Comparison of 3 phenotypic-detection methods for identifying plasmid-mediated AmpC beta-lactamase-producing Escherichia coli, Klebsiella pneumoniae, and Proteus mirabilis strains.
BACKGROUND
Plasmid-mediated AmpC beta-lactamases (PABLs) have been detected in the strains of Escherichia coli, Klebsiella spp., Proteus mirabilis, and Salmonella spp. PABLs may be difficult to detect and might interfere in the therapeutic and infection-control processes. Although several PABL-detection methods based on phenotypes have been reported, the Clinical and Laboratory Standards Institute currently does not recommend a routine detection method for PABLs. The aim of this study is to compare the performances of 3 phenotypic PABL detection methods.


METHODS
Total 276 non-duplicated clinical isolates of E. coli (N=97), K. pneumoniae (N=136), and P. mirabilis (N=43) were collected from 14 hospitals in Korea between April and June 2007 in a non-consecutive and non-random manner. Multiplex PCR was performed to detect the PABL genes. Further, 3 phenotypic detection methods-cephamycin-Hodge test, Tris-EDTA (TE) disk test, and combination-disk test with 3-aminophenylboronic acid (BA)-were performed using cefoxitin and cefotetan disks.


RESULTS
PABL genes were detected by multiplex PCR in 122/276 isolates, including 14/97 E. coli, 105/136 K. pneumoniae, and 3/43 P. mirabilis isolates. The combination-disk test with BA showed higher sensitivity (98.4%), specificity (92.2%), and efficiency (96.3%) than the cephamycin-Hodge (76.2%, 96.1%, and 88.6%, respectively) and the TE-disk (80.3%, 91.6%, and 87.9%, respectively) tests.


CONCLUSIONS
The combination-disk test with BA is a simple, efficient, and interpretable test that can be applicable in clinical laboratories involved in the detection of PABLs in clinical isolates of E. coli, K. pneumoniae, and P. mirabilis.
Lee
Wookeun
W
Department of Laboratory Medicine, CHA University, Sungnam, Korea.
Jung
Bochan
B
Hong
Seong Geun
SG
Song
Wonkeun
W
Jeong
Seok Hoon
SH
Lee
Kyungwon
K
Kwak
Hyo Sun
HS
D000900:Anti-Bacterial Agents / Q000494:pharmacology; D001426:Bacterial Proteins / Q000032:analysis*; D015313:Cefotetan / Q000494:pharmacology; D002440:Cefoxitin / Q000494:pharmacology; D052978:Disk Diffusion Antimicrobial Tests / Q000379:methods*; D004926:Escherichia coli / Q000235:genetics / Q000302:isolation & purification*; D006801:Humans; D007711:Klebsiella pneumoniae / Q000235:genetics / Q000302:isolation & purification*; D010641:Phenotype; D010957:Plasmids; D011513:Proteus mirabilis / Q000235:genetics / Q000302:isolation & purification*; D012680:Sensitivity and Specificity; D001618:beta-Lactamases / Q000032:analysis*
D000900:Anti-Bacterial Agents; D001426:Bacterial Proteins; D015313:Cefotetan; D002440:Cefoxitin; C048795:AmpC beta-lactamases; D001618:beta-Lactamases