The Diagnostic Capacity of Three Phenotypic Techniques of Extended-Spectrum β-Lactamase Detection

Background: Early detection of extended-spectrum β-lactamases (ESBLs) producing bacteria is critical for infection prevention and control. Numerous phenotypic approaches and automated systems have been developed for detecting ESBL bacteria. However, there is a scarcity of data in Ethiopia regarding the 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 detecting ESBL-producing bacteria. Methods: In this study, 117 isolates of Klebsiella pneumoniae, Escherichia coli, Klebsiella oxytoca, and Proteus mirabilis were examined. Cefotaxime (30 µg) and ceftazidime (30 µg) were used for screening ESBL enzymes. A screening breakpoints of≤27 mm and≤22 mm were used for cefotaxime (30 µg) and ceftazidime (30 µg), respectively, as per the Clinical and Laboratory Standards Institute (CLSI) guidelines. All 117 strains were further confirmed by the Vitek 2 compact, double disk synergy, ESBL Epsilometer test, and combined disk method. The combined disk method was adopted as the reference method. Results: Out of 117 isolates, 90 (86%) had zone diameters of≤27 mm and≤22 mm for cefotaxime (30 µg) and ceftazidime (30 µg), respectively. The reference method detected 76 (65%) ESBL isolates out of 117 ones. From among the three techniques (i.e., double disk synergy, Vitek 2 compact, and ESBL Epsilometer test), the double disk synergy method demonstrated overall sensitivity and specificity of 97.4% and 97.6%, respectively. Vitek-2, cefotaxime, and ceftazidime Epsilometer test indicated indeterminate results of 6.8%, 6.8%, and 5.1% respectively. Conclusion: Double disk synergy was found to have the highest sensitivity and specificity for detecting ESBL isolates with no indeterminate results.