JEFFERSON COMMUNITY & TECHNICAL COLLEGE Jefferson Community and Technical College MLT 207: Introduction to Clinical Diagnostic Microbiology Module 10: Antimicrobial Susceptibility Testing Study Sheet 1. List characteristics of antibiotics: 2. Define the following terms related to antibiotics and bacterial resistance: a. Broad-spectrum: b. Narrow spectrum: c. Bactericidal: Exert lethal effects on microorganism d. Bacteriostatic: Inhibit bacterial growth but do not kill the organism e. Intrinsic Resistance: f. Acquired Resistance: g. Biofilm: A group of bacteria live as part of a matrix of bacteria that irreversible attach to a surface h. Impermeability: i. Efflux: 3. List the most common resistance mechanisms used by bacteria against antibiotics:
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- They can be classified based on their mechanism of action, spectrum of activity, and chemical structure. - Antibiotics can be bactericidal (kill bacteria) or bacteriostatic (inhibit bacterial growth). - They can target specific components of bacterial cells, Show more…
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Antibiotic resistance, microbial antagonism, and therapeutic use - Chapter 12 Continued NDM-1 carrying bacteria are resistant to antibiotics that inhibit PG synthesis enzymes. MRSA stands for Methicillin Resistant Staphylococcus Aureus, resistant to Beta-lactam antibiotics. KPC stands for Klebsiella pneumoniae Carbapenemase, an enzyme that inactivates the antibiotic carbapenem and all other Beta-lactam antibiotics. Instructions: Make a concept map or table (handwritten) of the mechanisms of resistance of the above types of resistant bacteria. Indicate or provide a short explanation of how each mechanism of resistance is acquired. Answer this question (handwritten): How do populations of bacteria evolve to become resistant over time? Why does this process happen relatively quickly?
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Study Questions: 1. Which antibiotic seems to be most effective in inhibiting E. aerogenes? Which antibiotic seems to be least effective? Justify your choices. 2. Which organism was penicillin most effective against? Least effective against? How can you explain this difference? 3. If the zones of inhibition of two antibiotic disks (A and B) on a Sarcina lutea dish measure 17 and 18 mm respectively, which antibiotic is more effective against Sarcina lutea. Why? 4. Do the antibiotics kill the bacteria or only inhibit the growth? Design a method to determine whether the antibiotics are bacteriostatic (inhibit) or bactericidal (kill). 5. If the antibiotic concentration is doubled, will the growth zone be twice as large? Explain. 6. A doctor is prescribing medicine for a person with a systemic E. coli infection (a systemic infection is disseminated throughout the body by the circulatory system). Which antibiotic might a doctor choose? Hint: E. coli belongs to the same class of bacteria as Enterobacter aerogenes. Organism | Chloramph. | Penicillin | Tetra. E. aerogenes | 30 | 8 | 24 B. cereus | 5 | 5 | 5 S. lutea | 5 | 5 | 5 Chart 1: Zones of Inhibition (diameter in mm) Dish Diagram
Antibiotic resistance is becoming common among organisms that cause a variety of human diseases. All of the following strategies help reduce the risk of antibiotic resistance evolving in a susceptible bacterial population except A. using antibiotics only when appropriate, for bacterial infections that are not clearing up naturally; B. using the drugs as directed, taking all the antibiotic over the course of days prescribed; C. using more than one antibiotic at a time for difficult-to-treat organisms; D. preventing natural selection by reducing the amount of evolution the organisms can perform; E. reducing the use of antibiotics in non-health-care settings, such as agriculture.
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