The investigation of plasmid profiles of Enterococcus faecalis strains isolated from mastitic cow milks

Plasmids are extrachromosomal elements have capable of transmitting antimicrobial resistance and virulence factor genes from bacteria to bacteria. An increase in the number of plasmids in strains shows patogenity of the strain is getting increased. Plasmid profile analysis is a one of the most practical molecular typing methods used for determining the clonal expansion in the flock. The purpose of this study was to investigate the plasmid profiles of Enterococcus faecalis isolated from cow milk samples with mastitis. As a material, 56 Enterococcus faecalis isolates isolated from 600 milk samples with mastitis were used. After the isolation of the enterococci in selective mediums, identifications on species basis were performed by polymerase chain reaction (PCR). Modified alkaline lysis method was used for plasmid isolation. Results revealed that 19 of 56 isolates have plasmids varying one to seven and lengths of those were ranged approximately between 1.7 kb and 41 kb. It was determined that five isolates have only one plasmid while the other 14 have more plasmids. Six clusters that containing two or more strains with similar plasmid profile were formed. Following the plasmid isolation, cluster analysis was performed between the same and similar plasmids after their profile contends checked. Some clues related to clonal expansion has been detected. This study is the first in Turkey that plasmid profiles of E. faecalis strains isolated from cows' milk with mastitis have been investigated. Briefly, plasmid expansion in the field isolates was determined while the patogenity and clonal expansion traits of enterococ strains were also investigated.