Rapid screening for penicillin susceptibility of systemic pneumococcal isolates by restriction enzyme profiling of the pbp2B gene.

Restriction digest profiling of pneumococcal pbp2b-specific amplicons was effective for screening penicillin resistance. The pbp2b amplicon of all pneumococcal isolates for which the MICs of penicillin were < or = 0.03 microgram/ml had one of two different susceptible restriction profiles, and all 33 isolates for which MICs were 0.5 microgram/ml or greater had one of seven distinct resistant profiles. Low-concentration penicillin resistance (MICs = 0.06 microgram/ml to 0.25 microgram/ml) was associated with sensitive HaeIII profiles in some isolates; however, RsaI profiling and pbp2b sequence analysis of such isolates revealed that some isolates contained low-level resistant pbp2b alleles, while others had susceptible pbp2b alleles. This data indicates that low-level penicillin resistance is sometimes conferred by determinants other than pbp2b.