Examination of several hundred penicillin-resistant clinical isolates of Streptococcus pneumoniae has revealed extensive strain-to-strain variation in the number and molecular size of penicillin-binding proteins (PBPs). This polymorphism has been used to classify resistant isolates into groups (PBP families) that share distinct electrophoretic profiles. We describe herein properties of four such PBP families: two from Spain (and/or Ohio) and one each from Hungary and Alaska. We have discovered that representative isolates assigned to each PBP family also share capsular serotype, antibiotic resistance pattern, pneumococcal surface protein A type, and multilocus enzyme genotype. The results demonstrate independent clonal origin for strains assigned to each PBP family. Each resistant clone occurs with uniquely high incidence within specific geographic areas.

An epidemiologic survey of antibiotic resistance among pneumococcal isolates collected during 1988 and 1989 in Hungary indicated that as many as 58% of all isolates and 70% of isolates from children were resistant to penicillin. These figures surpass even the highest values reported thus far for Spain and South Africa for the same period. Almost or more than 70% of the penicillin-resistant isolates were also resistant to tetracycline, erythromycin, and cotrimoxazole and approximately 30% to chloramphenicol. Intravenous administration of ampicillin (30 mg/kg) did not interfere with the growth in the cerebrospinal fluid of three resistant strains introduced into the rabbit model of experimental meningitis. No resistant strain showed beta-lactamase activity. A representative highly resistant strain contained altered penicillin-binding proteins (low penicillin affinities and abnormal molecular sizes) and was also resistant to the lytic and killing effects of penicillin.

An epidemiological survey of penicillin resistance as determined by minimum inhibitory concentrations (MICs) in Streptococcus pneumoniae strains collected from several Hungarian laboratories in 1988-1989 indicated a prevalence of 58% among a total of 135 isolates. A significantly higher resistance rate (69.2%) was found for isolates from pediatric patients than from adult patients (44.0%). Penicillin-resistant strains were more frequently resistant to non-beta-lactam antibiotics (tetracycline, erythromycin, co-trimoxazole, and chloramphenicol) than were penicillin-sensitive strains. On the basis of the MIC50 and MIC90 values of ampicillin and five cephalosporins for penicillin-resistant strains, it was established that ampicillin and cephalexin were not superior to penicillin. The low MIC90 of ceftriaxone and cefotaxime for these organisms reflects promising therapeutic potential, even in septicemia and meningitis caused by penicillin-resistant strains. The therapeutic alternative to penicillin in the treatment of respiratory tract infection may be second-generation cephalosporins such as cefuroxime or cefamandole.

Altered penicillin-binding proteins (PBPs) with reduced affinity for penicillin are encoded by mosaic genes in penicillin-resistant clinical isolates of Streptococcus pneumoniae. Generally, members of one bacterial clone contain the same mosaic gene. We report here on a serotype 19A clone of penicillin- and multiple-resistant S. pneumoniae prevalent in Hungary, members of which are exceptionally diverse in terms of PBP properties. The pbp2x gene of four 19A isolates was sequenced, and a distinct mosaic structure detected in each case. The pbp2x genes also differed from a homologous gene of a high-level penicillin-resistant S. mitis from Hungary. The contribution of PBPs to resistance development was studied on transformation experiments using the laboratory strain R6 as recipient, and PBP genes from the type 19A isolate Hu11. pbp2x and pbp2b function as primary resistance determinants for different beta-lactams. Secondary transformation with pbp1a increased the resistance level considerably for penicillins and cefotaxime. Chromosomal DNA of a high-level penicillin- and cefotaxime-resistant S. mitis from Hungary also transformed the R6 strain to increased resistance levels, and PBP2x and PBP2b functioned as primary resistance determinants as above. In contrast, high-level cefotaxime resistance appeared to be due to a low affinity PBP2a, indicating that this PBP can also function as a resistance determinant.