Highly Variable Penicillin Resistance Determinants PBP 2x, PBP 2b, and PBP 1a in Isolates of Two Streptococcus pneumoniae Clonal Groups, Poland ^23F -16 and Poland ^6B -20

Abstract

Penicillin-binding proteins (PBPs) in representatives of two Streptococcus pneumoniae clonal groups that are prevalent in Poland, Poland 23F -16 and Poland 6B -20, were investigated by PBP profile analysis, antibody reactivity pattern analysis, and DNA sequence analysis of the transpeptidase (TP) domain-encoding regions of the pbp2x, pbp2b, and pbp1a genes. The isolates differed in their MICs of ␤-lactam antibiotics. The majority of the 6B isolates were intermediately susceptible to penicillin (penicillin MICs, 0.12 to 0.5 g/ml), whereas all 23F isolates were penicillin resistant (MICs, >2 g/ml). The 6B isolates investigated had the same sequence type (ST), determined by multilocus sequence typing, as the Poland 6B -20 reference strain (ST315), but in the 23F group, isolates with three distinct single-locus variants (SLVs) in the ddl gene (ST173, ST272, and ST1506) were included. None of the isolates showed an identical PBP profile after labeling with Bocillin FL and sodium dodecyl sulfate-polyacrylamide gel electrophoresis, and only one pair of 6B isolates and one pair of 23F isolates (ST173 and ST272) each contained an identical combination of PBP 2x, PBP 2b, and PBP 1a TP domains. Some 23F isolates contained PBP 3 with an apparently higher electrophoretic mobility, and this feature also did not correlate with their STs. The data document a highly variable pool of PBP genes as a result of multiple gene transfer and recombination events within and between different clonal groups.Streptococcus pneumoniae (the pneumococcus) is a common cause of pneumonia, bacteremia, meningitis, otitis media, and sinusitis; and ␤-lactam antibiotics, especially penicillins, are the most important drugs in the treatment of these infections. Therefore, the emergence and rapid spread of penicillin-nonsusceptible S. pneumoniae (PNSP) represent a serious public health problem. Resistance to ␤-lactams in S. pneumoniae arises from alterations in penicillin-binding proteins (PBPs), which are enzymes involved in bacterial cell wall biosynthesis (16). Of the six PBPs, modifications of PBP 2x, PBP 2b, and PBP 1a which result in their decreased affinity for ␤-lactams are mainly responsible for penicillin resistance in clinical isolates (3). PBP 2x and PBP 2b are primary resistance determinants, and their rearrangements confer low-level resistance (19). The presence of a low-affinity PBP 1a is essential for high-level resistance but requires a modified PBP 2b and/or PBP 2x (33, 38). Since the expanded-spectrum cephalosporins do not interact with PBP 2b (22), only PBP 2x and PBP 1a play a role in resistance to these compounds (33).The PBP-mediated resistance in S. pneumoniae is the result of intra-and interspecies gene transfer events involving related commensal species, such as Streptococcus mitis and Streptococcus oralis (10,11,27,28). This is apparent by the mosaic structure of the PBP genes in resistant isolates, which contain sequence blocks that differ from those in susceptible isolates by approximately 20%, corresponding to about 10% dif...

Penicillin-Binding Protein Gene Alterations in Streptococcus uberis Isolates Presenting Decreased Susceptibility to Penicillin

“…This high conservation between mutations from unrelated isolates (laboratory and environmental strains from diverse origins) seems to be specific to S. uberis. Indeed, in pneumococci, as in other Streptococcus spp., high-level MICs of penicillin are generated by a diversity of different patterns of mutations (6,13,16,21). This specificity of S. uberis might argue for a strong pressure of selection on very precise regions of the protein and probably represents a quasiobligatory pathway for the development of decreased susceptibility to penicillin in this particular species.…”

Characterization of Mutants Deficient in the l,d -Carboxypeptidase (DacB) and WalRK (VicRK) Regulon, Involved in Peptidoglycan Maturation of Streptococcus pneumoniae Serotype 2 Strain D39

“…The peptidoglycan (PG) is an important component of the cell surface of all bacteria (reviewed in references 8, 61, 65-67, and 73) and is the target for several antibiotics, including ␤-lactam antibiotics and vancomycin, used to treat pneumococcal infections (55,68). Notably, resistance of S. pneumoniae to ␤-lactam antibiotics is increasing at an alarming rate due to multiple amino acid changes in the pneumococcal penicillin binding proteins (PBPs) (13,23,33,36,72).…”

Expansion and Evolution of the Streptococcus pneumoniae Spain 9V -ST156 Clonal Complex in Poland

“…The resulting RFLP patterns were compared with those obtained for the reference strain Spain 9V -ST156 (ATCC 700671). Selected pbp genes were sequenced as described in a previous study (27). A part of the murM gene was amplified and sequenced as described by Filipe et al (19).…”