – mphA, mphB, and mef B genes. RESULTS : This study was conducted on 100 Salmonella enterica strains recovered from blood culture samples between 2013 and 2017. Among these isolates, 18 showed resistance to azithromycin by disc diffusion methodology with zones of inhibition