bla_VIM- and bla_OXA-mediated carbapenem resistance among Acinetobacter baumannii and Pseudomonas aeruginosa isolates from the Mulago hospital intensive care unit in Kampala, Uganda

Background: Between January 2015 and July 2017, we investigated the frequency of carbapenem resistant Acinetobacter baumannii (CRAB) and carbapenem resistant Pseudomonas aeruginosa (CRPA) at the Mulago Hospital intensive care unit (ICU) in Kampala, Uganda. Carbapenemase production and carbapenemase gene carriage among CRAB and CRPA were determined; mobility potential of carbapenemase genes via horizontal gene transfer processes was also studied.

Methods: Clinical specimens from 9269 patients were processed for isolation of CRAB and CRPA. Drug susceptibility testing was performed with the disk diffusion method. Carriage of carbapenemase genes and class 1 integrons was determined by PCR. Conjugation experiments that involved bla_VIM positive CRAB/CRPA (donors) and sodium azide resistant Escherichia coli J53 (recipient) were performed.

Results: The 9269 specimens processed yielded 1077 and 488 isolates of Acinetobacter baumannii and Pseudomonas aeruginosa, respectively. Of these, 2.7% (29/1077) and 7.4% (36/488) were confirmed to be CRAB and CRPA respectively, but 46 were available for analysis (21 CRAB and 25 CRPA). Majority of specimens yielding CRAB and CRPA were from the ICU (78%) while 20 and 2% were from the ENT (Ear Nose & Throat) Department and the Burns Unit, respectively. Carbapenemase assays performed with the MHT assay showed that 40 and 33% of CRPA and CRAB isolates respectively, were carbapenemase producers. Also, 72 and 48% of CRPA and CRAB isolates respectively, were metallo-beta-lactamase producers. All the carbapenemase producing isolates were multidrug resistant but susceptible to colistin. bla_VIM was the most prevalent carbapenemase gene, and it was detected in all CRAB and CRPA isolates while bla_OXA-23 and bla_OXA-24 were detected in 29 and 24% of CRAB isolates, respectively. Co-carriage of bla_OXA-23 and bla_OXA-24 occurred in 14% of CRAB isolates. Moreover, 63% of the study isolates carried class 1 integrons; of these 31% successfully transferred bla_VIM to E. coli J53.

Conclusions: CRAB and CRPA prevalence at the Mulago Hospital ICU is relatively low but carbapenemase genes especially bla_VIM and bla_OXA-23 are prevalent among them. This requires strengthening of infection control practices to curb selection and transmission of these strains in the hospital.