"عسى ان تكون علما ينتفع به" Antibiotic groups Virginamycin

1. Antibiotics Groups
Streptogramins

2. Streptogramins Group
 The streptogramins include:
1. Virginiamycin
• It is produced by a mutant strain of Streptomyces virginiae.
• It is a natural mixture of factor M and factor S
• Its antibacterial activity is synergistically optimum when the M:S
ratio is approximately 4 : 1
2. Pristinamycin
• It is a combination of quinupristin (streptogramin B) and
dalfopristin (streptogramin A) in a 30:70 ratio.

3. Mechanism of Action - Spectrum
 Gram positive
 The antibacterial activity of the streptogramins is attributed
to the inhibition of protein synthesis.
1. Virginiamycin bind to 50S ribosomal subunits and inhibiting the
formation of peptide bonds during protein synthesis.
2. Pristinamycin bind to the 50S ribosomal subunit at different sites
located in close proximity, thereby interfering with the formation of
polypeptide chains.

4. Resistance
Pristinamycin
 the mechanisms of resistance to class A streptogramins and
class B streptogramins are different.
– Class A streptogramins, active efflux of drug from the bacterial cell as
well as drug inactivation by acetyltransferases contribute to
resistance.
– Class B streptogramins, the most common, due to methylation of the
target 23S ribosomal RNA, while a less common mechanism involves
enzymatic cleavage of a structural ring in the drug.

5. Indications
Virginiamycin
1. To improve daily live weight gain and feed conversion
efficiency in feedlot and grazing cattle, broilers, turkeys, and
pigs in several countries.
– Banned in the EU in 1999 and in Australia in 2005.
2. In feedlot cattle, it also reduces the incidence and severity of
liver abscessation.
3. To reduces the risk of fermentative lactic acidosis in cattle
and sheep fed high-concentrate diets.
4. To reduce the risk of laminitis in horses on high grain diets.