Testing of antibiotic combinations in NDM-1-producing nosocomial carbapenem resistant Acinetobacter baumannii

Carbapenem resistant Acinetobacter baumannii (CRAB) have become a serious problem in health care settings. Its high prevalence has been associated with nosocomial transmission, high mortality rates, drug resistance and massive economic loss. The most frequent mechanisms of resistance are carbapenem-hydrolyzing class D β-lactamases (CHDL), followed by class B metallo-β-lactamases (MBL). New Delhi metallo-β-lactamase-1(NDM-1) generated much global alarm and were labeled as superbugs which documented impossible to be treated. Preceding our study, eight different antibiotic combinations were evaluated using checkerboard method. This was based on the results obtained from antimicrobial susceptibility testing and phenotypic detection of metallo-β-lactamase production of 27 CRAB selected from our previous work. The existence of NDM-1 gene was tested using two different methods. All antibiotic combinations showed synergistic significant results and no antagonism activity was found. The percentage of NDM-1 gene in the first detection procedure was 12/27 (44.44%) were positive while the other negative 15 ones, 10/15 (66.67%) poses NDM-1were found when using the second method. PCR products were then verified by DNA sequencing. The final consensus sequences were analyzed and submitted to NCBI GenBank data base, representing accession numbers: (HQ6526091), (MK682763.1), (MK682764.1), (MK682767.1), (MN251665.1), (MN251666.1) and (MN251670.1). The alignments showed similarity ranged from 94%-100% nucleotides identity. We concluded that detection of CRAB using accurate, rapid methods and supplying hospital laboratories with molecular department for typing of pathogenic bacteria are essential. Each hospital should establish its own policies according to their antibiogram, national and international guidelines. Primary caretakers should comply with the implemented policies.