title: Comparison of detection methods for extended-spectrum beta-lactamases in Escherichia coli strains.
abstract: BACKGROUND
  Detection of extended-spectrum beta-lactamases (ESBLs) could be a major challenge for microbiologists--the difficulties arise mainly from the phenotypic differences among strains.
  
  
  METHODS
  Evaluation of ESBLs was performed on 42 strains of E. coli by: 1) DDST on MHA, 2) DDST on MHA with cloxacillin, 3) CT on MHA, according to CLSI, 4) CT on MHA with cloxacillin, 5) Etest ESBL (AB Biodisk), 6) CHROMagarTM ESBL (GRASO), 7) ChromID® ESBL (bioMérieux), and 8) automatic system VITEK2 ESBL test (bioMérieux).
  
  
  RESULTS
  Positive results were obtained for 20 strains using method 1, for 18 strains using method 2, 17 by method 3, 14 by method 4, 11 by method 5, 39 by method 6, 40 by method 7, and 15 by method 8. Using Etest ESBL 6.0 non-determinable results were obtained. The most consistent results were obtained when comparing the results of method 3 with results of method 2 (97.6%), and comparing the results obtained using methods 3 and 8 (95.2%).
  
  
  CONCLUSIONS
  Based on our study we conclude that the chromogenic media can only be used as a screening method for the detection of ESBLs in E. coli rods. Etest is less useful compared to other phenotype methods, due to the impossibility of obtaining results for all the tested strains. Adding cloxacillin to MHA does not increase the frequency of detection of ESBLs in E. coli strains. DDST seems to be the most reliable among phenotypic methods for the detection of ESBLs in E. coli rods.
authors.affiliation: Instytut Genetyki Człowieka Polskiej Akademii Nauk w Poznaniu.
authors.forename: Ewelina
authors.initials: E
authors.lastname: Kałużna
authors.affiliation: Katedra i Zakład Mikrobiologii, Collegium Medicum im. Ludwika Rydygiera w Bydgoszczy Uniwersytetu Mikołaja Kopernika w Toruniu.
authors.forename: Patrycja
authors.initials: P
authors.lastname: Zalas-Więcek
authors.affiliation: Katedra i Zakład Mikrobiologii, Collegium Medicum im. Ludwika Rydygiera w Bydgoszczy Uniwersytetu Mikołaja Kopernika w Toruniu.
authors.forename: Eugenia
authors.initials: E
authors.lastname: Gospodarek
mesh_terms: D000362:Agar; D003470:Culture Media; D004926:Escherichia coli / Q000145:classification* / Q000201:enzymology*; D008826:Microbial Sensitivity Tests / Q000379:methods*; D010641:Phenotype; D013045:Species Specificity; D001618:beta-Lactamases / Q000032:analysis* / Q000378:metabolism*
chemical_list: D003470:Culture Media; D000362:Agar; D001618:beta-Lactamases