BacterialPathways - Beta-Lactam Antibiotics

In Bacillus licheniformis and Staphylococcus aureus, a membrane-bound penicillin receptor (BlaR/MecR) detects the presence of beta-lactam and launches a cytoplasmic signal leading to the inactivation of BlaI/MecI repressor, and the synthesis of a beta-lactamase or a low affinity target.

Fig. 5: Beta-Lactam Rings of Penicillins, Cephalosporins, Imipenem, and Clavulanate

Interference with this process results in the formation of a weak cell wall and osmotic lysis of the bacterium. Agents that inhibit peptidoglycan synthesis include the penicillins (penicillin G, methicillin, oxacillin, ampicillin, amoxicillin, ticarcillin, etc.), the cephalosporins (cephalothin, cefazolin, cefoxitin, cefotaxime, cefaclor, cefoperazone, cefixime, ceftriaxone, cefuroxime, etc.), the carbapenems (imipenem, metropenem), the monobactems (aztreonem), and the carbacephems (loracarbef). Penicillins, monobactams, carbapenems, and cephalosporins are known chemically as beta-lactam antibiotics because they all share a molecular structure called a beta-lactam ring (see Fig. 5). The glycopeptides (vancomycin, teichoplanin) and lipopeptides (daptomycin) also inhibit peptidoglycan synthesis.


Beta-Lactam Antibiotics; Beta ..

Flash animation illustrating how penicillins inhibit peptidoglycan synthesis.

Some bacteria produce various beta-lactamases, enzymes that break the beta-lactam ring at the site indicated by the arrows, and are able to inactivate some forms of these drugs.


Inhibition of cell wall synthesis enzymes

Penicillins, monobactams, carbapenems, imipenems, and cephalosporins are known chemically as beta-lactam antibiotics because as part of their chemical structure they contain what is know as a beta-lactam ring. The above illustration shows the basic structure of penicillin, cephalosporin, imipenem, and clavulanate. "R" represents sites where different chemical side chains attach, depending on the particular antibiotic.

inhibit peptidoglycan synthesis in the cell wall.

Penicillins, cephalosporins, as well as other beta-lactam antibiotics, bind to the transpeptidase enzymes (also called penicillin-binding proteins) responsible for reforming the peptide cross-links between rows and layers of peptidoglycan of the cell wall as new peptidoglycan monomers are added during bacterial cell growth. This binding blocks the transpeptidase enzymes from cross-linking the sugar chains and results in a weak cell wall. In addition, these antibiotics appear to interfere with the bacterial controls that keep autolysins in check, with resulting degradation of the peptidoglycan and osmotic lysis of the bacterium (see Fig. 6).

List of antibiotics - Wikipedia

Glycopeptides, such as the antibiotic vancomycin,inhibit both transglycosylation and transpeptidationreactions during peptidoglycan assembly. They bind to the muropeptidesubunit as it is transferred out of the cell cytoplasm and inhibitsubsequent polymerization reactions. Vancomycin is not effectiveagainst Gram-negative bacteria because it cannot penetrate their outermembrane. However, it has become important in clinical usage fortreatment of infections by strains of that are resistant to virtually all other antibiotics (MRSA).

The following is a list of antibiotics

Most antibiotics in clinicalusage are directedagainst bacterial cell wall synthesis, bacterial protein synthesis, orbacterialnucleic acid synthesis, which are unique in some ways tobacteria. For example, the beta lactam antibiotics (penicillin and its relatives)inhibit peptidoglycan synthesis in the cell wall.