[Investigation of plasmid mediated AmpC beta-lactamases among Escherichia coli and Klebsiella pneumoniae isolated from blood cultures].

The aim of this study was to investigate the prevalence and types of plasmid-mediated AmpC (pAmpC) beta-lactamase enzymes in Escherichia coli and Klebsiella pneumoniae strains isolated from blood cultures of hospitalized patients in Dokuz Eylul University Hospital between 2007 and 2012. A total of 261 isolates which consisted of 184 E.coli (70.5%) and 77 K.pneumoniae (29.5%) were included in the study. All isolates were resistant to cefotaxime and/or ceftazidime but susceptible to imipenem. Cefoxitin resistance was investigated as an indicator of AmpC type enzymes. A total of 57 (21.8%) isolates which were cefoxitin-resistant (32 E.coli, 25 K.pneumoniae), were screened for pampC genes by a multiplex polymerase chain reaction (PCR) assay. Additionally, 10 of each cefoxitin susceptible isolates per year were chosen randomly and screened by the same PCR assay to detect the presence of ACC enzymes, which can not hydrolyze cefoxitin. Positive PCR results were confirmed by sequence analysis. Plasmid analysis and macrorestriction analysis were performed for pampC-positive isolates. The presence of pAmpC enzymes has been shown in 9.4% (3/32) of cefoxitin-resistant E.coli, and 8% (2/25) of cefoxitin-resistant K.pneumoniae strains. It was noted that there were no strains producing this enzyme isolated in 2007 and 2008, however the prevalence of pAmpC was detected as 1.6% in 2009 (one ACT-1 producing K.pneumoniae), increasing to 4.8% in 2011 (one ACT-1 producing K.pneumoniae) and 6.4% in 2012 (three CMY-2 producing E.coli). These enzymes were found to be carried on 81 kb size plasmids in K.pneumoniae isolates and on a 9 kb size plasmid in E.coli isolates. Macrorestriction analysis indicated that two of the three CMY-2 producing E.coli had the same PFGE (Pulsed-field gel electrophoresis) pattern. If these two strains are considered as identical, it can be concluded that the prevalence of pAmpC was low in the strains isolated between 2007-2012 (4/261; 1.5%) in our institution. On the other hand, the increasing prevalence of pAmpC in 2011 and 2012 should be considered as a warning for the implementation of infection control measures and monitorization of the prevalence in order to prevent the dissemination of pAmpC. As far as the current literature is concerned, this is the first study that demonstrated the presence of the ACT-1 enzyme in K.pneumoniae isolates in Turkey.