Paper Title
First Report of Detection of The Plasmid-Mediated MCR-1 Gene in Human Isolates of Acinetobacter Baumannii in Turkey

Abstract
Since the worldwide spread of extended-spectrum beta-lactamases (ESBL), especially carbapenemases, the antibiotics used to treat infections with Gram-negative bacteria have been limited. This challenge is partially overcome by combining beta-lactam antibiotics with aminoglycosides. Lately, however, the global increase in prevalence of the Gram-negative bacteria which resistant to both of the antibiotic groups have led to increased use of colistin. Unfortunately, resistance has also emerged to colistin, the major drug of last-resort that has extended-spectrum activity against Gram-negative bacteria. Recent studies have shown that colistin resistance can also be developed by acquisition of plasmid-mediated mcr-1 gene. Plasmids can harbour a lot of resistance genes together and these genes can be transferred horizontally both within and between species. We aimed to investigate the presence of plasmid-mediated mcr-1 gene which is responsible for colistin resistance and the possible correlations with beta-lactamase genes and plasmid-mediated aminoglycoside resistance genes in carbapenem- and aminoglycoside-resistant Acinetobacter baumannii isolated as the causative agents of healthcare-associated infections in a major regional hospital in Turkey. A total of 61 carbapenem- and aminoglycoside-resistant A. baumannii isolates were enrolled in the study. All isolates except one were colistin susceptible. Presence of the targeted resistance genes were investigated by using polymerase chain reaction (PCR) method. The mcr-1 gene was detected in four of 61 (%6.6) A. baumannii isolates. All of four mcr-1-positive isolates carried blaOXA-23-like gene. Additionally, the three of them were also blaTEM-positive and the other was blaTEM- and blaGES-positive. However, the single A. baumannii isolate which was clinically resistant to colistin carried only blaOXA-23-like gene. Our study is representing the first report of detection of the plasmid-mediated mcr-1 gene in human isolates of Acinetobacter baumannii in Turkey, even though they were clinically susceptible to colistin. These results may indicate a strong sign for emerging of clinically resistant isolates as upcoming threat. We can conclude that the rigorous screening of these resistance genes during the healthcare-associated infection outbreaks, is extremely critical for surveillance of healthcare-associated infections, rational antibiotic use and hereby decreasing mortality. Our study is ongoing. This research was supported by Scientific Research Projects Coordination Unit of Cukurova University. Key Words - Acinetobacter baumannii, colistin resistance, mcr-1, PCR.