Lecture Notes 6.7 - Antimicrobial Drugs PDF

Lec 6.7  Antimicrobial Drug: is a drug used to treat a microbial infection. Antibiotics: are drugs that kill or inhibit the growth of bacteria and are used to treat bacterial infections. Antibiotics: o Fight pathogens o Interfere with formation of cell walls o Many obtained from bacter...

Lec 6.7  Antimicrobial Drug: is a drug used to treat a microbial infection. Antibiotics: are drugs that kill or inhibit the growth of bacteria and are used to treat bacterial infections. Antibiotics: o Fight pathogens o Interfere with formation of cell walls o Many obtained from bacteria or fungi o Others produced synthetically  History The discovery of the first antibiotic was an accident. In 1928, sir Alexander Fleming, , a Scottish biologist accidentally contaminated a plate with a fungus. He observed a clearly defined region of no bacterial growth where the fungi had contaminated the plate.  Zone of inhibition If an antibiotic stops the bacteria from growing or kills the bacteria, there will be an area around discs. where the bacteria have not grown enough to be visible. This is called a zone of inhibition. What factors affect the size of the zone of inhibition? ▪ Drug diffusion rate through agar. ▪ Drug concentration in the disk. ▪ Type of microorganism. ▪ Type of drug.  Narrow and Broad-Spectrum antibiotics Narrow-spectrum drugs: affect only a select group of microbes, gram-positive cells. (Clarithromycin, Clindamycin, Erythromycin). Advantages : The narrow-spectrum antibiotic will not kill as many of the normal microorganisms in the body as the broad- spectrum antibiotics. So, It has less ability to cause superinfection. ❖ Narrow spectrum antibiotics can be used only if the causative organism is identified.  Broad-spectrum drugs: affect large number of microbes. Azithromycin, Amoxicillin, Vancomycin, Levofloxacin, Streptomycin, Tetracycline, Chloramphenicol. Disadvantages: o Children who receive broad-spectrum antibiotics during their first year of life are at increased risk of developing childhood asthma. o Broad Spectrum antibiotics may give rise to drug resistance.  Antibiotic targets 1. Bacterial cell wall 2. Bacterial plasma membrane 3. Synthesis of bacterial proteins 4. Bacterial nucleic acids 5. Bacterial metabolism  Antibacterial Antibiotics Inhibitors of Cell Wall Synthesis and Injury to plasma membrane: 1. All penicillin contain a b-lactam ring. 2. Natural penicillin produced by Penicillium are effective against gram-positive. - Inhibitors of Protein Synthesis: Aminoglycosides, tetracyclines, chloramphenicol, and macrolides inhibit protein synthesis at 70S ribosomes. - Inhibitors of Nucleic Acid (DNA/RNA) Synthesis 1. Rifamycin inhibits mRNA synthesis; it is used to treat tuberculosis (Mycobacterium tuberculosis). 2. Quinolones and fluoroquinolones inhibit DNA gyrase for treatment of urinary tract infections  How is resistance spread Antibiotic resistance can either be inherent or acquired. ✓ Inherent Resistance: Some bacteria are naturally resistant to certain antibiotics due to their physiological characteristics. ✓ Acquired Resistance: Other bacteria acquire resistance through the transfer of resistance genes or random spontaneous chromosomal mutations.  Mechanisms of Antibiotic Resistance Production of Enzymes: 1. Beta-lactamases: Enzymes that hydrolyze beta-lactam drugs, making the cell resistant to these antibiotics. 2. Aminoglycoside-modifying enzymes: Gram-negative bacteria produce enzymes that modify aminoglycosides, rendering them inactive. 3. Chloramphenicol acetyl transferase: Gram-negative bacteria produce an acetyl transferase that modifies chloramphenicol, making it inactive. Mutation: Alteration of PBPs in both gram-positive and gram-negative bacteria prevents beta-lactams from binding, leading to resistance. Efflux Pumps: A variety of efflux pumps in both gram-positive and gram-negative bacteria provide antimicrobial resistance.  Allergy testing skin Are used to find out which substances cause a person to have an allergic reaction. Such as skin prick test and batch test.  Antifungal Drugs is used to treat and prevent mycoses and infections. Antifungals Group Medication 1. Polyenes 2. Imidazole 3. Triazole 4. Allylamines 5. Inhibitors  Antiretroviral drugs are classified into five groups, each targeting a specific viral process: 1. NRTIs (Nucleoside/Nucleotide Reverse Transcriptase Inhibitors) 2. NNRTIs (Non-Nucleoside Reverse Transcriptase Inhibitors) 3. Protease Inhibitors 4. Entry Inhibitors 5. Integrase Inhibitors Antiprotozoan and Antihelminthic Drugs Chloroquine and quinacrine stop DNA synthesis by intercalation between base pairs. metronidazole(is an antibiotic that is used to treat a wide variety of infections. It works by stopping the growth of certain bacteria and parasites.) Antihelminthic drugs include niclosamide( is effective against cestodes that infect humans and many other animals.),