title: Evaluation of a new selective chromogenic agar medium for detection of extended-spectrum beta-lactamase-producing Enterobacteriaceae.
abstract: A novel chromogenic agar medium (ESBL-Bx; bioMérieux, Marcy l'Etoile, France) was compared to MacConkey agar supplemented with 2 mg ceftazidime/liter (MCKC) for the selective isolation and presumptive identification of extended-spectrum beta-lactamase (ESBL)-producing Enterobacteriaceae directly from clinical samples. Of a total of 644 clinical specimens (including 551 fecal samples), 496 yielded no growth and 148 yielded growth on one or both media. Overall, 44 ESBL-producing Enterobacteriaceae strains (Escherichia coli [n=17], Enterobacter aerogenes [n=17], Klebsiella spp. [n=5], and Citrobacter freundii [n=5]) were isolated from 37 specimens by a combination of both methods after 18 to 24 h of incubation. The sensitivities were 97.7 and 84.1% for ESBL-Bx and MCKC, respectively, with 43 ESBL-positive strains isolated as colored colonies from 36 specimens on ESBL-Bx versus 37 ESBL-positive organisms isolated from 32 specimens on MCKC. The specificities by specimens were 89 and 91% for ESBL-Bx and MCKC, respectively. On either one of the two media, natural AmpC-hyperproducing Enterobacter spp. (n=25) and Citrobacter spp. (n=14) were the most common false positives as well as non-ESBL-producing Klebsiella oxytoca (n=18) on ESBL-Bx and Morganella morganii (n=10) on MCKC. We conclude that ESBL-Bx is a sensitive and specific medium for the isolation of ESBL-producing Enterobacteriaceae from clinical samples. The main advantages of ESBL-Bx over MCKC reside in its chromogenic character and its sensitivity and selectivity, which enabled the recovery and presumptive identification of most ESBL-producing Enterobacteriaceae within 24 h and reduced by 27% the need for unnecessary identification and confirmation of ESBL testing when disregarding all colorless colonies growing on this medium.
authors.affiliation: Laboratoire de Bactériologie, Cliniques Universitaires UCL de Mont-Godinne, 1, Av. Dr Gaston Thérasse, B-5530 Yvoir, Belgium. youri.glupczynski@skynet.be
authors.forename: Youri
authors.initials: Y
authors.lastname: Glupczynski
authors.forename: Catherine
authors.initials: C
authors.lastname: Berhin
authors.forename: Caroline
authors.initials: C
authors.lastname: Bauraing
authors.forename: Pierre
authors.initials: P
authors.lastname: Bogaerts
mesh_terms: D000362:Agar; D000900:Anti-Bacterial Agents / Q000494:pharmacology; D002442:Ceftazidime / Q000494:pharmacology*; D002863:Chromogenic Compounds; D003470:Culture Media; D004755:Enterobacteriaceae / Q000145:classification* / Q000201:enzymology / Q000254:growth & development / Q000302:isolation & purification*; D005243:Feces / Q000382:microbiology; D006801:Humans; D012137:Respiratory System / Q000382:microbiology; D012680:Sensitivity and Specificity; D001618:beta-Lactamases / Q000096:biosynthesis*
chemical_list: D000900:Anti-Bacterial Agents; D002863:Chromogenic Compounds; D003470:Culture Media; D000362:Agar; D002442:Ceftazidime; D001618:beta-Lactamases