Dio-Sensimedia: a novel culture medium for rapid detection of extended spectrum beta-lactamases

Abstract

Background: Resistance to contemporary broad-spectrum beta-lactams, mediated by extended-spectrum beta-lactamases (ESBL), is an increasing problem worldwide. Many of the emerging antimicrobial resistance problems of this decade have been characterized by difficulty in the recognition of resistance in the laboratory, particularly by rapid susceptibility test methods. The plasmid-encoded ESBL represent such a resistance phenomenon that is difficult to recognize. We compared Dio-Sensimedia-ES (DSM-ES; Diomed, Istanbul, Turkey) and Mueller-Hinton (MH) agar in the double-disk synergy test (DDST) as a novel rapid system for detecting ESBL directly from bacterial culture.

Methods: Sixty ESBL-producing Klebsiella pneumoniae isolates cultured from blood (30), endotracheal aspirates (20), urine (5) and pus (5), as well as 40 Escherichia coli isolates cultured from endotracheal aspirates (15), urine (10), blood (8) and pus (7) were studied. Isolates positive for ESBL by the combined disk tests were tested with the DDST using MH and DSM-ES agar to detect ESBL-mediated resistance in K. pneumoniae and E. coli. DSM-ES agar was also used to determine the susceptibility of Enterobacteriaceae and staphylococci.

Results: Among 60 ESBL-producing K. pneumoniae isolates, 59 (98.3%) were identified as ESBL-positive by the DDST using MH, and 58 (96.6%), using DSM-ES agar. Of 40 ESBL-producing E. coli isolates, 38 (95%) were ESBL-positive by the DDST on MH agar, and 37 (92.5%), on DSM-ES agar. The average incubation period required for ESBL detection by the DDST on DSM-ES agar was 4 hours.

Conclusions: Since the DDST results were available within 4 hours when DSM-ES agar was used, the use of this media may significantly lower the length of hospital stay, the total cost for patient care and even the mortality rate by facilitating early treatment against ESBL-producing organisms.

Figure 1

Red circle inhibition zone around the disk on the left, and at the top. Disks: centre, amoxycillin+clavulanate 20 + 10 μg; right, cefepime 30 μg; left, aztreonam 30 μg; top, ceftazidime 30 μg; bottom, ceftriaxone 30 μg.

Figure 2

Detection of ESBL production by the double disk test on DSM-ES agar. Disks: centre, amoxycillin+clavulanate 20 + 10 μg; right, cefepime 30 μg; left, ceftriaxone 30 μg; top, ceftazidime 30 μg; bottom, aztreonam 30 μg.