Evaluation of Drigalski agar supplemented with ceftazidime (2 mg/L) for selective isolation of extended-spectrum beta-lactamase (ESBL) producing Enterobacteria

Abstract

The purpose of this study was to evaluate the performance of the Drigalski agar supplemented with 2 mg/L of ceftazidime (DC) for selective isolation of expanded-spectrum beta-lactamase (ESBL) producing Enterobacteria in clinical samples. The Drigalski agar supplemented with 2 mg/L of ceftazidime was compared with the chromID TM ESBL medium (bioMerieux, Marcy l'Etoile, France). Six strains from the collection of reference center for antibiotics of the Pasteur Institute of Paris and 247 clinical samples were used to calculate the performance and the intrinsic characteristics of DC medium, respectively. The main ESBL producing Enterobacteria consist of Escherichia coli (n=31; 44.3%), Klebsiella pneumoniae (n=19; 27.1%) and Enterobacter cloacae (n=12; 17.1%). ESBL producers were confirmed by synergy testing. The sensitivity (Se), specificity (Sp), positive predictive value (PPV) and negative predictive value (PPN) after 24 h of incubation at 37 degrees C were respectively 98.6, 98.7, 98.6 and 98.7%. The study shows that DC agar is a sensitive and specific medium for selective isolation of ESBL producing Enterobacteria, but the character chromogenic agar chromID TM ESBL remains an additional advantage in the identification of strains.