Bacterial growth competing

A closer look at these events reveals that bacteria synthesize folic acid using several enzymes, including one called dihydropteroate synthetase, which catalyzes the attachment of p-aminobenzoic acid to a pteridine ring system. When sulfanilamide is present it competes with the p-amino-benzoic acid (note the structural similarity) for the active site on the enzyme. This activity makes it a competitive inhibitor. Once this site is occupied on the enzyme, folic acid synthesis stops and bacterial growth stops. Folic acid can also be synthesized in the laboratory. ... 

The action of sidfa drugs on bacteria is another example of competitive enzyme inhibition. Fohc acid, a substance needed for growth by some disease-causing bacteria, is normally synthesized within the bacteria by a chemical process that requires p-aminobenzoic acid. Because sulfanilamide, the first sulfa drug, resembles p-aminobenzoic acid and competes with it for the active site of the bacterial enzyme involved, it can prevent bacterial growth (see I Figure 10.10). This is possible because the enzyme binds readily to either of these... 

Early in the development of sulfa drugs as antibiotics, it was found that p-aminobenzoic acid (PABA, 2), which is now used in sunscreens and sunblocks, inhibits the antibacterial action of sulfanilamide. Since p-aminobenzoic acid and sulfanilamide are structurally similar, this discovery led to the speculation that the two compounds competed with each other in some biological process that was essential for bacterial growth. This speculation was eventually supported by experimentation. p-Aminobenzoic acid is used by bacteria in the synthesis of the essential enzyme cofactor folic acid (3). When sulfanilamide is present, it successfully competes with p-aminobenzoic acid for the active site in the enzyme that... 

Following the introduction of the sulphonamides in clinical use, the antibacterial activity was found to be inhibited by the presence of pus. This inhibitory effect of pus was found to be due to the presence of the stmcturally similar p-aminobenzoic acid (PABA) a compound which is also present in folic acid. This led to the observation that the sulphonamides competed with PABA, leading to the dismption of folate synthesis and cessation of bacterial growth. The importance of the sulphonamides in... 

Colicins are pore-forming proteins, produced by certain strains of E. coli, that kill or inhibit the growth of other, competing bacteria and even other strains of E. coli (a process known as allelopathy). Channel-forming colicins are released as soluble monomers. Upon encountering a host cell, the colicin molecule traverses the bacterial outer membrane and periplasm, then inserts itself... 

The body possesses a normal bacterial flora which, by competing for essential nutrients or by the production of inhibitoiy substances such as monolactams or colicins, suppresses the growth of many potential pathogens. 

Given this structural similarity, it should not be surprising to learn that sulfanilamide competes with p-aminobenzoic acid for a binding site on the surface of dihydropteroate synthetase. Put another way, sulfanilamide binds to the enzyme where p-aminobenzoic acid should bind but no reaction occurs. The consequence is that a step in folic acid biosynthesis is disrupted and the bacterial cell is deprived of adequate folic acid. Nucleic acid synthesis, among other things, is disrupted, leading to a cessation of cell growth and division. The human immune system can mop up what remains. No similar consequences befall the human host since it cannot make folic acid in the first place and must get an adequate supply of this vitamin in the diet. 

Table 1.1). Out of the 400 distinct bacterial species in the colon, 30% of fecal isolates are of the genus Bacteroides. This phylogenetic group is characterized by a relatively high growth yield even at low rates, which enables it to compete successfully in this region of the intestine... 

Cdt is composed of three proteins, all encoded by the cdt operon. Two of these proteins bind to human cell membranes where they facilitate the translocation of the third subunit, a SHEP-like phosphatase PI-3,4,5-triphosphate 5-phosphatase. This bacterial phosphatase passes through the membrane and removes the 5-phosphate from PI-3,4,5-triphosphate, causing stimulated lymphocytes and macrophages to undergo apoptosis instead of growth. In nonleukocytic cells such as epidermal cells or fibroblasts, PI-3,4,5-phosphatase is exposed to PTEN, which is 10 times more active on PI-3,4,5-triphosphate than Cdt. The S I I IP-1 ike bacterial enzyme therefore cannot compete with PTEN. The sensitivity of nonleukocytic cells to Cdt is much less than that of stimulated lymphocytes and macrophages. 

A complex interplay of host and pathogen factors influences the acquisition and development of fungal infections. Intact skin or mucosal surfaces serve as primary barriers to infection. Desiccation, epithelial cell turnover, fatty acid content, and low pH of the skin are believed to be important factors in host resistance. Bacterial flora of the skin and mucous membranes compete with fungi for growth. Alterations in the balance of normal flora caused by the use of antibiotics or alterations in nutritional status can allow the proliferation of fungi such as Candida, increasing the likelihood of systemic invasion and infection. ... 

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