Co-occurrence of aminoglycoside and β-lactam resistance mechanisms in aminoglycoside- non-susceptible Escherichia coli isolated in the Zurich area, Switzerland

The co-occurrence of aminoglycoside and beta-lactam resistance was assessed in 3358 consecutive Escherichia coli clinical isolates collected in 2014 in the greater Zurich area, Switzerland. Non-susceptibility to at least one of the tested aminoglycosides was observed in 470/3358 E. coli strains (14%). In strains categorized as broad-spectrum beta-lactamase (BSBL)-producers (1241/3358 isolates), extended-spectrum beta-lactamase (ESBL)-producers (262/3358) and AmpC-producers (66/3358), resistance to aminoglycoside was found in 23%, 52% and 20% of the isolates, respectively. In contrast, aminoglycoside-susceptible strains were rarely resistant to beta-lactams (33/1777, 1.9%). The genomes of 439 aminoglycoside-resistant E. coli were sequenced and aminoglycoside and beta-lactam genotypes were analysed. The most prevalent aminoglycoside resistance genes were aph(3')-Ia (133 strains, 30.3%), aac(3)-IId (100 strains, 22.8%), and aac(6')-Ib-cr (52 strains, 11.8%). The most frequent associations with beta-lactam resistance genes were aph(3')-Ia or aac(3)-IId with bla TEM-1 (94 and 72 strains, respectively), and aac(3)-IIa/aac(6')-Ib-cr with bla CTX-M-15 /bla OXA-1 (23 strains). These results indicate a frequent association of aac(3) and aph(3') genotypes with BSBL production, and a frequent co-occurrence of aac(6') genes with ESBL production. The high rate of co-occurrence of aminoglycoside resistance and beta-lactamase production must be considered in combination therapy. (c) 2020 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY license. (http://creativecommons.org/licenses/by/4.0/)