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, bla OXA-143 -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 Tn 125 , 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.