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Title: What is the specific mode of action and the target organisms of each of the three antibiotics? Post by: kyrbi on Sep 22, 2010 What is the specific mode of action and the target organisms of each of the three antibiotics? plate cultures of E.coli, Bacillus cereus and Staphylococcus aureus are used. ???
a. ampicillin b. polymyxin c. streptomycin THANKS and GOD BLESS ;D Title: What is the specific mode of action and the target organisms of each of the three antibiotics? Post by: bio_man on Sep 22, 2010 Streptomycin aka AMINOGLYCOSIDES: The aminoglycosides are a group of antibiotics of complex chemical structure, resembling each other in antimicrobial activity, pharmacokinetic characteristics and toxicity. The main agents are gentamicin, streptomycin, amikacin, tobramycin, netilmicin and neomycin.
Mechanism of action Aminoglycosides inhibit bacterial protein synthesis. Their penetration through the cell membrane of the bacterium depends partly on oxygen-dependent active transport by a polyamine carrier system, and they have minimal action against anaerobic organisms. Chloramphenicol blocks this transport system. The effect of the aminoglycosides is bactericidal and is enhanced by agents that interfere with cell wall synthesis. In paraticular, streptomycin is a protein synthesis inhibitor. It binds to the S12 Protein of the 30S subunit of the bacterial ribosome, interfering with the binding of formyl-methionyl-tRNA to the 30S subunit. This prevents initiation of protein synthesis and leads to death of microbial cells. Humans have structurally different ribosomes from bacteria, thereby allowing the selectivity of this antibiotic for bacteria. However at low concentrations Streptomycin only inhibits growth of the bacteria by inducing prokaryotic ribosomes to misread mRNA. Streptomycin is an antibiotic that inhibits both gram positive and gram negative bacteria, and is a therefore a useful broad spectrum antibiotic. Resistance Resistance to aminoglycosides is becoming a problem. It occurs through several different mechanisms, the most important being inactivation by microbial enzymes, of which nine or more are known. Amikacin was purposefully designed as a poor substrate for these enzymes, but some organisms have developed enzymes that inactivate this agent as well. Resistance as a result of failure of penetration can be largely overcome by the concomitant use of penicillin and/or vancomycin. Antibacterial spectrum The aminoglycosides are effective against many aerobic Gram-negative and some Gram-positive organisms. They are most widely used against Gram-negative enteric organisms and in sepsis. They may be given together with a penicillin in streptococcocal infections caused by Listeria sp. and P. aeruginosa. Gentamicin is the aminoglycoside most commonly used, although tobramycin is the preferred member of this group for P. aeruginosa infections. Amikacin has the widest antimicrobial spectrum and, along with netilmicin, can be effective in infections with organisms resistant to gentamicin and tobramycin. Pharmacokinetic aspects The aminoglycosides are polycations and therefore highly polar. They are not absorbed from the gastrointestinal tract and are usually given intramuscularly or intravenously. They cross the placenta but do not cross the blood-brain barrier, penetrate into the vitreous humour of the eye or into most other secretions or body fluids, although high concentrations can be attained in joint and pleural fluids. The plasma half-life is 2-3 hours. Elimination is virtually entirely by glomerular filtration in the kidney, 50-60% of a dose being excreted unchanged within 24 hours. If renal function is impaired, accumulation occurs rapidly, with a resultant increase in those toxic effects (such as ototoxicity and nephrotoxicity; see below) that are dose-related. Unwanted effects Serious, dose-related toxic effects, which may increase as treatment proceeds, can occur with the aminoglycosides, the main hazards being ototoxicity and nephrotoxicity. Title: What is the specific mode of action and the target organisms of each of the three antibiotics? Post by: bio_man on Sep 22, 2010 I found an amazing article on ampicillin's effect on e.coli
See attachment Title: What is the specific mode of action and the target organisms of each of the three antibiotics? Post by: bio_man on Sep 22, 2010 Polymyxins are antibiotics with a general structure consisting of a cyclic peptide with a long hydrophobic tail. They disrupt the structure of the bacterial cell membrane by interacting with its phospholipids. They are selectively toxic for Gram-negative bacteria due to their specificity for the lipopolysaccharide molecule that exists within many Gram-negative outer membranes.
Staphylococcus species are gram-positive Bacillus cereus is gram-positive Polymyxins, therefore, ARE affective against E. coli because it is gram-negative This is how you are to approach these problems! :) |