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Volume 45, Number 3, June 2012

Phenotypic detection and polymerase chain reaction screening of extended-spectrum b-lactamases produced by Pseudomonas aeruginosa isolates


Shih-Ping Lin, Meei-Fang Liu, Chin-Fu Lin, Zhi-Yuan Shi *


Received: April 30, 2011    Revised: July 14, 2011    Accepted: August 9, 2011   

 

Corresponding author:

Section of Infectious Diseases, Department of Internal Medicine, Taichung Veterans General Hospital, No. 160, Sec. 3, Chung-Kang Road, Taichung, 40705 Taiwan, ROC. E-mail address: poempin@vghtc.gov.tw (Z.-Y. Shi).



 

Background and purpose: 

 A growing number of b-lactamases have been reported in isolates. The aims of this study were to survey the types of extended-spectrum b-lactamases (ESBLs) by polymerase chain reaction (PCR), to evaluate the reliability of phenotypic tests for ESBLs, and to identify the clonal distribution by pulsed-field gel electrophoresis (PFGE) among P. aeruginosa isolates resistant to expanded-spectrum cephalosporins (ceftazidime, aztreonam, or cefepime).



 

Methods:

The antimicrobial susceptibility of 57 P. aeruginosa isolates from blood specimens were examined according to the recommendations of the Clinical Laboratory Standards Institute. ESBL phenotypes were determined by using cloxacillin-containing double disc synergy test (DDST). The existence of 11 b-lactamase genes was detected by PCR.



 

Results:

Of the 57 P. aeruginosa isolates, 35 (61.4%) isolates were PCR-positive for b-lactamase genes. Twelve of 35 isolates were PCR-positive for combination of ampC and ESBL genes, including TEM, GES, SHV, VEB and OXA-I genes. The sensitivity and specificity of cloxacillincontaining DDST (using the criteria of ceftazidime zone diameter increased S5 mm) were 84.1% and 54.5%, respectively. Nine clusters were classified among 35 PCR-positive isolates by PFGE. Isolates of clusters B and C were distributed in different wards of this hospital during a period of 3e4 years.



 

Conclusion:

ESBL genes are not uncommon in P. aeruginosa isolates. Cloxacillin-containing DDST can enhance the sensitivity and has a potential role for phenotypic detection of ESBL-producing P. aeruginosa, and PCR is also helpful for the identification of specific b-lactamase genes. These P. aeruginosa isolates were classified into several diverse clones

which could continue to spread in the hospital over a long period of time.


 

Key words:

Cloxacillin-containing double disc synergy test; Extended-spectrum b-lactamase; Polymerase chain reaction; Pseudomonas aeruginosa