NDM-1- and OXA-23-producing Acinetobacter baumannii isolated from intensive care unit patients in Tunisia

•High prevalence of imported/acquired carbapenem-resistant A. baumannii (CRAB) faecal carriage among ICU patients.•OXA-23 was the most frequent carbapenemase among identified CRAB, followed by NDM-1.•Co-occurrence of carbapenem and aminoglycoside resistance genes among multidrug-resistant A. baumannii.•Circulation of clonally related CRAB strains. Gastrointestinal colonisation by carbapenem-resistant Acinetobacter baumannii (CRAB) is a critical step before nosocomial infection. This study evaluated CRAB intestinal carriage in patients admitted to a Tunisian ICU and determined the antimicrobial resistance mechanisms involved. From December 2014 to February 2015, all 63 patients admitted to the ICU were screened for rectal CRAB colonisation upon admission and once weekly thereafter. ICU patients who acquired a CRAB nosocomial infection were also included. β-Lactamases and associated resistance genes were screened by PCR sequencing, and molecular typing was performed by PFGE and MLST. The CRAB faecal carriage rate at admission was 4.8% (3/63). The CRAB acquisition rate during ICU stay was analysed in 39 of the remaining 60 patients and the rate of acquired CRAB faecal carriage was 15.4% (6/39); 4 patients also showed an ICU-acquired CRAB infection (one patient was a faecal carrier and suffered infection). Overall, 13 CRAB isolates were collected from 12 patients, of which 11 isolates showed resistance to all antibiotics tested except colistin. blaOXA-23 and blaNDM-1 were detected in 11 and 2 isolates, respectively. All OXA-23-producing strains carried armA, tetB, sul1 and catB, and some of them carried aph(3′)-VIa, blaTEM-1, aph(3′)-Ia and ant(2′′)-Ia. The blaNDM-1-positive isolates harboured aph(3′)-VIa and catB. Three PFGE patterns and two STs were identified [ST195 (n = 11), ST1089 (n = 2, NDM-1-positive)]. Whether imported or acquired during ICU stay, CRAB colonisation is a major risk factor for the occurrence of serious nosocomial infection. Systematic screening of faecal carriage is mandatory to prevent their spread.