Role of integrons in dissemination of carbapenem resistance among pseudomonas aeruginosa and acinetobacter baumanii at Mulago Hospital

Abstract

Background: Carbapenem Resistance emergence threatens effective antimicrobial therapy of infections involving carbapenemase producing Gram negative bacteria especially Pseudomonas aeruginosa and Acinetobacter baumannii. This study aimed to determine the antimicrobial susceptibility profiles, prevalence of carbapenemase encoding genes, their location and class 1 integrons in carbapenem resistant Pseudomonas aeruginosa (CRPA) and Acinetobacter baumannii (CRAB) isolates obtained from clinical samples at Mulago hospital. Additionally, the mobility potential of carbapenem resistance genes via class 1 integrons in these isolates was also investigated. Methodology: Using 46 consecutive CRPA and CRAB isolates, antimicrobial susceptibility testing using the Kirby Bauer disk diffusion technique was performed. Furthermore, phenotypic assays (MHT, MBL, KPC) and genotypic assays for detection of carbapenemase production, carbapenemase encoding genes and class 1 integrons were also performed. Also, conjugation experiments to demonstrate the mobility potential of carbapenemase encoding genes in the isolates were also performed. Results: Of the Metallo β-lactamase encoding genes screened for, only the Verona Integron encoded Metallo-β-lactamase, blaVIM was present and was found in all the study isolates. Furthermore, Oxacillinase encoding genes, blaOXA-23, blaOXA-24 and blaOXA-51 were found present in 29%, 24% and 100% of the Acinetobacter isolates respectively, but absent in Pseudomonas isolates. Co-carriage of blaOXA-23 and blaOXA-24 was seen in 14% of the isolates. The carbapenemase producing isolates were all multi-drug resistant. However, were all susceptible to colistin. 63% of the isolates carried class 1 integrons. Of these, 31% successfully transferred class 1 integron containing blaVIM to azide resistant E.coli-J3 in the conjugation experiments. Conclusions: blaVIM and blaOXA-23 are the most prevalent carbapenemase encoding genes at Mulago Hospital, blaVIM and blaOXA-23, 24 and 51 are the genes mediating carbapenem resistance in our setting, the blaOXA-58 is possibly being replaced by blaOXA-23, carbapenemase producing isolates in this setting are multi-drug resistant and class 1 integrons are playing a role in dissemination of carbapenem resistance and other resistances seen in these isolates at Mulago Hospital.