Detection of carbapenemase genes and other resistance mechanisms in carbapenem-resistant/cephalosporin-susceptible Pseudomonas aeruginosa

Document Type : New and original researches in the field of Microbiology.

Authors

1 Medical Microbiology Department, AlAzhar Faculty of medicine, Cairo, Egypt

2 Medical Microbiology Laboratory Department, Alnoor Specialist Hospital, Holy Makkah, Saudi Arabia

3 Medical Microbiology Laboratory Department, Alnoor Specialist Hospital, Holy Makkah, Saudi Arabi

4 Medical Microbiology and Immunology Department, Faculty of medicine – Cairo University, Cairo, Egypt

Abstract

Background: Carbapenem- resistant P. aeruginosa isolates are increasingly observed. Carbapenem resistance in P. aeruginosa is modulated by acquired carbapenemases in association with non-carbapenemases mechanisms. An uncommon phenotype of carbapenem resistant but cephalosporine susceptible (Carb- R/ Ceph- S) Ps. aeruginosa clinical isolates have been reported. Objective: We aimed to assess mechanisms of carbapenem resistant in this characteristic uncommon phenotype. Methodology: A total of 168 carbapenem resistant clinical isolates of Ps. aeruginosa were recovered form admitted cases in a Tertiary Care Hospital during the period from November 2021 to October 2022. All Carb- R/ Ceph- S Pseudomonas aeruginosa isolates were subjected to the following to detect carbapenems resistant mechanism (s):  Genotypic discovery of carbapemenases production, phenotypic detection both of AmpC overproduction and efflux pumps overproduction. Results: 48 isolates (28.6%) were cephalosporine susceptible (Carb-R/ Ceph-S). Genotypic discovery of carbapenemases encoding genes by multiplex PCR and phenotypic detection of AmpC overproduction and efflux pumps overproduction were done to identify the possible mechanisms of carbapenem resistant in the studied phenotypes. None of 48 Carb- R/ Ceph-S P. aeruginosa isolates were carrying carbapenemases encoding genes, 60.4% (29/48) had efflux pumps overproduction and 4.2% (2/48) had AmpC overproduction. The highest rate of antimicrobial resistance was to Tigecycline and Colistin and the smallest rate of antimicrobial resistance was to Piperacillin/ Tazobactam, and Tobramycin and Amikacin. Conclusions: None of Carb-R/ Ceph-S P. aeruginosa harboring carbapenemases encoding genes, whereas;   efflux pumps overproduction and AmpC overproduction were detected in 60.4% and 4.2% respectively.

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