Korean J Clin Pathol.  1997 Dec;17(6):1076-1088.

Detection of Extended-spectrum beta-lactamase in Klebsiella pneumoniae

• Lee SY
• Lee SH
• Pai CH

Abstract

BACKGROUNDS : Extended spectrum beta-lactamases (ESBL) are plasmid-mediated enzymes that confer broad-spectrum resistance to aztreonam, most penicillins, and cephalosporins including ceftazidime, cefotaxime and ceftriaxone. But with most routine susceptibility tests, ESBL-producing strains may not appear to be resistant, which makes it difficult to predict the effectiveness of the beta-lactam agents. In this study, we performed several test procedures to detect ESBL in blood isolates of Klebsiella pneumoniae and examined the risk factors for bacteremia due to ESBL-producing K. pneumoniae.
MATERIALS AND METHODS
Of 87 blood culture Isolates of K. pneumoniae during the first 7 month of 1996, 39 showed reduced susceptibilities to at least one of the 4 antibiotics, aztreonam, cefotaxime, ceftazidime and ceftriaxone. Twenty-three of the 39 isolates were assailable for screening for ESBL. Antibiotic resistance was tested by the agar dilution method and beta-lactamase assay using nitrocefin disks. Effect of beta-lactamase inhibition was examined by the doubledisk synergy test using aztreonam, cefotakime, ceftazldime, and ticarc illin/clavulanate disks and by ESBL Etest involving ceftazidime and cert tazidime/clavulanate. Ability to transfer the beta-lactam resistance was tested by conjugation. We also reviewed the medical records of the patients with K. pneumoniae. (21 with and 41 without ESBL) bacteremia to ananlyze their clinical characteristics.
RESULTS
Of 23 strains tested, reduced susceptibilities to cefotaxime, aztreon am and ceftazidime were shown in 23, 18, and 18 strains, respectively. All strains were positive for beta-lactamase and its activity was trasfered to E. coli in all strains. Activities of beta-lactamases were shown to be inhibited by clavulanate in 21 strains by the double-disk method, but in only 15 strains by the ESBL Etest. Nineteen of 21 bacteremia were nosocomially acquired. ESBL-producing strains were associated with length of hospitalization, stay in intensive care unit, use of invasive procedures and administration of antibiotics Including penicillins and third-generation cephalosporins.
CONCLUSIONS
Although an increasing incidence of and outbreaks by ESBL-producing strains are reported, detection of ESBLs has proved to be difficult. Using several testing methods such as double-disk synergy test, ESBL Etest and conjugation, we estimated that 40.9% of blood isolates of K. pneumoniae produce ESBL. We should pursue for more sensitive and reliable screening methods for the detection of ESBL.

MeSH Terms

Agar
Anti-Bacterial Agents
Aztreonam
Bacteremia
beta-Lactam Resistance
beta-Lactamases*
Cefotaxime
Ceftazidime
Ceftriaxone
Cephalosporins
Clavulanic Acid
Disease Outbreaks
Drug Resistance, Microbial
Hospitalization
Humans
Incidence
Intensive Care Units
Klebsiella pneumoniae*
Klebsiella*
Mass Screening
Medical Records
Penicillins
Pneumonia
Risk Factors
Agar
Anti-Bacterial Agents
Aztreonam
Cefotaxime
Ceftazidime
Ceftriaxone
Cephalosporins
Clavulanic Acid
Penicillins
beta-Lactamases