Microbiology Chapter 20 Flashcards

Questions and Answers

What is meant by selective toxicity?

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

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.

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.

Quinolones and fluoroquinolones act against what bacterial target?

DNA gyrase. Signup and view all the answers

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. Signup and view all the answers

If penicillin G is chosen as the best treatment for a given infection, what microorganisms are most likely the cause?

gram-positive bacteria. Signup and view all the answers

Why is methicillin-resistant Staphylococcus aureus (MRSA) methicillin resistant?

It produces a modified version of the molecule that is targeted by the drug. Signup and view all the answers

Why is it more difficult to treat viral infections than it is to treat bacterial infections?

Viruses use the host cell's processes to carry out their own reproduction. Signup and view all the answers

A new bacterial molecule is discovered that inactivates an antibiotic. Which category best describes the mechanism of antibiotic resistance conferred by this molecule?

bacterial enzymes. Signup and view all the answers

Which antibiotic is overcome by beta-lactamases?

Penicillin. Signup and view all the answers

How might efflux pumps increase antibiotic resistance in bacteria?

Resistant bacteria can have more efflux pumps, and can have less specific efflux pumps. Signup and view all the answers

Bacteria that are resistant to sulfonamide have enzymes that have a greater affinity for what?

PABA. Signup and view all the answers

Why would an efflux pump for penicillin located on a bacterial cell membrane not be effective at providing resistance to the drug?

Penicillin disrupts the cell wall, which is located outside of the cell membrane. Signup and view all the answers

Membrane transport proteins are required for which mode(s) of antibiotic resistance?

Efflux pumps, beta-lactamases, and modification of porins all utilize membrane transport proteins. Signup and view all the answers

What is meant when a bacterium is said to become 'resistant' to an antibiotic?

The bacterium is neither killed nor inhibited by the antibiotic. Signup and view all the answers

When a patient is treated with antibiotics, __________.

the drug will kill or inhibit the growth of all of the sensitive bacterial cells. Signup and view all the answers

The process of acquiring antibiotic resistance by means of bacteriophage activity is called?

transduction. Signup and view all the answers

Which of the following mutations would not result in antibiotic resistance?

Silent mutation. Signup and view all the answers

R-plasmids are most likely acquired via?

bacterial conjugation. Signup and view all the answers

Consider a Kirby-Bauer disk-diffusion assay. If you put penicillin and streptomycin disks adjacent to one another, the zone of inhibition is greater than that obtained by either disk alone. This is an example of __________.

synergism. Signup and view all the answers

Which of the following would be selective against the tubercle bacillus?

ethambutol - inhibits mycolic acid synthesis. Signup and view all the answers

Drug resistance occurs?

when antibiotics are used indiscriminately. Signup and view all the answers

Which of the following statements about drug resistance is FALSE?

It is found only in gram-negative bacteria. Signup and view all the answers

Which of the following organisms would MOST likely be sensitive to natural penicillin?

Streptococcus pyogenes. Signup and view all the answers

The antimicrobial drugs with the broadest spectrum of activity are?

tetracyclines. Signup and view all the answers

To date, most of our natural antibiotics have been found to be produced by members of what genus?

Streptomyces. Signup and view all the answers

More than half of our antibiotics are?

produced by bacteria. Signup and view all the answers

Which of the following antibiotics is recommended for use against gram-negative bacteria?

polymyxin. Signup and view all the answers

Which of the following antimicrobial agents has the fewest side effects?

penicillin. Signup and view all the answers

In what way are semisynthetic penicillins and natural penicillins alike?

Both are based on β-lactam. Signup and view all the answers

Penicillin was considered a 'miracle drug' for all of the following reasons EXCEPT?

it was the first antibiotic. Signup and view all the answers

Which statement regarding tests for microbial susceptibility to chemotherapeutic agents is FALSE?

The Kirby-Bauer test is useful because it can differentiate bacteriostatic effects from bactericidal effects. Signup and view all the answers

Study Notes

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.

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Description

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.