MASTERING MICROBIOLOGY: Chapter 20 Tutorial

Part H - How Do Microorganisms Acquire Antibiotic Resistance? Identify the statements below that accurately describe the mechanisms through which organisms acquire antibiotic resistance. Select all of the statements that accurately describe the origins and spread of antibiotic resistance.

*Antibiotics select for those microbes that have developed resistance, increasing their frequency in the bacterial population. *Antibiotic-resistance genes can be passed from one bacterium to another by bacterial transformation. *Antibiotic resistance is readily transmitted to the next generation during binary fission. *Mutations are the ultimate source of antibiotic-resistance genes. *Antibiotic-resistance genes can be passed horizontally via transduction. *Antibiotic-resistance genes can be passed horizontally via bacterial conjugation.

One approach that is becoming more common in drug D&D is to search for antimicrobial-producing organisms in relatively pristine environments. A pristine environment is one that has been relatively unperturbed by humans and/or domestic animals. Your D&D team is searching for novel antimicrobials produced by bacteria in a remote area of a temperate rainforest in the Pacific Northwest. Which of the following terms would accurately describe your drug? Select all that apply.

*natural *antibiotic *chemotherapeutic agent

Part E While in the development phase, you are also required to determine both the minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) for your drug. While these values directly relate to the efficacy of the drug against bacteria, they will also be informative for the next stages of development, which include studies to determine effective dosages within a host. The picture depicts the results of an MBC test. Based on these data, the MIC for your drug would be __________ and the MBC would be __________.

8 μg/ml; 16 μg/ml

A Gram-positive bacterial strain is simultaneously treated with two different antimicrobials: Drug A, which targets a protein involved in cell wall synthesis, and Drug B, which targets ribosomes involved in translation. The bacteria continue to grow during the course of treatment, indicating resistance to both antimicrobials. What are all the possible resistance mechanisms this bacterial strain could have? Check all that apply.

ALL ANSWER CHOICES

You are working in a research lab with a doxycycline-resistant strain of Klebsiella pneumoniae isolated from a patient. To investigate this strain's drug resistance mechanism, you set up a bacterial growth study using the resistant strain and a non-resistant control strain of K. pneumoniae. You inoculate several broth tubes with the same density of bacteria, using either the resistant or control strain. Each tube is then incubated in the presence of a particular concentration of doxycycline (none/control, low, or high). In addition, you perform similar exposures to other tubes in the presence of the efflux pump inhibitor phenylalanine arginine β-naphthylamide (PAβN). The graphs below show the final bacterial densities in the tubes after 24 hours of treatment. Assume the concentration of PAβN used is sufficient to completely block efflux pumps, if they're present. Based on the data shown, what are the possible resistance mechanisms of this patient's resistant strain of K. pneumoniae?

ALL ANSWER CHOICES

Antimicrobial X targets a specific protein in the cytoplasm of the bacterial cell, causing the bacteria to stop growing, but does not kill them. A few bacteria start to grow in the presence of antibiotic X. Analysis of the bacteria that can now grow shows that they have changed the shape of the target for antimicrobial X. What conclusion can be made?

Antimicrobial X is less effective against the new shape of its target.

Part A Each phrase below is applicable to a particular mechanism of antimicrobial resistance. Match each phrase to its respective mechanism. Each phrase below is applicable to a particular mechanism of antimicrobial resistance. Match each phrase to its respective mechanism.

DRUG INACTIVATION: *Bacterial β -lactamases *Antimicrobial altered EFFLUX PUMPS: *Active transport *Antimicrobial moved from inside to outside of cell *Turning on transport mechanisms DECREASED PERMEABILITY: *Bacterial porins *Turning off transport mechanisms ALTERED BINDING SITE: *Structural changes of drug target *Mutation of drug target

Penicillin's target is transpeptidase, a protein involved in cell wall synthesis. For a Gram-positive bacterium, which of the following mechanisms would be most effective in resisting penicillin's effects?

Drug inactivation via β-lactamases and altered target binding site

Part G - Examples of Antibiotic Resistance Part complete There are numerous examples of microorganisms displaying each of the four major resistance mechanisms. In this activity, you are asked to identify the mechanism that each example best illustrates. Drag each item into the appropriate bin.

ENZYMATIC INACTIVATION OF THE ANTIBIOTIC: Many strains of Neisseria gonorrhoeae are resistant to penicillin because of the production of β -lactamases.Many strains of Neisseria gonorrhoeae are resistant to penicillin because of the production of β-lactamases. PREVENTION OF PENETRATION TO THE TARGET SITE WITHIN THE MICROBE: Resistance to tetracycline may result from modified pore proteins in the outer membrane that form a porin too small for the tetracycline to pass through. ALTERATION OF THE DRUG'S TARGET SITE: *Resistance to clindamycin develops when mutations in bacteria alter the ribosomal binding site to which clindamycin would normally bind. MRSA (methicillin-resistant Staphylococcus aureus) is resistant to all β -lactam drugs because of a mutation in its penicillin-binding protein (PBP). *MRSA (methicillin-resistant Staphylococcus aureus) is resistant to all β-lactam drugs because of a mutation in its penicillin-binding protein (PBP). RAPID EFFLUX OF THE ANTIBIOTIC: Pseudomonas aeruginosa has membrane pumps that export a number of different antibiotics from its cells.

Why are chemotherapeutic agents that work on the peptidoglycan cell wall of bacteria a good choice of drug?

Humans and other animal hosts lack peptidoglycan cell walls.

