Background: The objective of this study was to investigate the in vitro activity of different antibiotics against CTX-M-producing Escherichia coli, to determine the occurrence of multiresistance and plasmid mediated quinolone resistance among these isolates.
Methods: A total of 198 isolates of E. coli with ESBL phenotype and mainly CTX-M genotype, were studied. The MICs for amikacin, chloramphenicol, ciprofloxacin, colistin, fosfomycin, gentamicin, nalidixic acid, nitrofurantoin, tigecycline, tobramycin, trimethoprim and trimethoprim-sulphamethoxazole were determined with the Etest. Susceptibility was defined according to the breakpoints of the European Committee on Antimicrobial Susceptibility Testing (EUCAST). MIC(50) and MIC(90) values were calculated.
Results: ≥95% of isolates were susceptible to amikacin, nitrofurantoin, colistin, tigecyclin, and fosfomycin. CTX-M group 9 was more susceptible than CTX-M group 1 to ciprofloxacin, gentamicin, and tobramycin. 68% of the isolates were multiresistant, and the most common multi-resistance pattern was ESBL-phenotype with decreased susceptibility to trimethoprim, trimethoprim-sulphamethoxazol, ciprofloxacin, gentamicin and tobramycin. Only one isolate carried a qnrS1-gene, nine isolates carried aac(6’)-Ib-cr.
Conclusions: The high frequency of multi-resistance found in this study is alarming and it is urgent to find strategies to limit the emergence and spread of these multi-resistant strains.