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This study aimed to evaluate the minimum inhibitory concentration (MIC) of azithromycin (AZM) in clinical isolates of extensively drug-resistant (XDR) Salmonella Typhi (i.e., resistant to chloramphenicol, ampicillin, trimethoprim-sulfamethoxazole, fluoroquinolones, and third-generation cephalosporin) using the E-test versus the broth microdilution method (BMD). From January to June 2021, a retrospective cross-sectional study was carried out in Lahore, Pakistan. Antimicrobial susceptibility was performed initially by the Kirby-Bauer disk diffusion method for 150 XDR Salmonella enterica serovar Typhi isolates, and MICs of all the recommended antibiotics were determined by the VITEK 2 (BioMérieux) fully automated system using Clinical Laboratory Standard Institute (CLSI) 2021 guidelines. The E-test method was used to determine AZM MICs. These MICs were compared with the BMD, which is the method recommended by the CLSI but not adopted in routine laboratory reporting. Of 150 isolates, 10 (6.6%) were resistant by disk diffusion. Eight (5.3%) of these had high MICs against AZM by the E-test. Only three isolates (2%) were resistant by E-test, having an MIC of 32 μg/mL. All eight isolates had a high MIC by BMD with different MIC distributions, but only one was resistant, having an MIC of 32 μg/mL by BMD. The sensitivity, specificity, negative predictive value, positive predictive value, and diagnostic accuracy of the E-test method versus BMD were 98.65%,100%, 99.3%, 33.3%, and 98.6%, respectively. Similarly, the concordance rate was 98.6%, negative percent agreement was 100%, and positive percent agreement was 33%. The BMD is the most reliable approach for reporting AZM sensitivity in XDR S. Typhi compared with the E-test and disk diffusion methods. Potentially, AZM resistance in XDR S. Typhi is around the corner. Sensitivity patterns should be reported with MIC values, and if possible, higher values should be screened for the presence of any potential resistance genes. Antibiotic stewardship should be strictly implemented.
The datasets used and/or analyzed during the current study are not publicly available because the study was completely anonymous. This study was conducted using the bacterial strains that were isolated for diagnostic and treatment purposes. However, they are available from the corresponding author upon reasonable request.
Authors’ addresses: Kokab Jabeen, Sidrah Saleem, Faiqa Arshad, and Shah Jahan, University of Health Sciences, Lahore, Pakistan, E-mails: firstname.lastname@example.org, email@example.com, firstname.lastname@example.org, and email@example.com. Summiya Nizamuddin, Shaukat Khanum Memorial Cancer Hospital, Lahore, Pakistan, E-mail: firstname.lastname@example.org. Faisal Hasnain, Sheikh Zayed Hospital, Rahim Yar Khan, Pakistan, E-mail: email@example.com. Waleed Tariq, Lahore General Hospital, Lahore, Pakistan, E-mail: firstname.lastname@example.org. Muhammad Junaid Tahir, Pakistan Kidney and Liver Institute and Research Center (PKLI & RC), Lahore, Pakistan, E-mail: email@example.com. Zohaib Yousaf, Tower Health, Reading, PA, E-mail: firstname.lastname@example.org. Muhammad Sohaib Asghar, Dow University of Health Sciences, Karachi, Pakistan, E-mail: email@example.com.