Plasmid analysis

Plasmids are small, self-replicating circular DNA found in many bacteria.These often encode genes related to antibiotic resistance and certain virulence factors. In epidemiological studies, relatedness of isolated pathogenic bacterial strains can be determined from the number andsize of plasmids the bacteria carry. Plasmid profile analysis was among the earliest nucleic acid-based techniques applied to the diagnosis of infectious diseases and has proven useful in numerous investigations . This method has also been widely utilized for tracking antimicrobial resistance during nosocomial outbreaks. In studies of the epidemiology of plasmids, analysis of restriction fragments has proved valuable. This technique is widely used to monitor the spread of resistance-encoding plasmids between organisms and between hospitals, communities, or even countries.The weakness of the analysis is inherent in the fact that plasmids are mobile, extrachromosomal elements, not part of the chromosomal genotype. Because plasmids can be spontaneously lost from or readily acquired by a host stain, epidemiologically related isolatescan exhibit different plasmid profiles(van et al., 2007).