[Phenotypic detection of beta-lactamases production in Enterobacteriaceae]

Beta-lactam antibiotics are the most commonly used antibacterial drugs. However, many bacteria have developed resistance to these antibiotics, and the most common form of resistance is the production of beta-lactamase enzymes. Many members of the Enterobacteriaceae family produce different types of these enzymes.

The aim of this study was to perform phenotypic detection of production and identification of beta-lactamase type in Enterobacteriaceae isolated from different clinical specimens from patients hospitalized in the Clinical Center of Serbia.

The strains of Enterobacteriaceae were collected between November 2011 and January 2012 in the laboratory of the Clinical Center of Serbia.The isolates were identified according to the standard microbiology procedures and confirmed by the Vitek2 automated system. Antimicrobial susceptibility testing was performed by the disk diffusion method, and the phenotypic detection of production and identification of beta-lactamases was performed according to previously described methodologies.

In this study, a total of 172 Enterobacteriaceae strains were isolated. Further testing was performed on 54/145 (37.2%) strains showing decreased susceptibility to beta-lactam antibiotics: 13/85 (15.3%) Escherichia coli, 31/46 (67.4%) Klebsiella pneumoniae and 10/14 (71.4%) Proteus mirabilis. Among them, 40/145 (27.6%) strains produced extended spectrum beta-lactamases (ESBLs), 9/145 (6.2%)--AmpC, 1/145 (0.7%)--K1 beta-lactamase and 4/145 (2.8%)--carbapenemases. Carbapenemases were predominantly detected in K. pneumoniae (75%).

Enterobacteriaceae produce different types of beta-lactamases, and the most common type in our study was ESBLs. Production of carbapenemases detected in Enterobacteriaceae is also an associated problem.