Burton's Microbiology for the Health Sciences PDF

# Burton's Microbiology for the Health Sciences ## Chapter 9. Controlling Microbial Growth _in Vivo_ Using Antimicrobial Agents ### Chapter 9 Outline - Introduction - Characteristics of an Ideal Antimicrobial Agent - How Antimicrobial Agents Work - Antibacterial Agents - Antifungal Agents - Antip...

# Burton's Microbiology for the Health Sciences ## Chapter 9. Controlling Microbial Growth _in Vivo_ Using Antimicrobial Agents ### Chapter 9 Outline - Introduction - Characteristics of an Ideal Antimicrobial Agent - How Antimicrobial Agents Work - Antibacterial Agents - Antifungal Agents - Antiprotozoal Agents - Antiviral Agents - Drug Resistance - Some Strategies in the War Against Drug Resistance - Empiric Therapy - Undesirable Effects of Antimicrobial Agents - Concluding Remarks ### Introduction - **Chemotherapy** is the use of any chemical (_drug_) to treat any disease or condition. - A **chemotherapeutic agent** is any drug used to treat any condition or disease. - An **antimicrobial agent** is any chemical (_drug_) used to treat an infectious disease, either by inhibiting or killing pathogens _in vivo_. Some antimicrobial agents are **antibiotics**. - Drugs used to treat bacterial diseases are called **antibacterial agents**, those used to treat - fungal diseases, **antifungal agents**, - protozoal diseases, **antiprotozoal agents**, - viral diseases, **antiviral agents**. - An **antibiotic** is a substance produced by a microorganism that kills or inhibits growth of other microorganisms. ### Introduction, cont. A visualization of the complexity of antimicrobial treatment is shown. An antimicrobial drug must be effective, but also be able to: - Be retained in the body long enough to have an effect. - Not cause side effects like toxicity or allergies. - Not be eliminated from the body too quickly. - Not be destroyed by the body's defenses. - Be the right drug for the right infection. - Not be eliminated too slowly. - Not be administered in impractical ways (ie, intravenously). - Be able to overcome a possible development of resistance to the drug. - Avoid making a situation worse (ie, an existing illness). ### Penicillin - The discovery of penicillin by Alexander Fleming. - (A) Colonies of _Staphylococcus aureus_ are growing well in this area of the plate. - (B) Colonies are poorly developed in this area of the plate because of an antibiotic (_penicillin_) being produced by a colony of _Penicillium notatum_ (_a mould_), shown at C. ### Characteristics of an Ideal Antimicrobial Agent - The ideal antimicrobial agent should: - Kill or inhibit the growth of pathogens. - Cause no damage to the host. - Cause no allergic reaction in the host. - Be stable when stored in solid or liquid form. - Remain in specific tissues in the body long enough to be effective. - Kill the pathogens before they mutate and become resistant to it. - A table shows a diagram of a bacterial cell with its different targets of antimicrobial agents: - **Cell wall synthesis**: Cycloserine, Bacitracin, Penicillins, Cephalosporins, Monobactams, Carbapenems - **DNA gyrase**: Quinolones, Nalidixic acid, Ciprofloxacin, Novobiocin - **RNA elongation**: Actinomycin - **DNA-directed RNA polymerase**: Rifampin, Streptovaricins - **Protein synthesis (50S inhibitors)**: Erythromycin, Chloramphenicol, Clindamycin, Lincomycin - **Protein synthesis (30S inhibitors)**: Tetracyclines, Spectinomycin, Streptomycin, Gentamicin, Kanamycin, Amikacin, Nitrofurans - **Protein synthesis (tRNA)**: Mupirocin, Puromycin - **Folic acid metabolism**: Trimethoprim, Sulfonamides - **Cytoplasmic membrane structure**: Polymyxins, Daptomycin ### How Antimicrobial Agents Work - The 5 most common mechanisms of action of antimicrobial agents are: - Inhibition of cell wall synthesis - Damage to cell membranes - Inhibition of nucleic acid synthesis (either DNA or RNA synthesis) - Inhibition of protein synthesis - Inhibition of enzyme activity - A diagram shows different targets of antimicrobial agents, including: - Inhibition of cell wall synthesis: Penicillins, Cephalosporins, Vancomycin, Bacitracin, Isoniazid, Ethambutol - Inhibition of pathogen's attachment to, or recognition of, host: Arildone - Inhibition of DNA or RNA synthesis: Actinomycin, Quinolones, Rifampin - Inhibition of general metabolic pathway: Sulfonamides, Trimethoprim - Inhibition of protein synthesis: Aminoglycosides, Tetracyclines, Chloramphenicol, Macrolides - Disruption of cytoplasmic membrane: Polymyxins