Multiplex PCR amplification of penicillin-nonsusceptible pneumococcal isolates. Lanes 1 and 2 are penicillin-susceptible strains. Lanes 3 to 14 are penicillin-nonsusceptible strains. Lanes: M, 100-bp ladder marker; 1, R6 (reference strain); 2, J23 (penicillin-susceptible strain); 3, J3 (group I); 4, J82 (group I); 5, J43 (group III); 6, J80 (group III); 7, J25 (group IV); 8, J46 (group IV); 9, J42 (group V); 10, J64 (group V); 11, J60 (group VI); 12, J86 (group VI); 13, J72 (group II); 14, J73 (group II).