Part B - How Do Antimicrobial Drugs Inhibit Bacterial Growth? In this activity, you will identify the general mechanism of inhibition for the antimicrobial actions listed. Drag each item into the appropriate bin.

INHIBITING CELL WALL SYNTHESIS: *Inhibiting synthesis of peptide cross-links *Inhibiting bonding of N-acetyl glucosamine to N-acetylmuramic acid *Inhibiting lipopolysaccharide synthesis *Inhibiting mycolic acid synthesis INJURING THE PLASMA MEMBRANE: * Inhibiting fatty acid synthesis INTERFERING WITH DNA REPLICATION: *Interfering with DNA polymerase *Inhibiting DNA gyrase INTERFERING WITH PROTEIN SYNTHESIS: Interfering with activity of 30S ribosomal subunit *Interfering with activity of 50S ribosomal subunit *Interfering with attachment of tRNA to mRNA *Interfering with peptide bond formation, catalyzed by the ribosome

PART D In order to gain FDA approval for your drug, you must elucidate its mechanism of action (MOA). MOA refers to the particular pathway/ process/molecule that will directly be impacted by your drug. Current antibiotic therapies against bacterial infection use one of five characterized mechanisms. Match each antibiotic (and its functional description) with the appropriate mechanism of action.

INHIBITION OF CELL WALL SYNTHESIS: Penicillin (Right Side) INHIBITION OF : Streptomycin DISRUPTION OF CYTOPLASMIC MEMBRANE: Gramicidin (bottom) INHIBITION OF GENERAL : Sulfanilomide INHIBITION OF DNA OR RNA SYNTHESIS: Trifluridine

Which mode of action of antimicrobial drugs involves competitive inhibition between sulfanilamide and para-aminobenzoic acid (PABA)?

Inhibition of essential metabolite synthesis

Why is polymyxin only used on the skin?

It can also damage living human cell membranes, but the drug is safely used on the skin, where the outer layers of cells are dead.

One aspect that must be evaluated during the development phase is the interaction of your drug with the host (i.e., what effect will the drug have on human cells?). There are several important factors to consider in this interaction, including the selective toxicity of your potential drug. Which of the following statements most accurately describes the principle of selective toxicity?

Selective toxicity refers to the ability of an antimicrobial to kill microbes with minimal damage to the host.

Part C - The Penicillins Part complete All penicillins, or "cillins," share several structural features but differ in others. This activity asks that you identify several features common to all "cillin" antibiotics. Drag the labels to the appropriate locations on the image.

TOP: Common nucleus LEFT SIDE: Side chain BOTTOM: B-Lactam ring

Part F - Mechanisms of Antibiotic Resistance, Part 2Part complete There are basically four mechanisms of microbial resistance. This activity asks that you drag the statement describing each mechanism to the appropriate area of the image that represents the mechanism. Drag each statement to the appropriate area of the diagram.

TOP: Entry of antibiotic into the cell is blocked. RIGHT SIDE: Cellular enzyme inactivates an antibiotic. LEFT SIDE: Target site to which antibiotic binds is altered. BOTTOM: Efflux mechanism pumps antibiotic out of the cell.

Part A The project that you are working on was initiated in response to the growing threat of antibiotic resistance in both hospital and community settings. Even in the early discovery and development phase, it is important to think ahead to try to minimize the likelihood that bacteria will be able to evolve resistance to your new drug. Understanding how resistance emerges is an essential part of this process. Which of the following statements is NOT true regarding the evolution of antibiotic resistance in bacteria?

The exposure of bacteria to an antibiotic causes the bacteria to produce resistance genes.

There are a large number of antibiotics that inhibit protein synthesis at 70S ribosomes found in bacterial cells but do not interfere with protein synthesis at the 80S ribosomes found in eukaryotic cells. Some of these antibiotics bind to the smaller ribosomal subunit and interfere with the reading of the mRNA code, whereas others bind to the larger ribosomal subunit and inhibit the formation of peptide bonds. Unfortunately, some of the antibiotics that inhibit protein synthesis in bacteria exhibit some toxicity to the eukaryotic host cells as well. What is the most likely reason for this toxicity to the host cell?

These antibiotics interfere with protein synthesis within eukaryotic mitochondria.

Why is it difficult to find good chemotherapeutic agents against viruses?

Viruses depend on the host cell's machinery, so it is hard to find a viral target that would leave the host cell unaffected.

Part E - Mechanisms of Antibiotic Resistance, Part 1Part complete Consider the different mechanisms through which antibiotics inhibit microbial growth, and consider what changes in the microbe might enable it to resist the inhibitory effects of antibiotics. Select all of the statements that describe a mechanism that would enable a microorganism to resist the action of an antibiotic.

*An enzyme that destroys the antibiotic is produced. *Target site is modified, so that an antibiotic is unable to bind to its target. *Altered porins in the cell wall block passage of antibiotic through the cell wall. *A microbe develops a transport mechanism in the plasma membrane that rapidly pumps antibiotic out of the bacterial cell.

What is meant by selective toxicity?

Chemotherapeutic agents should act against the pathogen and not the host.

Quinolones and fluoroquinolones act against what bacterial target?

DNA gyrase

Why is chloramphenicol effective against prokaryotes but not eukaryotes?

Due to the 70S prokaryotic structure, chloramphenicol inhibits protein synthesis selectively in prokaryotes.

Which of the following drugs does NOT act by inhibiting protein synthesis?

Sulfanilamide

If a patient were infected with chlamydias microorganisms, which drug would be the treatment of choice?

Tetracycline