Background: Klebsiella pneumoniae is a common cause of nosocomial infection and is resistant to multiple antibiotics,
including β-lactams. It excretes extended spectrum β-lactamase (ESBL), an enzyme capable of hydrolyzing almost all β-lactams. Carbapenems including imipenem are drugs of choice for the treatment of infections caused by ESBL-producing
Enterobacteriaceae.
Objective: This study aimed to determine minimum inhibitory concentration (MIC) of imipenem in ESBL-producing K. pneumoniae isolates from patients admitted to Sappasitthiprasong Hospital.
Material and Method: A total of 250 non-repetitive K. pneumoniae isolates were collected from patients admitted to
Sappasitthiprasong Hospital between September 2014 and October 2015 and then screened for ESBL production by double
disk synergy test and determined for antimicrobial susceptibility by disk diffusion method. A total of 100 ESBL-producing
K. pneumoniae isolates were determined for the MICs of imipenem and ceftazidime. The resistant strain was further to
determined for MIC of meropenem.
Results: All ESBL-producing K. pneumoniae were resistant to ceftazidime in vitro with MICs of >64 μg/mL. Ninety-nine isolates expressing ESBL were susceptible to imipenem with MIC range of 0.25-2 μg/mL. One out of the 100 ESBL-positive K. pneumoniae strains was resistant to imipenem with MIC of >64 μg/mL. It was resistant to all antibiotics, including meropenem.
Conclusion: ESBL-producing K. pneumoniae can hydrolyze ceftazidime. However, imipenem was effective against ESBL-producing K. pneumoniae strains. Further characterization of ESBL types is required.

Keywords: Klebsiella pneumoniae, ESBL, Imipenem