Evaluation of the β-Lactamase Disk Test Method in the Detection of Extended-Spectrum-β-Lactamases in Clinical Isolates of Multidrug-Resistant Pseudomonas Aeruginosa

The production of extended-spectrum-?-lactamases (ESBLs) is the main mechanism of resistance to β-lactam antibiotics. The outbreak of isolates simultaneously possessing several resistance mechanisms to β-lactam antibiotics caused a decrease in sensitivity of the confirmatory tests for ESBL. The aim of this study was the evaluation of the β-lactamase disk test method in the detection of ESBLs in clinical isolates of multidrug-resistant Pseudomonas aeruginosa.
A total of 100 multidrug-resistant P. aeruginosa isolates were recovered from burn patients. The sensitivity of the isolates to different antibiotics was determined using the standard disk diffusion method. ESBL-producing isolates were detected through the combination disk test with clavulanic acid, double disk synergy test, and β-lactamase disk test. Carbapenemase-producing isolates were detected using the Modified Hodge Test (MHT). The ESBLs genes (blaTEM, blaOXA, blaPER, blaSHV, blaCTX-M and blaPSE) were determined through polymerase chain reaction (PCR).
All isolates were multidrug resistant. Only 3 isolates were detected as ESBL-producing isolates through combination disk test. No ESBL-producing isolates were detected through double disk synergy test. Among the 100 studied isolates, 87% were detected as ESBL-producing isolates and 68% as carbpenemase-producing isolates through β-lactamase disk test. The prevalence of blaTEM, blaOXA, and blaPER among isolates were 97%, 61%, and 13%, respectively. All isolates were negative for blaSHV, blaPSE, and blaCTX-M.
According to the results obtained in this study, the β-lactamase disk test is suitable for the detection of ESBLs in multidrug resistant isolates. However, further investigation is required.