Pristinamycin, produced by Streptomyces pristinaespiralis, is an orally active streptogramin-like antibiotic consisting of two chemically unrelated components: Pristinamycin I (PI) and Pristinamycin II (PII). Pristinamycin is highly active against many antibiotic-resistant pathogens, particularly Gram-positive bacteria, including Methicillin-resistant Staphylococcus aureus (MRSA), Vancomycin-resistant S. aureus (VRSA) and Enterococcus faecium (VREF).In Vitro: In-vitro studies show pristinamycin to inhibit Staphylococci and Streptococci, including Erythromycin highly-resistant organisms, at a concentration of less than or equal to 0.78 mg/l[2].In Vivo: To study Pristinamycin activity in vivo, mice infected IP with C. psittaci. Mortality in the control group was 70%. Three groups of mice received 25 mg/kg, 50 mg/kg and 100 mg/kg Pristinamycin respectively. The antibiotic was active in the 100 mg/kg dosage which is the therapeutic dosage.