Chapter 12 – Antimicrobial Treatment (Microbiology: A Systems Approach, 7e)

These 70 Question-and-Answer flashcards cover the key terminology, mechanisms, drug classes, testing methods, resistance concepts, and clinical considerations presented in Chapter 12 on antimicrobial treatment.

What is the main goal of antimicrobial chemotherapy?

To administer a drug that destroys the infective agent without harming the host’s cells.

What two major natural sources provide most antibiotics?

Bacteria (especially Streptomyces and Bacillus) and fungi (Penicillium and Cephalosporium).

Name two common laboratory methods for testing antimicrobial susceptibility.

Kirby–Bauer disc diffusion test and tube dilution (MIC) test.

What does MIC stand for, and what does it measure?

Minimum Inhibitory Concentration; the smallest concentration of a drug that visibly inhibits microbial growth.

Define therapeutic index (TI).

The ratio of the drug dose that is toxic to humans to the dose that is therapeutically effective; a higher TI is safer.

Define selective toxicity.

Ability of a drug to kill or inhibit microbes without damaging host tissues.

Which drugs have excellent selective toxicity and why?

β-lactam drugs such as penicillins, because they target bacterial cell-wall synthesis, a structure absent in human cells.

List the five major targets of antimicrobial agents.

1) Cell-wall synthesis, 2) Nucleic acid structure/function, 3) Protein synthesis (ribosomes), 4) Cell-membrane structure/function, 5) Folic-acid (metabolic) pathways.

Differentiate between microbicidal and microbiostatic drugs.

Microbicidal drugs kill microbes outright; microbiostatic drugs merely inhibit their growth.

Define prophylaxis in antimicrobial therapy.

Use of a drug to prevent an imminent infection in a person at risk.

What is the difference between broad-spectrum and narrow-spectrum antimicrobials?

Broad-spectrum drugs act against a wide variety of microbes; narrow-spectrum drugs target a specific group.

Give one example each of a broad- and a narrow-spectrum antibiotic.

Broad-spectrum: tetracycline. Narrow-spectrum: polymyxin or penicillin G.

What is an antibiogram?

A profile of antimicrobial sensitivity of a specific microorganism obtained from susceptibility testing.

Which test uses a plastic strip with a gradient of antibiotic concentrations to determine MIC directly on an agar plate?

The Etest.

Name three patient factors that must be considered before prescribing an antimicrobial.

Allergies, liver or kidney function, pregnancy/age (e.g., infants or elderly).

What structural feature defines the β-lactam class of antibiotics?

The presence of a β-lactam ring in their chemical structure.

List the three structural components of a penicillin molecule.

Thiazolidine ring, β-lactam ring, and variable side chain (R group).

How do β-lactamases (penicillinases) contribute to drug resistance?

They are enzymes that hydrolyze the β-lactam ring, inactivating β-lactam antibiotics.

What compound is often combined with penicillins to inhibit β-lactamase enzymes?

Clavulanic acid.

Name the five generations of cephalosporins in order.

1st: cephalothin/cefazolin; 2nd: cefaclor/cefonicid; 3rd: cephalexin/cefotaxime/ceftriaxone; 4th: cefpirome/cefepime; 5th: ceftobiprole.

Which carbapenem drugs are reserved for severe hospital infections?

Doripenem and imipenem.

What topical antibiotic found in Neosporin targets the cell wall?

Bacitracin.

Which drug is first-line therapy against Mycobacterium tuberculosis during active growth?

Isoniazid (INH).

For MRSA infections resistant to β-lactams, which glycopeptide antibiotic is often used?

Vancomycin.

What is the mechanism of action of aminoglycosides?

They bind the 30S ribosomal subunit causing misreading of mRNA and abnormal proteins.

Give two clinical uses for streptomycin.

Treatment of bubonic plague and tularemia; also used in tuberculosis therapy.

How do tetracyclines inhibit bacterial growth?

They block attachment of tRNA to the A site on the 30S ribosome, halting protein synthesis.

Name two common macrolide antibiotics and one typical infection they treat.

Erythromycin and azithromycin; used for respiratory or skin infections (e.g., otitis media, pharyngitis).

Which synthetic class blocks initiation of protein synthesis and treats MRSA & VRE?

Oxazolidinones (e.g., linezolid).

What metabolic pathway is blocked by sulfonamides and trimethoprim?

Folic acid synthesis via inhibition of tetrahydrofolate-producing enzymes.

How do fluoroquinolones act against bacteria?

They inhibit DNA gyrase and topoisomerase IV, preventing DNA replication.

Which antibiotic inhibits RNA polymerase and is used for tuberculosis and leprosy?

Rifampin (an ansamycin).

Why are polymyxins considered last-resort antibiotics?

They disrupt cell membranes but are nephrotoxic (kidney-damaging).

