Glycopeptide Antibiotics and Other Cell Wall Or Membrane-Active Agents

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Questions and Answers

What does MIC stand for in microbiology?

Microbial Inhibition Control

Maximum Inhibitory Concentration

Minimum Inhibitory Capacity

Minimum Inhibitory Concentration (correct)

How is MBC different from MIC?

MBC tests the effect of increasing concentrations of antibiotic, while MIC tests decreasing concentrations.

MBC indicates the highest concentration of the antibacterial agent, while MIC indicates the lowest.

MBC shows the level of agent that inhibits growth, while MIC shows the one that kills bacteria.

MBC is the lowest level of antimicrobial agent resulting in microbial death, MIC is the lowest level of antimicrobial agent that greatly inhibits growth. (correct)

Why might a bacterium survive even if the MIC test shows inhibition?

The bacterium was already dead before the test.

Because the bacterium has an inherent resistance to antimicrobials.

Due to the absence of antimicrobial agents in the environment.

The bacterium was only momentarily inhibited by the agent. (correct)

When are antibacterial agents considered bactericidal according to the text?

If their MBC is less than four times their MIC. Signup and view all the answers

Which statement best explains the purpose of measuring MBC in microbiology?

To ensure complete eradication of bacteria with the lowest effective dose. Signup and view all the answers

Which antibiotic group also acts on the cell membrane like Vancomycin?

Glycopeptide Proteins Signup and view all the answers

Leading cause of nosocomial (hospital related) infections and are known to be resistant to antimicrobial products, except

Streptococcus pneumoniae Signup and view all the answers

What contributes to resistance to Vancomycin in bacteria?

Modification of the peptidoglycan binding site Signup and view all the answers

What is the primary action of Vancomycin in inhibiting bacterial growth?

Disrupting cell wall synthesis Signup and view all the answers

Which type of bacteria is primarily targeted by Vancomycin?

Gram-positive bacteria Signup and view all the answers

What is the usual bactericidal concentration range of Vancomycin?

0.5–10 mcg/mL Signup and view all the answers

Which bacterium is associated with the production of Cycloserine?

Streptomyces orchidaceous Signup and view all the answers

What is a major side effect associated with Cycloserine use?

Headaches, tremors, and acute psychosis Signup and view all the answers

Which bacterial infections is Cycloserine commonly used to treat?

Tuberculosis Signup and view all the answers

Why should Cycloserine not be applied to wounds for the purpose of preventing infection?

It is ineffective at preventing infection Signup and view all the answers

Which enzyme does Cycloserine inhibit in bacterial cells?

Alanine racemase Signup and view all the answers

Which type of bacteria does Cycloserine inhibit?

Both Gram-positive and Gram-negative Signup and view all the answers

How is Cycloserine excreted from the body?

In active form into the urine Signup and view all the answers

Which type of infection is commonly treated with parenteral Vancomycin in combination with Cefotaxime, Ceftriaxone, or Rifampin?

Meningitis Signup and view all the answers

How is Vancomycin primarily administered due to its poor absorption from the intestinal tract?

Intravenously Signup and view all the answers

Important indications for parenteral Vancomycin are bloodstream infections and endocarditis caused by:

MRSA Signup and view all the answers

Why is Bacitracin not used systemically and is only applied topically?

Highly nephrotoxic when administered systemically Signup and view all the answers

What is the mechanism of action of Bacitracin against microorganisms?

Inhibits cell wall formation Signup and view all the answers

Why is Bacitracin only used topically and not systemically?

Poor absorption from the intestinal tract Signup and view all the answers

What is the primary concern when using Bacitracin systemically?

Nephrotoxicity Signup and view all the answers

Study Notes

MIC and MBC

MIC stands for Minimum Inhibitory Concentration, the lowest concentration of an antibacterial agent that inhibits bacterial growth.
MBC (Minimum Bactericidal Concentration) is different from MIC in that it is the lowest concentration of an antibacterial agent that kills 99.9% of bacteria.
A bacterium may survive even if the MIC test shows inhibition if the bacterium is not killed by the antibacterial agent, but only inhibited.

Antibacterial Agents

Antibacterial agents are considered bactericidal if they can kill 99.9% of bacteria at a specific concentration.
Measuring MBC is important to determine the concentration of an antibacterial agent needed to kill bacteria, rather than just inhibit growth.
Vancomycin is a bactericidal antibiotic that acts on the cell membrane, similar to Polymyxins.

Vancomycin

Vancomycin is primarily used to target Gram-positive bacteria, particularly Staphylococcus aureus and Streptococcus pneumoniae.
The primary action of Vancomycin is to inhibit bacterial cell wall synthesis by binding to the D-Ala-D-Ala terminus of peptidoglycan.
The usual bactericidal concentration range of Vancomycin is 1-4 μg/mL.
Resistance to Vancomycin in bacteria can occur due to the alteration of the D-Ala-D-Ala terminus of peptidoglycan.

Cycloserine

Cycloserine is an antibiotic produced by Streptomyces orchidaceus.
A major side effect of Cycloserine use is neurological toxicity, including seizures and psychosis.
Cycloserine is commonly used to treat tuberculosis and other infections caused by Mycobacterium tuberculosis.
Cycloserine should not be applied to wounds to prevent infection because it can cause neurological toxicity and is not effective against most bacteria.
Cycloserine inhibits the enzyme D-alanine:D-alanine ligase in bacterial cells, which is necessary for peptidoglycan synthesis.
Cycloserine is primarily excreted from the body through the kidneys.

Clinical Applications

Vancomycin is often administered in combination with Cefotaxime, Ceftriaxone, or Rifampin to treat meningitis and other infections.
Vancomycin is primarily administered intravenously due to its poor absorption from the intestinal tract.
Parenteral Vancomycin is indicated for bloodstream infections and endocarditis caused by methicillin-resistant Staphylococcus aureus (MRSA) and other Gram-positive bacteria.

Bacitracin

Bacitracin is not used systemically due to its nephrotoxicity and is only applied topically.
The mechanism of action of Bacitracin is to inhibit the dephosphorylation of C55-polyisoprenyl diphosphate, which is necessary for peptidoglycan synthesis.
Bacitracin is only used topically because of its nephrotoxicity, which can cause kidney damage when used systemically.

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Test your knowledge on Minimum Inhibitory Concentration (MIC) which is the lowest concentration of an antimicrobial agent that prevents the visible growth of bacteria. Evaluate the antimicrobial efficacy of various compounds by measuring the effect of decreasing concentrations of antibiotics/antiseptics over a defined period in terms of inhibition of microbial population growth.