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Category: Bacterial Pathogenesis
Resistance Mediated by Penicillin-Binding Proteins, Page 1 of 2
< Previous page | Next page > /docserver/preview/fulltext/10.1128/9781555815615/9781555813031_Chap07-1.gif /docserver/preview/fulltext/10.1128/9781555815615/9781555813031_Chap07-2.gifAbstract:
The transpeptidases are members of the family of penicillin-binding proteins (PBPs), which have become known as the targets of β-lactam antibiotics. PBPs perform a variety of critical functions for the bacterial cell. PBPs are found in all pathogenic bacteria except those of the genus Mycoplasma, which do not have a cell wall. Reduced expression of PBP2 (type B, assignment not certain) is one of the most frequently observed mechanisms of resistance to carbapenems. PBP2 (type B4) and PBP3 (type B5) have been specifically implicated in resistance towards β-lactams. Increased expression of PBP4 (type C2) has been implicated in resistance to both β-lactams and glycopeptides. Hakenbeck et al. implicated the D,D-carboxypeptidase S. pneumoniae PBP3 (type C3) in resistance. PCR-based methods for the detection of antibiotic resistance are becoming increasingly important with the expanding use of molecular techniques for bacteriological diagnosis. Antibody-based tests have also been investigated for detection of methicillin resistance in staphylococci. There are several experimental β-lactams now known to be potent inhibitors of the staphylococcal type B1 PBP that is the primary determinant of β-lactam resistance in these organisms, of which ceftobiprole is the most advanced in clinical development. An understanding of the mechanism of methicillin resistance has led to the discovery of accessory factors that influence the level and nature of methicillin resistance.
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Comparison of PBP profiles of selected organisms and pattern alterations commonly encountered in resistant organisms. The PBPs have been labeled by incubation of membranes derived by sonication of cultures of the indicated organisms with radiolabeled benzylpenicillin and then resolution of the proteins by standard sodium dodecyl sulfate-polyacrylamide gel electrophoresis. From left to right:E. coli, MRSA, Streptococcus pneumoniae, penicillin susceptible (PenS) and an example of a penicillin-resistant (PenR) isolate where loss of affinity makes some PBPs disappear, and Enterococcus faecium, ampicillin-susceptible (AmpS) and an example of an ampicillin-resistant (AmpR) isolate where loss of affinity of PBP1 and PBP4 as well as overexpression of PBP5 are evident.
Location of mutations in PBPs conferring resistance to β-lactams. Regions from the sequences of susceptible proteins are shown, with the residues that are mutated in resistant isolates shown in bold and boxed. The highly conserved residues that comprise parts of the active site ( 38 , 39 ) are shown in bold. The organisms denoted are E. faecium (Efc), H. influenzae (Hin), H. pylori (Hpy), N. meningitidis (Nme), S. aureus (Sau), and S. pneumoniae (Spn).
Comparison of the PBPs in E. coli, P. aeruginosa, S. aureus, S. pneumoniae, and E. faecalis a
Comparison of susceptibilities of the PBPs of E. coli and S. aureus to different β-lactam classes
Distribution of PBP types among the bacteria and their contribution to β-lactam resistance a
Kinetic parameters describing the reaction of soluble constructs of PBPs
Representative anti-MRSA cephalosporins
Anti-MRSA carbapenems
Modulators of PBP2′-mediated resistance in staphylococci