The primary objective of this study is to demonstrate the non-inferiority, at the assessment visit (V3 (D10/D14)), in terms of bacteriological efficacy of pristinamycin (PRI) administered for 4 days versus amoxicillin (AMX) administered for 6 days in the treatment of tonsillitis caused by GAS, in subjects aged between 6 and 25 in the per protocol (PP) group.