Phylogenetic analysis of carbapenem-resistant Acinetobacter baumannii isolated from different sources using Multilocus Sequence Typing Scheme
Anane Yaw Adjei, Sandeep Vasaikar, Teke Apalata, Emily Grace Okuthe, Sandile P. Songca
Abstract
The emergence and worldwide distribution of carbapenem-resistant Acinetobacter baumannii strains has become a major public health threat. The objective of this study was to investigate the clonal relatedness of A. baumannii isolates collected from clinical and extra-hospital environments in Mthatha, South Africa. Forty carbapenem-resistant isolates comprising of clinical (20) and extra-hospital (20) were identified and tested for antimicrobial susceptibility. Detection of carbapenemase encoding genes was performed by Real-time PCR. The clonal relationship of clinical isolates relative to extra-hospital isolates was determined via multilocus sequence typing (MLST). All isolates (clinical and extra-hospital) were resistant to most common antibiotics including carbapenems (imipenem; MIC ≥32 μg/mL and meropenem; MIC ≥32 μg/mL) with the only exception being amikacin (with 3 isolates susceptible), tigecycline (14 isolates susceptible) and colistin (all isolates susceptible). The bla OXA-23-like and the intrinsic bla OXA-51 -like genes were detected in all the isolates tested. The bla OXA-58-like and bla IMP-type genes were detected in 2 clinical isolates whilst the bla OXA-24-like, bla VIM-type, bla NDM-1, bla SIM, and bla AmpC were not detected. The bla OXA-24-like, bla OXA-58-like, bla IMP-type, bla VIM-type, bla NDM-1, bla SIM, and bla AmpC were negative in the extra-hospital isolates. Co-occurrence of bla OXA-23 -like, bla OXA-58-like and bla IMP-type was observed in 2 clinical isolates. The MLST performed on 33 isolates identified 5 existing sequence types (ST) (ST1, ST2, ST25, ST85 and ST215) in clinical isolates and 2 existing STs (ST1 and ST2) in extra-hospital isolates. The most dominant ST was ST2 accounting for 68.8% of the clinical isolates and 82.4% of the extra-hospital isolates. The study demonstrated high prevalence and potential clonal spread of globally-disseminated clonal complex 2 carrying bla OXA-23-like within our local settings. However, ST25 might be an emerging lineage carrying the bla OXA-23-like . Continuous monitoring is important in limiting the spread of these strains in other healthcare settings and the community.