Examples of Plasmids

1. Antibiotic resistance genes (enzymes that modify or degrade antibiotics) -- plasmids with these genes are called R factors
2. Heavy metal resistance (enzymes that detoxify metals by redox reactions)
3. Growth on unusual substrates (enzymes for hydrocarbon degradation, etc.)
4. Restriction/modification enzymes (protect DNA, degrade unprotected DNA)
5. Bacteriocins (proteins toxic to other bacteria lacking the same plasmid)
6. Toxins (proteins toxic to other organisms; e.g. humans) -- called virulence plasmids. Some Examples:
   • Staph aureus virulence factors: coagulase, hemolysin, enterotoxin, others
   • pathogenic E. coli strains: hemolysin, enterotoxin
7. Proteins that mediate plasmid transfer to uninfected strains