STREPTOGRAMINS:

• These are novel class of antibiotics which act by inhibiting protein synthesis
• Important members of this group include streptogramin, virginiamycin, pristinamycin and quinopristinl daflopristin.
• These family of antibiotics consists of two distinct groups: group A and group B antibiotics. Members of group A contain 23-membered unsaturated ring with lactone and peptide bonds while group B antibiotics are dispeptides.

Mechanism of action:

• Streptogramin A and B antibiotics are bacteriostatic however when used in conjunction with one another becomes bactericidal.

Streptogramin A binds to peptidyl transferase domain of 50S ribosomal subunit

Prevents the elongation of peptide chain

Release of incomplete peptides

Virginiamycin:

• It is streptogramin antibiotics obtained from Streptomyces virginae
• It is combination of two separate antibiotics named virginiamycin S & M in ratio 1:4.
• Individually both fractions of virginiamycin have mild bacteriostatic action, but when combined together they produce synergistic bactericidal activity.
• It is active against gram +ve organism with mild toxoplasmosis activity.
• It is mostly used as growth promoter and production enhancer in swine and poultry ration.
• It is also used to treat swine dysentery.