Conjugational Plasmid Transmissibility of Virulence-Related and Antibiotic Resistance Genes Among Enterococcal Isolates

Enterococci comprise an important and diverse group of bacteria that cause disease in human and animals. They reside in the gastrointestinal tract of human and animal, soil, water, foods, and can persist in elevated salt contents and various pH values. They can readily acquire antibiotic resistance and various other virulence factors. In this study, the prevalence of various virulence factors among different clinical isolates versus those isolated from healthy individuals was compared. In this analytic cross-sectional study, enterococcal strains isolated from clinical and healthy cases were tested for various virulence related properties such as hemolysin, gelatinase, hemoglutinin, DNase, and fremone(aggregative substance) production. T-test and chi-square test were used for analysis of the data and their antibiotic resistance patterns were also determined. The ability to exchange resident plasmids via conjugation was tested by two different mating protocols. The frequency of gelatinase, aggregation substance, and hemolysin production was higher in E.faecalis relative to those in E.faecium. However, no statistically significant difference was detected in the other trains. Fremone-responsive plasmids were common in most isolates and had the ability to transfer between strains with high frequency(10-4-10-7). Most isolates contained one or more plasmids in the 3-98 MDa range. Two isolates showed total resistance to all of the antibiotics tested. Antibiotic resistance genes had the ability for conjugational inter-strain transfer. The prevalence of aggregative substance in the strains isolated from clinical cases was much higher than those obtained from the control group(P<0.001). Since no known protein ecotoxin was identified in enterococci, their pathogenic potential may be attributed to a variety of extracellular enzymes, antibiotic resistance, aggregative substance, and other factors. Their importance in medicine is related to their ability to acquire antibiotic resistance and cause nosocomial infections in hospitalized and debilitated patients. The statistically significant higher proportion of aggregative substance in enterococci spp, isolated from sick people in comparison with those obtained from healthy cases, points to the pivotal role conjugational gene transfer may play in the acquisition of pathogenic potential.