Antibiotic resistance profiles of gram-negative bacteria in southern Tunisia: Focus on ESBL, carbapenem and colistin resistance

The main objective of this cross-sectional study was to investigate the prevalence of beta-lactam (cephalosporins or carbapenems) or colistin resistant bacteria. Those were isolated from urine samples in two private polyclinics located in the Sfax region, in southern Tunisia. From September 2021 to August 2022, 116 strains resistant to β-lactams or colistin were isolated, identified by MALDI-TOF, and their antibiotic susceptibility was assessed by disk diffusion method. Resistance genes were detected by real-time PCR, standard PCR, and sequencing. The results revealed that the 116 strains consisted predominantly of Enterobacteriaceae (92.2 %) and non-fermenting bacteria (7.8 %). Among these strains, 21 (18.1 %) were resistant to carbapenems, three (2.7 %) to colistin, including two strains of Klebsiella pneumoniae (1.7 %) exhibiting resistance to both carbapenems and colistin. In Enterobacteriaceae, bla_CTX-A, bla_SHV, and bla_TEM were found in 79.5 %, 46.7 %, and 40.2 % of strains, respectively. For these strains, the minimum inhibitory concentrations (MICs) of imipenem and ertapenem ranged from >32 to 6 μg/mL and > 32 to 2 μg/mL, respectively, with bla_OXA-48 and bla_NDM detected in 21.7 % and 19.6 % of isolates, respectively. Seven A. baumannii isolates resistant to imipenem and meropenem (MICs >32 μg/mL and 8 μg/mL, respectively) carried bla_OXA-23 (n = 5) and bla_OXA-24 (n = 2). In addition, mutations in the mgrB gene conferring colistin resistance were identified in two isolates. Two K. pneumoniae were colistin-resistant and carried the bla_OXA-48 gene. These results highlight the urgency of developing new strategies for the identification and surveillance of pathogenic strains in humans to effectively combat this growing public health threat in Tunisia.