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Ch. 20 questions
Microbiology
| Question | Answer |
|---|---|
| Why were antibiotics called a miracle cure? | selective in that they could kill microbes without killing the patient |
| Compare the terms antibiotic and antimicrobic | antibiotic--means antilife--antimicrobial--more descriptive--denotes specificity of an agent for microbes |
| Differentiate between narrow-spectrum and broad-spectrum antibacterials | narrow-spectrum--target specific type of bacteria--broad-spectrum--inhibit growth of nearly all bacteria |
| What is the common problem of using a broad-spectrum antibiotic? | do not differentiate between undesirable microbes and normal flora--elininating normal fora--superinfection can result |
| Why do some bacteria and fungi produce antibiotics? | to inhibit other microbes and retain more nutrients |
| What is the importance of selective toxicity? | drug with completely selective toxicity--100% lethal to microbes--zero effect on patient--higher the selective toxicity--less likely patient will experience side effects |
| Which antibiotic is the most common to induce allergic reactions? Which one are not allergenic? | penicillin induces most allergic reactions--all antibacterials can be allergenic |
| What is a side effect of chloramphenicol treatment? | deppression of the immune system |
| Based on its mode of action, why is penicillin cidal? | because cell walls can't develop in its presence--become thinner and thinner until cytoplasmic membrane bulges out and cell lyses |
| Do drugs like penicillin and cephalosporin, which act on the cell wall, act equally well on growing and nongrowing bacteria? why/why not? | drugs do not work well on stationary-phase bacteria--cell walls are only weakened when cells try to make new PG that needs to be cross-linked into existing cell wall |
| Why do we call sulfa highly selective? | inhibit synthesis of folic acid--vitamin that bacteria and several other microbes must synthesize on their own--humans can't synthesize foclic acid--no inhibition to human cells |
| Name four other target sites for antibiotic action besides the cell wall | functions of 70S ribosomes in translational activity--inhibition of bacterial RNA synthesis--bacterial DNA synthesis--disruption of the cell membrane |
| How does B-lactamase protect a bacterium from penicillin or the third generation penicillin, cephalosporin? | B-lactamase--enzymes that degrades penicillins--changes in B-lactam make it resistant to original penicillinase--penicillinase mutated again--can degrade cephalosporins too |
| What is the noted mechanism of tetracycline resistance? | bacteria obtain a gene that pumps tetracycline from inside to outside of the cell |
| Are tetracyclines (one form of bacteriostatic drugs) narrow spectrum? Why/Why not? | tetracyclines are broad-spectrum antibiotics because all bacteria have 70S ribosomes |
| How can fungi become resistant to drugs that bind to ergosterol? | resistant fungi make less ergosterol--fewer targets for anti-ergosterol drugs to bind to |
| Drugs do not cause mutation, they select for resistant cells. Explain | if bacteria in the population are not killed or inhibited by drug--selected as the only ones that replicate and multiply |
| How can we minimize the spread of drug resistance? | reduce amounts of ABTs used in animal feeds, discourage indiscriminate use of ABTs in humans--give more than 1 ABT simultaneously to completely eleminate infections |
| Why do tetracyclines have limited use? | because bacteria have become resistant to them |
| What practices have led to widespread drug-resistant organisms? | unnecessary use of ABTs lead to widespread development of drug-resistant organisms |
| Why is it important to identify the pathogen before deciding on which therapy to use? | important to identify pathogen first so the ABT susceptibility of organism can be determined and correct ABT used |
| What is drug susceptibility testing and why is it done? | determines which drug will most effectively kill the isolated microbe |
| What does a larger zone of inhibition by infectious strain A relative to that of strain B indicate? | measures antibiotic potency and indicate which microbe is more susceptible to the drug |
| What is the Kirby-Bauer test? | bacteria spread on petri plate--antibacterial disks added on top--antibacterial chemicals diffuse into agar medium--kill/inhibit growth of susceptible organisms |
| What does MIC refer to? | minimum inhibitory concentration--used when microbes grown in liquid broth in tubes containing range of antimicrobial concentrations--lowest antimicrobial concentration inhibits microbial growth is MIC |
| How do the dilution tube and Kirby-Bauer tests work? | tube dilution--antibiotic serially diluted--determine what concentration drug will be effective--Kirby-Bauer --determins potency of antibiotic establishing zone of inhibition when antibiotic diffuses into agar plate |
| If a given drug has a therapeutic index of one hundred thousand, would that be considered good or bad? Explain | therapeutic index of 100,000--excellent--means the drug can be used clinically throughout a 100,000 fold range |
Created by:
heatherlvn
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