Molecular characterization of carbapenemases of clinical Acinetobacter baumannii-calcoaceticus complex isolates from a University Hospital in Tunisia

The aim of this study was to identify the carbapenemases from clinical carbapenem-resistant Acinetobacter baumannii-calcoaceticus complex (CRABC) isolates and to assess their potential dissemination by conjugation and natural transformation. CRABC (n=101) were collected consecutively from inpatients of the University Hospital of Monastir, Tunisia, from 2013 to 2016. Antimicrobial susceptibility was determined by the disk diffusion method and E-test. Carbapenemase-encoding genes were screened by PCR. Genotyping was performed by Pasteur MLST scheme. Isolates were resistant to all beta-lactams, fluoroquinolones and aminoglycosides while 80 and 90% were susceptible to tigecycline and colistin, respectively. Resistance and intermediate resistance to imipenem were 87 and 13%, respectively. The genes bla(OXA-24)-like, bla(OXA-58)-like, blaca(OXA143)-like, bla(OXA-48)-like, bla(VIM), bla(IMP), and bla(KPC) were not found. The bla(OXA_51)-like and bla(OXA-23)-like genes were present in 100 and 82.17% isolates, respectively. One isolate (< 1%) carried bla(NDM_1) and bla(OXA-51)-like and belonged to Sequence Type 85 (ST85). Absence of transconjugants suggests a chromosomal location of NDM-1 determinant. The bla(NDM-1) gene was inserted in a truncated form of Tn125, which may explain the absence of bla(NDM_1) carrier-transformants. To our knowledge, this is the first report of the finding of NDM-positive A. baumannii in Tunisian territory. The study shows that despite the low prevalence and potential spread of NDM-1 enzyme among CRABC, continuous regional antimicrobial resistance surveillance and improved infection control measures are required in Tunisia to prevent further dissemination.