In Vitro Activity of Sulbactam–Durlobactam against Carbapenem-Resistant Acinetobacter baumannii Clinical Isolates: A Multicentre Report from Italy

Abstract

In the present study, the in vitro activity of the sulbactam-durlobactam (SUL-DUR) combination was evaluated against 141 carbapenem-resistant <i>A. baumannii</i> (CR<i>Ab</i>) clinical strains collected from six Italian laboratories. Over half (54.6%) of these isolates were resistant to colistin. The SUL-DUR combination was active against these CR<i>Ab</i> isolates with MIC₅₀ and MIC₉₀ values of 0.5 mg/L and 4 mg/L, respectively. Only eleven isolates were resistant to SUL-DUR with MIC values ranging from 8 to 128 mg/L. The SUL-DUR resistant <i>A. baumannii</i> exhibited several antimicrobial resistance genes (ARGs) such as <i>bla</i>_OXA-20, <i>bla</i>_OXA-58, <i>bla</i>_OXA-66, <i>bla</i>_ADC-25, <i>aac(6')-Ib3</i> and <i>aac(6')-Ib-cr</i> and mutations in <i>gyr</i>A (S81L) and <i>par</i>C (V104I, D105E). However, in these isolates, mutations Q488K and Y528H were found in PBP3. Different determinants were also identified in these CR<i>Ab</i> isolates, including <i>adeABC</i>, <i>adeFGH</i>, <i>adeIJK</i>, <i>abeS</i>, <i>abaQ</i> and <i>abaR</i>, which encode multidrug efflux pumps associated with resistance to multiple antibacterial agents. This is the first report on the antimicrobial activity of SUL-DUR against carbapenem-resistant <i>A. baumannii</i> isolates selected from multiple regions in Italy.