title: Evaluation of the ability of four ESBL-screening media to detect ESBL-producing Salmonella and Shigella.
abstract: BACKGROUND
  The aim of this study was to compare the ability of four commercially available media for screening extended-spectrum beta-lactamase (ESBL) to detect and identify ESBL-producing Salmonella and Shigella in fecal samples. A total of 71 Salmonella- and 21 Shigella-isolates producing ESBL(A) and/or AmpC, were received at Norwegian Institute of Public Health between 2005 and 2012. The 92 isolates were mixed with fecal specimens and tested on four ESBL screening media; ChromID ESBL (BioMèrieux), Brilliance ESBL (Oxoid), BLSE agar (AES Chemunex) and CHROMagar ESBL (CHROMagar). The BLSE agar is a biplate consisting of two different agars. Brilliance and CHROMagar are supposed to suppress growth of AmpC-producing bacteria while ChromID and BLSE agar are intended to detect both ESBL(A) and AmpC.
  
  
  RESULTS
  The total sensitivity (ESBL(A)+AmpC) with 95% confidence intervals after 24 hours of incubation were as follows: ChromID: 95% (90.4-99.6), Brilliance: 93% (87.6-98.4), BLSE agar (Drigalski): 99% (96.9-100), BLSE agar (MacConkey): 99% (96.9-100) and CHROMagar: 85% (77.5-92.5). The BLSE agar identified Salmonella and Shigella isolates as lactose-negative. The other agars based on chromogenic technology displayed Salmonella and Shigella flexneri isolates with colorless colonies (as expected). Shigella sonnei produced pink colonies, similar to the morphology described for E. coli.
  
  
  CONCLUSIONS
  All four agar media were reliable in screening fecal samples for ESBL(A)-producing Salmonella and Shigella. However, only ChromID and BLSE agar gave reliable detection of AmpC-producing isolates. Identification of different bacterial species based on colony colour alone was not accurate for any of the four agars.
authors.forename: Kjersti
authors.initials: K
authors.lastname: Sturød
authors.forename: Ulf R
authors.initials: UR
authors.lastname: Dahle
authors.forename: Einar Sverre
authors.initials: ES
authors.lastname: Berg
authors.forename: Martin
authors.initials: M
authors.lastname: Steinbakk
authors.forename: Astrid L
authors.initials: AL
authors.lastname: Wester
mesh_terms: D001431:Bacteriological Techniques / Q000379:methods*; D003470:Culture Media / Q000737:chemistry*; D005243:Feces / Q000382:microbiology; D006801:Humans; D012475:Salmonella / Q000201:enzymology* / Q000254:growth & development / Q000302:isolation & purification; D012680:Sensitivity and Specificity; D012760:Shigella / Q000201:enzymology* / Q000254:growth & development / Q000302:isolation & purification; D001618:beta-Lactamases / Q000378:metabolism*
chemical_list: D003470:Culture Media; D001618:beta-Lactamases