Peritonsillar abscess is most commonly caused by

Peritonsillar abscess ( Quinsy) is the collection of pus in the peritonsillar space which lies between the capsule of tonsil and superior constrictor muscle. A peritonsillar abscess usually follows acute tonsillitis. First crystal Magna is infected and sealed off. Culture of pus from the abscess May reveal beta-hemolytic streptococci, S.aureus, or anaerobic organisms. (Ref: Diseases of ENT, PL Dhingra, 7th edition, pg no.298)