Keywords b-Lactamase, Bulgaria, CTX-M-15, ESBL, Escherichia coli, Klebsiella pneumoniae

During a survey of extended-spectrum b-lactamase (ESBL)-producing Enterobacteriaceae in Bulgaria in 2001‐2002, three isolates from Sofia (two Escherichia coli ,o neKlebsiella pneumoniae) showed cefotaxime MICs that were decreased in the presence of clavulanate and were 2‐8-fold higher than those of ceftazidime. Resistance was transferred to a sensitive recipient strain of E. coli. Both wild-type and transconjugant strains produced a cefotaxime-hydrolysing b-lactamase of pI 8.8. Sequencing of the PCR product obtained with oligonucleotide primers binding outside the coding region identified this b-lactamase as CTX-M-15. To our knowledge, this is the first report of CTX-M-15 in Bulgaria.