Microbiological and molecular detection of VIM-1 metallo beta lactamase-producing Acinetobacter baumannii.

Background: Acinetobacter resistant to carbapenems, is one of the most frequently isolated pathogens in the hospital settings and presents a challenge to the clinician.

Aim: to detect metallo-β-lactamase in A. baumannii by E-test and VIM-1 genes by PCR.

Materials And Methods: A four-month prospective study was done on Forty eight carbapenem resistant A. baumannii strains that isolated from patients with different types of infection either admitted or attending to the Outpatient Clinics at King Fahd Hospital in Al-Madinah Al-Monawarah. For all collected specimens, microbiological analysis, antimicrobial susceptibility testing using disk diffusion method, metallo Beta-lactamases (MBLs) detection by E-test (Epsilometer test) and VIM-1 metallo b-lactamase detection by PCR (polymerase chain reaction) were performed.

Results: Among the 48 carbapenem resistant A. baumannii isolates, 13 strains had MBL detected by E-test and among them VIM-1 gene was detected by PCR in 8 isolates but among the 35 A. baumannii isolates that did not produce MBL by E-test, VIM-1 gene was detected in 5 isolates.

Conclusions: The study revealed that specificity of the E-test is low, thus overestimating the number of MBL-positive isolates while, reduction of blaVIM-1 gene expression, revealing hidden MBL phenotypes. So, all carbapenem resistant isolates should be tested by PCR regardless of whether the conventional MBL testing is performed.