What lipopeptide antibiotic is active primarily against gram-positive bacteria and disrupts membranes?

Daptomycin.

Give two reasons biofilm bacteria are harder to treat than planktonic cells.

Biofilm cells express different phenotypes and can be 1000× less sensitive to antibiotics; extracellular matrix hinders drug penetration.

Why is antifungal therapy more difficult than antibacterial therapy?

Fungal cells are eukaryotic and share many cellular features with human cells, increasing host toxicity risk.

What is the primary mode of action of amphotericin B?

It binds to fungal cell membranes causing loss of selective permeability.

Which azole antifungal is commonly used for AIDS-related cryptococcal meningitis?

Fluconazole.

Name one echinocandin and its target.

Caspofungin; inhibits fungal cell-wall synthesis (β-glucan synthesis).

What is the classic antimalarial drug historically derived from cinchona bark?

Quinine (now largely replaced by chloroquine, primaquine, ACTs).

Which drug is the mainstay for anaerobic protozoan infections such as amebiasis?

Metronidazole.

List two common antihelminthic drugs.

Albendazole and praziquantel (others: pyrantel, ivermectin).

State the three major modes of action of antiviral drugs.

Prevent viral entry, block nucleic acid synthesis, and inhibit viral assembly/release.

What entry inhibitor prevents fusion of HIV with host cells?

Enfuvirtide (Fuzeon).

Which neuraminidase inhibitors block influenza A & B entry and release?

Oseltamivir (Tamiflu) and zanamivir (Relenza).

Name the nucleotide analog that terminates RNA replication in SARS-CoV-2.

Remdesivir.

What class of drugs, such as indinavir, blocks HIV protease?

Protease inhibitors.

Differentiate intrinsic and acquired drug resistance.

Intrinsic resistance is natural to the organism; acquired resistance arises through mutation or horizontal gene transfer of resistance genes.

What are R-factors and how are they transferred?

Resistance plasmids carrying drug-resistance genes; transferred via conjugation, transformation, or transduction.

List five cellular mechanisms microbes use to resist antimicrobials.

1) Enzymatic drug inactivation, 2) Decreased drug permeability, 3) Active efflux pumps, 4) Altered drug targets, 5) Bypassing inhibited metabolic pathways.

Explain how natural selection promotes antibiotic resistance.

Drugs kill susceptible bacteria, leaving naturally resistant ones to survive and reproduce, eventually dominating the population.

Why is overprescription for viral respiratory infections problematic?

It exposes microbes unnecessarily to antibiotics, selecting for resistant strains without clinical benefit.

What percentage of U.S. antibiotics is estimated to be used in livestock?

Nearly 80%.

Define ‘superinfection’ and give one example.

Disease that results when normal microbiota are disrupted allowing opportunists to overgrow; e.g., Clostridioides difficile colitis after broad-spectrum antibiotics.

Which organ systems are most frequently affected by antimicrobial toxicity?

Liver (hepatotoxic), kidneys (nephrotoxic), GI tract, blood/cardiovascular (hemotoxic), nervous system (neurotoxic).

Which antibiotic class causes kidney damage and weakened muscular responses?

Polymyxins.

What CDC category designates the most critical antibiotic-resistant threats?

Urgent threats (e.g., carbapenem-resistant Acinetobacter, C. difficile, C. auris, CRE).

Give two novel antimicrobial strategies under investigation.

Nanomaterials, CRISPR gene-editing, antisense RNA, bacteriophage therapy, or drugs targeting gram-negative outer-membrane proteins.

Define probiotics and state their purpose.

Live microorganisms administered to improve or restore normal intestinal biota.

What are prebiotics?

Nutrients (e.g., fructans) that stimulate the growth of beneficial gut microbes.

What therapy involves transplanting normal fecal microbiota to a patient?

Fecal microbiota transplantation (FMT), often for recurrent C. difficile infection.

Which test provides both MIC values and a visual zone of inhibition on an agar plate?

Etest strip diffusion assay.

What is the ‘therapeutic window’?

The drug blood-level range that achieves therapeutic effect without toxicity.

Which sulfonamide is commonly used topically for burn treatment?

Silver sulfadiazine.

Why are cell-wall–targeting drugs generally more selectively toxic than membrane-targeting drugs?

Human cells lack peptidoglycan walls, whereas membranes are more similar between microbes and humans, raising toxicity risk.

Which older aminoglycoside was the first to be used clinically and is still employed for tuberculosis?

Streptomycin.

Name the β-lactam antibiotic reserved for those allergic to penicillin and targeting gram-negative aerobes.

Aztreonam (a monobactam).

What is the principal effect of antibiotics on the human microbiome over time?

Loss of microbial diversity and enrichment of resistance genes, increasing risks for disorders such as C. difficile infection, obesity, and diabetes.