Various phenotypic techniques for detection of beta-lactam resistance in Pseudomonas species and Acinetobacter species: a single-center experience

Background The World Health Organization has emphasized that the risk of antibiotic resistance of Pseudomonas aeruginosa (PSA) and Acinetobacter baumannii (ACB) is due to the extended-spectrum β-lactamase (ESBL) and carbapenemase activity. Objectives The study was designed to describe the rates of different β-lactamases, and to assess the best phenotypic method for detection of these resistances. Methodology This cross-sectional study included 124 isolates obtained from the patients of Assiut University Hospital. Screening and phenotypic confirmatory tests for resistance were done. The study was approved and monitored by the Medical Ethics Committee, Assiut Faculty of Medicine, IRB 17101464. The antimicrobial-susceptibility tests were done by the Kirby–Bauer disk-diffusion method according to the CLSI 2019 guidelines and by automated Vitek2 Compact 15 system. Also, different phenotypic methods were used. Results The highest percentages of β-lactamase enzymes in 52 Pseudomonas isolates (53.8%) were due to both ESBL and carbapenemases (CARBA), whereas isolates with solo ESBL were 19.2% of the total isolates and the least percentages were due to CARBA. The highest percentages of β-lactamase enzymes in 72 Acinetobacter isolates (33.3%) were due to CARBA alone, whereas isolates with both ESBL and CARBA were 16.7% of the total isolates and the least percentages (5.6%) were due to ESBL. The combined-disk test had a high sensitivity and specificity in detection of ESBL and metallo-beta-lactamase (MBL) in PSA, whereas in ACB showed high sensitivity only. Conclusion The ESBL and MBL showed the highest percentage among Pseudomonas isolates, whereas among Acinetobacter isolates, the MBL showed the highest percentage. The phenotypic confirmatory tests showed high sensitivity and specificity and proved to be reliable approaches for identification of the β-lactamase resistance.