Streptogramins are a class of bacteriocidal antibiotics. They are a combination of quinupristin and dalfopristin in a 30:70 ratio. The interaction of these components is greater than the individual reactions. Quinupristin prevents elongation of the 50S ribosomal subunit while dalfopristin changes the structure of the 50S subunit to promote more favourable binding with quinupristin in a synergistic reaction, effectively inhibiting protein synthesis. Virginiamycin is an antibiotic similar to pristinamycin. It is used to prevent microbial contamination in fuel ethanol industries which act as an alternative to traditional oil based fuel sources.