Part 2: Antimicrobial Drugs

What are different types of antimicrobials

• antibiotics

• antifungals

• antivirals

• antiprotozoals

What are important qualities of antimicrobial drugs?

• selective toxicity

• mode of action

Selective toxicity of antimicrobials

• selectively kills/ inhibits growth of microbial targets while causing minimal or no harm to host

Mode of Action in antimicrobials

• how drugs effect microbes at the cellular level

Penicillin

• natural antibiotic

• first to be discovered

Methicillin

• more resistant to penicillinases that were inactivating other penicillins

• semi-synthetic

Methicillin-resisatant Staphylococcus aureus

• being countered using a 5th generation drug from the family cephalosporins

What feature of antibiotics can disrupt the cell wall?

• Beta-lactam ring

How does beta-lactan disrupt the cell wall?

• penicillin binding proteins

• peptidoglycan subunits

• peptidoglycan subunit transport

what drugs disrupt the bacterial cell wall

B-lactams

• penicillins

• cephalosporins

• monobactams

• carbapenems

What binds to 30S ribosomal subunits and impairs proofreading?

• Aminoglycosides

What binds to 30S ribosomal subunits and blocks binding to tRNAs?

• Tetracyclines

What antimicrobials block protein biosynthesis by targeting 30S ribosomes?

• Aminoglycosides

• Tetracyclines

What drugs bind to 50S ribosomal subunits, prevent peptide bond formation and stop protein synthesis?

• Chloramphenicol

• Macrolides

• Lincosamides

What does rifampin do?

• inhibit bacterial RNA polymerase activity

• blocks transcription

• kills cell

What antimicrobials inhibit nucleic acid synthesis?

• rifamycin

• fluoroquinolones

What does fluoroquinolone do?

• inhibits DNA gyrase active

• blocks DNA replication

• kills the cell

What antimicrobials inhibit metabolic pathways?

• sulfonamides

• trimethoprim

Sulfonamides

• block bacterial biosynthesis of folic acid, pyrimidines, and purines

Trimethoprim

• structural analogue of dihydrofolic acid that inhibits steps later in metabolic pathway

What causes drug resistance to occur?

• overuse/misuse of antimicrobials

• inappropriate use

• therapy dozing

• patient non compliance with recommended course of treatment

What are the two ways bacteria acquire drug resistance

• chromosomal mutations

  • vertical transmission

• drug resistance genes on plasmids or transposons

  • horizontal transmission

Why does it increase the likelihood of developing antibiotic resistance if antibiotic treatment is stopped before the full prescribed course of treatment? 

• allows the strongest, most resilient bacteria, which survive the initial doses

• becoming superbugs that future treatments can't kill

What are different mechanisms of drug resistance?

• target modification

• Efflux Pump

• reduced cell penetration

• inactivation of enzymes

Multidrug-resistant microbes

• superbugs

• carry >1 resistance mechanism

• makes them resistant to multiple antimicrobials

Cross-resistance

• single resistance mechanism confers resistance of multiple antimicrobial drugs

What is an example of cross-resistance?

• efflux pump that can export multiple antimicrobial drugs