Bacteria peptidoglycan

Glycoproteins will be discussed in some detail in Section 12.4. The carbohydrate components of proteoglycans are known as glycosaminoglycans. Proteoglycans are essential parts of the connective tissue In mammals and are also present to some extent in fish and bacteria (peptidoglycans from the cell wall of bacteria are different biopolymers and were discussed in Section 7.9). The term mucopolysaccharide was used in the past to describe polysaccharide materials of animal origin containing 2-amino-2-deoxyhexoses. 

Peptidoglycans have been postulated as a possible causative agent for pulmonary inflammation associated with inhalation of Gm+ bacteria. Peptidoglycans are components of the cell wall envelope of bacteria and are especially prevalent in the backbone of Gm+ bacteria. They may act as endotoxin-like molecules when inhaled. Muramic acid is an amino sugar component of peptidoglycans that does not appear elsewhere in nature and is a suitable marker for analytical assays (Black et al., 1994 Fox et al., 1993 Fox et al., 1995 Sonesson et al., 1988). Although peptidoglycans have been found in hospital and home air conditioner filters (Fox and Rosario, 1994), to date there have been no systematic dose-response studies to identify their potency. 

Cell wall Peptidoglycan a rigid framework of polysaccharide cross-linked by short peptide chains. Some bacteria possess a lipopolysaccharide- and protein-rich outer membrane. Mechanical support, shape, and protection against swelling in hypotonic media. The cell wall is a porous nonselective barrier that allows most small molecules to pass. 

FIGURE 9.25 Teichoic acids are covalently linked to the peptidoglycan of Grampositive bacteria. These polymers of (a, b) glycerol phosphate or (c) ribitol phosphate are linked by phosphodiester bonds. 

Penicillin has an interesting mode of action it prevents the cross-linking of small peptide chains in peptidoglycan, the main cell wall polymer of bacteria. Pre-existing cells are unaffected, but all newly produced cells are abnormally grown. The newborn cells are unable to maintain their wall rigidity, and they are susceptible to osmotic lysis. 

Lactam antibiotics are bicyclic or monocyclic azetidinone ring-containing compounds (Fig. 1). They kill bacteria by preventing the assembly of (4-3) peptidoglycans. These covalently closed net-like polymers form the matrix of the cell wall by which the bacteria can divide and multiply, despite their high internal osmotic pressure. 

Vancomycin is bactericidal to most susceptible bacteria at concentrations near its minimum inhibitory concentration (MIC) and is an inhibitor of bacterial cell wall peptidoglycan synthesis, although at a site different from that of j3-lactam antibiotics (Chapter 9). 

Catechins Bacteria Cell wall peptidoglycan 8-lactams Inhibition of penicillinase activity [67]... 

C. trachomatis possesses characteristics resembling both bacteria and viruses. Its major membrane is comparable to that of gram-negative bacteria, although it lacks a peptidoglycan cell wall and requires cellular components from the host for replication. Chlamydia transmission risk is thought to be less than that of gonorrhea. 

Mode of action Interferes with bacterial cell wall synthesis during active multiplication, causing cell wall death and resultant bactericidal activity Inhibits bacterial cell wall synthesis by binding to one or more of the penicillin-binding proteins, which in turn inhibit the final transpeptidation step of peptidoglycan synthesis in bacterial cell walls bacteria usually lyse from ongoing autolytic enzyme activity... 

We might also note another important difference between animal and bacterial cells. Bacterial cells have rigid cell walls containing peptidoglycan and associated substances. Animal cells, on the other hand, lack cell walls. This difference is important for the way by which the virus genome enters and exits the cell. In bacteria, the protein coat of the virus remains on the outside of the cell and only the nucleic acid enters. In animal viruses, on the other hand, uptake of the virus often occurs by endocytosis (pinocytosis or phagocytosis), processes which are characteristic of animal cells, so that the whole virus particle enters the cell. The separation of animal virus genomes from their protein coats then occurs inside the cell. 

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