Disc Diffusion Testing of Azithromycin Against Clinical Isolates of Typhoidal Salmonellae: A Diagnostic Conundrum

• Published in: Curēus (Palo Alto, CA) CA), 2021-07, Vol.13 (7), p.e16777-e16777
• Main Authors: Shoaib, Muhammad, Satti, Luqman, Hussain, Ashfaq, Khursheed, Nazia, Sarwar, Saba, Shah, Abid H
• Format: Article
• Language: English
• Subjects: Infectious Disease; Pathology
• ISSN: 2168-8184; 2168-8184
• DOI: 10.7759/cureus.16777

INTRODUCTION Typhoid remains a major healthcare problem in low and middle-income countries. The emergence of extremely drug-resistant (XDR) typhoid strains from the Indian subcontinent has led to very limited therapeutic options. Azithromycin being the only oral option for XDR typhoid faces a threat of rapid resistance due to its overuse after the COVID-19 pandemic. OBJECTIVE To evaluate the reliability of azithromycin disc diffusion testing against clinical isolates of typhoidal salmonellae in comparison with E-test minimum inhibitory concentrations (MICs). STUDY DESIGN This is a cross-sectional validation study. Place and duration of the study: The Department of Microbiology, Pakistan Navy Ship Shifa hospital, Karachi from June 1 to December 31, 2020. METHODOLOGY Antimicrobial susceptibility was performed by Kirby Bauer disc diffusion method for 60 isolates including Salmonella enterica ser. Typhi and Paratyphi A using Clinical Laboratory Standard Institute (CLSI) guidelines. MICs by the E-test method were determined for Azithromycin only. RESULTS A significant proportion of the isolates (55%) had high azithromycin MIC in the wild-type distribution range (8-16 µg/ml). Ten (16.6%) isolates showed false resistance, i.e., zone diameter