Abera Abdeta - National Clinical Bacteriology and Mycology Reference Laboratory, Ethiopian Public Health Institute, Addis Ababa, Ethiopia
Adane Bitew - Department of Medical Laboratory Sciences, College of Health Sciences, Addis Ababa University, Addis Ababa, Ethiopia
Surafel Fentaw - National Clinical Bacteriology and Mycology Reference Laboratory, Ethiopian Public Health Institute, Addis Ababa, Ethiopia
Estifanos Tsige - National Clinical Bacteriology and Mycology Reference Laboratory, Ethiopian Public Health Institute, Addis Ababa, Ethiopia
Dawit Assefa - National Clinical Bacteriology and Mycology Reference Laboratory, Ethiopian Public Health Institute, Addis Ababa, Ethiopia
Eyasu Tigabu - Global One Health Initiative, The Ohio State University, East African Regional Office, Addis Ababa, Ethiopia

Background: Early detection of extended-spectrum β-lactamases (ESBLs) producing bacteria is criticalfor infection prevention and control. Numerous phenotypic approaches and automated systems havebeen developed for detecting ESBL bacteria. However, there is a scarcity of data in Ethiopia regardingthe most reliable, simple, and cost-effective methods for detecting ESBL-producing bacteria. This study,therefore, aimed to evaluate the diagnostic performance of three phenotypic approaches for detectingESBL-producing bacteria.Methods: In this study, ۱۱۷ isolates of Klebsiella pneumoniae, Escherichia coli, Klebsiella oxytoca, andProteus mirabilis were examined. Cefotaxime (۳۰ μg) and ceftazidime (۳۰ μg) were used for screeningESBL enzymes. A screening breakpoints of ≤ ۲۷ mm and ≤ ۲۲ mm were used for cefotaxime (۳۰ μg) andceftazidime (۳۰ μg), respectively, as per the Clinical and Laboratory Standards Institute (CLSI) guidelines.All ۱۱۷ strains were further confirmed by the Vitek ۲ compact, double disk synergy, ESBL Epsilometer test,and combined disk method. The combined disk method was adopted as the reference method.Results: Out of ۱۱۷ isolates, ۹۰ (۸۶%) had zone diameters of ≤ ۲۷ mm and ≤ ۲۲ mm for cefotaxime (۳۰ μg)and ceftazidime (۳۰ μg), respectively. The reference method detected ۷۶ (۶۵%) ESBL isolates out of ۱۱۷ones. From among the three techniques (i.e., double disk synergy, Vitek ۲ compact, and ESBL Epsilometertest), the double disk synergy method demonstrated overall sensitivity and specificity of ۹۷.۴% and ۹۷.۶%,respectively. Vitek-۲, cefotaxime, and ceftazidime Epsilometer test indicated indeterminate results of ۶.۸%,۶.۸%, and ۵.۱% respectively.Conclusion: Double disk synergy was found to have the highest sensitivity and specificity for detectingESBL isolates with no indeterminate results.

Double disk synergy, Combined disk, Gradient strip, Vitek ۲ compact