In Vitro Activity of Ceftazidime-Avibactam against 3rd Generation Cephalosporin and Carbapenem Resistant Gram-Negative Bacteria Obtained from Blood and Fecal Samples of Hematopoietic Stem Cell Transplanted Patients

The recipients of hematopoietic stem cell transplantation (HSCT) tend to develop invasive infections because of the immunosuppression caused by the underlying disease or the transplantation itself. The gastro¬intestinal tract is the major source of causative agents, often demonstrating multidrug resistance. The aim of this study is to investigate the in vitro activity of ceftazidime-avibactam (CZA) against 3rd generation ceph¬alosporin and/or carbapenem resistant (CPR) Gram-negative bacteria obtained from blood and fecal sam¬ples of patients following HSCT. Thirty-five clinical isolates were studied (Enterobacterales, n=25, Pseu-domanas spp., n=8, A. baumannii, n=2). MALDI Biotyper (Bruker) and Phoenix system (BD) were used for identification and susceptibility testing. Multiplex PCR was performed to detect genes associated with beta-lactam resistance. In the studied group 96% of the enteric bacteria were Extended Spectrum Beta Lacta¬mase producers (ESBL) and all were susceptible to CZA. CZA demonstrated an excellent activity against piperacillin-tazobactam resistant isolates. Among the CPR isolates, 91% were CZA resistant and blaVIM, blaOXA-23 and blaOXA-24/40, blaOXA-48 genes were detected. In conclusion, an excellent activity of CZA against ESBL producing and piperacillin-tazobactam resistant Gram - negative isolates was found. Despite its potent activity against class A enzymes, avibactam failed to inactivate class B and class D carbapenemases.