RESUMEN
The susceptibility to cefoperazone/sulbactam of 197 strains of Gram-negative rods demonstrating an ESBL-positive phenotype was determined. The assortment of the investigated strains was as follows (numbers of strains are given in the brackets): E. cloacae (63), S. marcescens (46), K. pneumoniae (21), P. mirabilis (17), E. coli (9), P. vulgaris (8), P. aeruginosa (20) and A. baumanni (13). 83 strains from 197 were susceptible (42.1%). The MIC values were determined and the disc-diffusion method was performed. The susceptibilities among particular species were as follows (the order of data in the brackets is: % of the susceptible strains/MIC50/MIC90): E. cloacae (54.0/16/64), S. marcescens (23.9/64/> or = 128), K. pneumoniae (38.1/32/64), P. mirabilis (41.2/32/64), E. coli (44.4/32/32), P. vulgaris (75.0/8/32), P. aeruginosa (35.0/32/64), A. baumannii (46.2/32/64). Using disc-diffusion method, for 184 strains the difference between diameter of the inhibition zone around the disc with cefoperazone and the disc with cefoperazone/sulbactam was calculated. This difference amounted 5 mm or more in the case of 76.6% of the investigated strains. The results indicate that the comparison of the inhibition zones around cefoperazone and cefoperazone/sulbactam discs may be an additional method useful for phenotypic detection of ESBL producing organisms. These results highly correlated with results obtained by using analogous test with cefpirome and cefpirome/clavulanic acid (85.6% of concordance).