A CTX-M extended-spectrum β-lactamases-producing Klebsiella pneumonia isolated in Beijing

Objective To determine the ESBLs of Klebsiella pneumoniae and ESBL typing by molecular genetic procedures. Methods MIC test and ESBLs confirmation test were taken by agar dilution method in 80 strains of Klebsiella pneumoniae isolated in Beijing area from July 1999 to December 1999. To the 20 ESBLs positive conjugates isoelectric focusing was given. And nucleotide sequencing was analysed to conjugate strain CK23. Results 28 (35%) of the 80 strains of Klebsiella pneumoniae produced ESBLs. In the 28 strains, 20 were successfully done with conjugation of resistant plasmid. Isoelectric focusing results revealed that 13 (65%) of the 20 strains produced an ESBLs protein with a pI of 8.8 with or without additional pI 7.6 and pI 5.4. These β lactamases were all inhibited by clavulanite acid. The strains with pI=8.8 protein were highly resistant to cefotaxime and ceftriaxone but were susceptible or intermediate to ceftazidime. We picked CK23 strain out from 13 conjugates for gene cloning by the primers designed for bla CTX M and nucleotide sequencing. The results showed that the ESBLs gene in CK23 was CTX M, highly similar to CTX M 3 but had 3 amino acids, which were Glu39Gly, Leu122Pro, Asp278His. Conclusions 28 (35%) of the 80 strains of Klebsiella pneumoniae produced ESBLs. Resistant plasmid successfully conjugated in 20 of the 28 ESBLs producing strains. 13 of the 20 (65%) conjugates pruduced a pI =8.8 ESBLs,which was CTX M ESBLs,with only 3 amino acids different from CTX M 3. This paper indicated that a type of CTX M ESBLs existed in Klebsiella pneumoniae in Beijing, which specifically confers resistance to cefotaxime.