Gram negative organisms take an important role in hospital infections and the -lactam antibiotic resistance due to ESBL is of İncreasing importance and this resistance is different among hospitals.

In this study our goal was to defermine the ESBL activity of 117 gram negative bacteria from Enterobacteria family caused hospital infections at Şişli Etfal Hospital during June 1998 – September 1999 and to define the antibiotic suscetibility using double disc synergy test ESBL was found out in 38 (32.5 %) of the isolates. ESBL was found out in 24 (47 %) of the 51 K.pneumoniae, in 6 (15.8 %) of the 38 E.coli, in 4 of the 9 E.aerogenes , in 1 of the 7 E.cloacea, in 1 of the 4 K.oxytoca, in one C.freundii and in one E.sakazakii.

According to our results the most effective antibiotics to the resistant isolates were carbapenems followed by quinolones and aminoglycosides