Chapter 14: Antimicrobial Drugs

Characteristics of the ideal antimicrobial drug

1) selective toxicity

2) microbicidal, not microbistatic

3) Soluble

4) Remains potent long enough to act

5) Doesn't lead to antimicrobial resistance

Charateristics of the ideal antimicrobial drug

6) Complement's hosts defenses

7) Remains active in tissues/body fluids

8) Easily delivered to site of infection

9) Doesn't cause other health problems like allergies or predisposed to other infections

Antibacterial drugs

▪ Antibiotics (Natural)

▪ Semisynthetic drugs

▪ Synthetic drugs

Antibiotics

Naturally occurring antimicrobials.

Metabolic products of bacteria and fungi

Reduce competition for nutrients and space

What does bacteria produce?

Streptomyces and Bacillus

What does mold produce ?

Penicillium and Cephalosporium

Modes of antimicrobial action

-inhibition of cell wall synthesis

-inhibition of protein synthesis

-inhibition of nucleic acid replication and transcription

-injury to plasma membrane

-inhibition of synthesis of essential metabolites

Microbial Death

stopping reproduction

The best mode of antimicrobial action is?

Inhibition of cell wall synthesis (directly kills bc its opening the cell)

Who is Alexander Fleming?

The guy who discovered the first natural antibiotic

Narrow-spectrum

affects only a select group of microbes

Narrow-spectrum advantage?

your body will still have all the beneficial bacteria since you narrowed down and targeted a certain bacteria

Narrow-spectrum Disadvantage?

You will have to wait until the organism is identified; it will take time. Can’t be used in urgent situations.

Broad-spectrum

affects a more diverse range of microbes

Broad-spectrum advantage?

All the bad bacteria will be gone

Broad-spectrum disadvantage?

Will kill all bacteria, even the good

Fungal, protozoan, and helminthic infections are more difficult to treat because?

Because they are eukaryotic, they have more similarities to human cells, making it even harder to target.

β-lactams block what?

the synthesis of peptidoglycan, causing the cell wall to lyse

β-lactams ALL contain?

A highly reactive 3-C, 1-N ring

What are examples of β-lactams?

Penicillin and Cephalosporin

Are beta-lactams easy to target?

YES

β-lactams are less effective against Gram-negative bacteria because?

• because gram-negative bacteria has an outer membrane and inner membrane that does not allow it to pass through

• Gram-negative bacteria have a thinner peptidoglycan layer compared to Gram-positive bacteria.

What are Semisynthetic penicillin

ampicillin, carbenicillin, and amoxicillin

Semisynthetic penicillin (ampicillin, carbenicillin, and amoxicillin)

have broader spectra. What does this mean?

Semisynthetic penicillins — like ampicillin, carbenicillin, and amoxicillin — can kill or fight a wider range of bacteria compared to regular (natural) penicillin. In other words, they work against more types of bacteria.

Penicillin binding proteins

make peptide bonds to cross link proteins

Penicillinase

enzyme that can break the link of penicillin drugs

Selective toxicity is almost impossible in viruses because?

Viruses are intracellular parasites that live and reproduce inside the host’s cells. Since they use the host’s own cell machinery to make more viruses, it’s hard to find a drug that can kill the virus without also harming the host’s cells.

Antiviral drugs do what?

• Block penetration into the host cell

• Block replication, transcription, or translation of viral genetic material

Protease inhibitors

HIV

Selective toxicity

The drug kills pathogens without damaging the host

Drug Resistance

Adaptive response to drugs
-due to genetic versatility or variation
-intrinsic and acquired (intrinsic: vertical gene transfer)

What are the two main mechanisms of acquired resistance?

• Spontaneous mutations in critical chromosomal genes

• Acquisition of new genes from another species (horizontal gene transfer)

How do organisms become resistant to drugs?

• Efflux Pump

• Blocked penetration

• Inactivation of enzymes

• Target modification

Misuse of antibiotics leads too?

Antibiotic resistance

How can acquired resistance occur through mutations?

Spontaneous mutations in critical chromosomal genes

How can acquired resistance occur through gene transfer?

Acquisition of new genes from another species

Misuse includes:

—Using outdated or weakened antibiotics

– Using antibiotics for the common cold and other

inappropriate conditions

– Using antibiotics in animal feed

– Failing complete the prescribed regimen

– Using someone else's leftover prescription

Superinfections

Infections occur after or on top of an earlier infection, especially following treatment with broad-spectrum antibiotics.

What percentage of people taking antimicrobials will experience a serious adverse reaction to the drug?

5 percent

What type of reaction might occur in some individuals when taking antimicrobials?

Serious adverse reaction - side effects

Major side effects:

1. Direct damage to tissue due to toxicity of drug
2. Allergic reactions
3. Disrupts the balance of normal flora

Disrupts the balance of normal flora is an example off?

A superinfection

Considerations in Selecting an Antimicrobial Drug

• Identify the microorganism causing the infection
• Test the microorganism's susceptibility (sensitivity)
• The overall medical condition of the patient

What type of test determines the smallest concentration of a drug needed to visibly inhibit microbial growth?

A dilution test to find the Minimum Inhibitory Concentration (MIC).

What general term describes the four major groups of antimicrobial drugs?

Antibacterial, antifungal, antiprotozoal, and antiviral drugs.

When is Testing the Effectiveness of Antimicrobials essential?

It is essential for groups of bacteria commonly showing resistance

Name the most common method used for drug susceptibility that involves antibiotic-impregnated disks.

The Kirby-Bauer disk diffusion test

Name another type of diffusion test used for drug susceptibility.

The E-test diffusion test

Define Minimum Inhibitory Concentration (MIC).

The smallest concentration of a drug that visibly inhibits growth