title: High frequency of co-resistance in CTX-M-producing Escherichia coli to non-beta-lactam antibiotics, with the exceptions of amikacin, nitrofurantoin, colistin, tigecycline, and fosfomycin, in a county of Sweden.
abstract: BACKGROUND
  The objective of this study was to investigate the in vitro activity of different antibiotics against CTX-M-producing Escherichia coli in a county of Sweden, and to determine the occurrence of multi-resistance and plasmid- mediated quinolone resistance among these isolates.
  
  
  METHODS
  A total of 198 isolates of E. coli with extended-spectrum beta-lactamase (ESBL) phenotype and mainly CTX-M genotype were studied. The minimum inhibitory concentrations (MICs) for amikacin, chloramphenicol, ciprofloxacin, colistin, fosfomycin, gentamicin, nalidixic acid, nitrofurantoin, tigecycline, tobramycin, trimethoprim, and trimethoprim-sulfamethoxazole were determined with the Etest. Susceptibility was defined according to the breakpoints of the European Committee on Antimicrobial Susceptibility Testing (EUCAST). MIC50 and MIC90 values were calculated.
  
  
  RESULTS
  Ninety-five percent or more of the isolates were susceptible to amikacin, nitrofurantoin, colistin, tigecycline, and fosfomycin. CTX-M group 9 was more susceptible than CTX-M group 1 to ciprofloxacin, gentamicin, and tobramycin. Sixty-eight percent of the isolates were multi-resistant, and the most common multi-resistance pattern was ESBL phenotype with decreased susceptibility to trimethoprim, trimethoprim-sulfamethoxazole, ciprofloxacin, gentamicin, and tobramycin. Only 1 isolate carried a qnrS1 gene, but 37% carried aac(6')-Ib-cr.
  
  
  CONCLUSIONS
  A high frequency of co-resistance between ESBL-producing E. coli and non-beta-lactam antibiotics was seen. On the other hand, very high susceptibility was seen for amikacin, nitrofurantoin, colistin, tigecycline, and fosfomycin. These data support the replacement of gentamicin and tobramycin, normally used in Sweden, with amikacin, for severe infections.
authors.affiliation: Clinical Microbiology, Department of Clinical and Experimental Medicine, Faculty of Health Sciences, Linköping University, Linköping, Sweden.
authors.forename: Åse
authors.initials: Å
authors.lastname: Östholm Balkhed
authors.forename: Maria
authors.initials: M
authors.lastname: Tärnberg
authors.forename: Hans-Jürg
authors.initials: HJ
authors.lastname: Monstein
authors.forename: Anita
authors.initials: A
authors.lastname: Hällgren
authors.forename: Håkan
authors.initials: H
authors.lastname: Hanberger
authors.forename: Lennart E
authors.initials: LE
authors.lastname: Nilsson
mesh_terms: D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D024881:Drug Resistance, Bacterial; D004926:Escherichia coli / Q000187:drug effects* / Q000201:enzymology / Q000302:isolation & purification; D004927:Escherichia coli Infections / Q000453:epidemiology / Q000382:microbiology*; D006801:Humans; D008826:Microbial Sensitivity Tests; D018709:Statistics, Nonparametric; D013548:Sweden / Q000453:epidemiology; D001618:beta-Lactamases / Q000096:biosynthesis*
chemical_list: D000900:Anti-Bacterial Agents; D001618:beta-Lactamases