Microbiology Chapter 20 Flashcards

Selective Toxicity and Chemotherapeutic Agents

• Selective toxicity refers to the ability of chemotherapeutic agents to target pathogens without harming the host.
• Ideal agents act specifically against pathogens, minimizing side effects on human cells.

Peptidoglycan Cell Wall Targeting

• Drugs that target bacterial peptidoglycan cell walls are effective since human cells lack this structure.
• Bacteria are particularly vulnerable to these antibiotics, making them a preferred choice.

Polymyxin Usage

• Polymyxin can damage human cell membranes but is safe for external use due to dead outer skin layers.
• Its instability in acidic environments limits oral use.

Mechanism of Action for Quinolones and Fluoroquinolones

• These antibiotics specifically target DNA gyrase, an essential enzyme in bacterial DNA replication.

Challenges in Viral Infection Treatment

• Finding effective antiviral agents is challenging due to viruses using host cellular machinery for replication.
• Selective targeting of viral processes without affecting the host remains complex.

Penicillin G Effectiveness

• Penicillin G is particularly effective against gram-positive bacteria, making it a common treatment choice for infections caused by these organisms.

MRSA Resistance Mechanism

• Methicillin-resistant Staphylococcus aureus (MRSA) has modified its target molecule to resist methicillin, rather than degrading or pumping it out.

Viral Reproduction Dependence

• Viruses rely on host cellular processes for their reproduction, complicating treatment strategies.

Antibiotic Resistance Mechanisms

• Resistance can involve bacterial enzymes that inactivate drugs or modified porins preventing entry.
• Efflux pumps, which expel antibiotics, contribute to resistance by allowing bacteria to survive despite exposure.

Specificity in Enzyme Resistance

• Bacteria resistant to sulfonamide possess enzymes with a higher affinity for PABA, competing effectively with the drug.

Penicillin Resistance Limitations

• Efflux pumps do not aid in penicillin resistance due to the drug's mode of action affecting the cell wall outside the cell membrane.

Role of Membrane Transport Proteins

• Antibiotic resistance through efflux pumps, beta-lactamases, and modified porins requires transport proteins for effective function.

Defining Bacterial Resistance

• Bacterial resistance indicates that the antibiotic no longer kills or inhibits the growth of the bacteria.

Effects of Antibiotic Treatment

• Antibiotics eliminate sensitive bacteria, leading to a selection of those that are resistant.

Gene Transfer in Antibiotic Resistance

• Transduction refers to the process where bacteriophages help transfer antibiotic resistance genes between bacteria.

Mutation Types and Resistance

• Silent mutations do not result in antibiotic resistance, while others, like missense and nonsense mutations, can.

R-Plasmid Acquisition

• Bacterial conjugation is the primary method by which R-plasmids, conferring resistance, are acquired among bacteria.

Synergism in Antibiotic Interaction

• When two antibiotics, such as penicillin and streptomycin, show greater effectiveness together than separately, it exemplifies synergism.

Specific Antibiotic Actions

• Ethambutol selectively targets the tuberculosis-causing bacillus by inhibiting mycolic acid synthesis.
• Drug resistance often arises when antibiotics are used indiscriminately.

Misconceptions About Drug Resistance

• Drug resistance is not exclusive to gram-negative bacteria; it can occur in various bacterial strains.

Susceptibility Indicators

• Natural penicillin is notably effective against Streptococcus pyogenes, making it a go-to treatment.

Broad-Spectrum Antibiotics

• Tetracyclines are recognized for having one of the widest spectra of antimicrobial activity.

Natural Antibiotic Production

• Most natural antibiotics are produced by bacteria, particularly from the genus Streptomyces.

Antibiotic Efficacy

• Polymyxin is specifically effective against gram-negative bacteria, while penicillin has fewer side effects.

Comparison of Penicillin Forms

• Both semisynthetic and natural penicillins share a foundation in β-lactam structure.

Significance of Penicillin

• Although considered a "miracle drug," penicillin was not the first antibiotic; its selective toxicity and impact on bacterium growth are why it is so valued.

Testing for Microbial Susceptibility

• The Kirby-Bauer test does not differentiate between bacteriostatic and bactericidal effects, serving primarily as a susceptibility indicator along with broth dilution tests for MIC and MBC determination.

Test your knowledge with these flashcards covering key concepts from Chapter 20 of Mastering Microbiology. The focus includes principles of selective toxicity and the action of chemotherapeutic agents. Perfect for reinforcing your understanding of microbiological principles.