[Application of four variants of the diagnostic disc test (CD01, CD02, CD03, CD04) for detection of ESBL-positive strains of gram-negative rods].

The aim of this study was to evaluate the usefulness of four variants of the diagnostic disc test (DD) to detect extended-spectrum beta-lactamases (ESBLs) in nosocomial strains of gram-negative rods. Also, the diagnostic disc test (DD) was compared with the double-disc synergy test (DDST) for the effectivity of ESBLs identification. A total number of 111 ESBL-positive (DDST-positive) strains of gram-negative rods isolated from hospitalized patients in 2004 was examined. Ninety nine strains belonged to enteric rods (89.2%) and twelve strains--to nonfermentative rods (10.8%). Two reference strains: E. coli ATCC 25922 (ESBL-negative one) and K. pneumoniae ATCC 700603 (ESBL-positive one) were included in the study. Four variants of the diagnostic disc test (DD, Oxoid Ltd, UK) were applied for ESBLs detection: CPD/CD01, CAZ/CD02, CTX/CD03 and CPO/CD04. All examined strains (111) were DDST-positive. Positive results in the DD test (Oxoid Ltd) were as follows: CPD/CD01--59 strains (53.2%), CAZ/CD02--80 strains (72.1%), CTX/CD03--92 strains (82.9%) and CPO/CD04--110 strains (99.1%). Discs containing cefpirome (CPO) and cefpirome with clavulanic acid (CD04) were the best set for detection of ESBLs in our collection of clinical gram-negative rods. Results of this variant of the DD test were the most consistent with the results of the DDST. Application of several disc diffusion methods to detect ESBL producers increases the probability of proper identification of these strains.