Effects of amino acid alterations in penicillin-binding proteins (PBPs) 1 a, 2 b, and 2x on PBP affinities of penicillin, ampicillin, amoxicillin, cefditoren, cefuroxime, cefprozil, and cefaclor in 18 clinical isolates of penicillin-susceptible, -intermediate, and -resistant Pneumococci - Nagai, K; Davies, TA; Jacobs, MR; Appelbaum, PC (Antimicrob Agents Chemother., 2002)