Chapter 20: Antimicrobial Drugs

Antiviral Drugs

- A virus enters a cell and uses the cells machinery to produce more virus particles. That means there are a limited number of targets. We target various stages of viral replication and also enzymes that are unique to the virus.

a. Staphylococcus aureus produces penicillinases making it resistant to many members of the penicillin family.

- Ampicillin is an extended spectrum antibiotic that is commonly used in biotechnology. It has increased activity against Gram - microbes.

Polypetide Antibiotics

- Bacitracin has a very low therapeutc index, making it very toxic to your cells. a. Bacitracin is very rarely given via injection but it is frequently used topically. i. Cell wall synthesis:

Cell Wall

- Cancidas inhibits the synthesis of β-glucan, an essential component of the fungal cell wall.

- There are several generations of cephalosporins. The first generation was effective against Gram + but improvements have made the subsequent generations into broad spectrum antibiotics.

- Cephalosporins can be resistant to beta-lactamase activity. Cephalosporinases do exist, and are capable of deactivating members of the cephalosporin family.

Cephalosporins

- Cephalosporins stop cell wall synthesis. How do the kill? osmotic lysis.

Protein Synthesis

- Characteristics of the Ribosome:

Terms

- Chemotherapy is the treatment of disease by a chemical compound that targets microbes or abnormal cells. - Antimicrobial are agents that kill or inhibit growth of susceptible organisms. Major Chemotherapeutic Agents:

History of Antimicrobials

- Ehrlich synthesized the drug salvarsan that was used to successfully treat syphilis. a. This STD is cause by Treponema pallidum, a bacterium that is spiral shaped.

Fungi

- General information/Stats: Fungal infections in hospitals are on the rise. They now make up ~9% of nosocomial infections. This is mainly because of the rise in the number of people with HIV.

Eukaryotic Pressure

- Malaria: caused by the protozoan Plasmodium falciparum. Transmission to humans via the bite of the female Anopheles gambiae. The eggs of Ascaris are commonly found in the dirt.

MRSA

- Methicillin-resistant Staphylococcus aureus a. Common in people with CF because of multiple antibiotic treatments b. Isolation. Highly contagious if in sputum.

Microtubules

- Mitosis is the cellular process that uses microtubules to segregate chromosomes prior to cell division. By inhibiting microtubule formation you stop mitosis.

Antibiotic Resistance

- Multiple antibiotics are frequently prescribed for a single patient. Of concern is how these drugs interact.

Synergism is when one antibiotic helps the other so you get a greater effect. If one antibiotic inhibits the activity of the other this is called antagonism.

- Nucleotide analogs have been developed that stop nucleic acid synthesis. AZT is an example of one of these drugs that is used to treat HIV+ individuals.

- Penicillin V is not destroyed by acid so it can be administered orally. It is active against Gram + and some Gram - organisms. It is not as active as penicillin G is against Gram - organisms.

- Oxacillin is a modified member of the penicillin family that is resistant to many penicillinase producing microbes.

Some can cross the placenta and can also be distributed to an infant via breast milk. When penicillin is able to reach its target, the cell will die via osmotic lysis.

- Penicillin G is given through the parenteral route because it is destroyed by acid. It can be distributed throughout the body with high levels in the kidneys. It is active against Gram + and some Gram - organisms.

Plasma Membrane

- Polymyxin B binds to the membrane making it more permeable. a. This is used mostly for resistant Gram negative organisms that are difficult to treat. It is toxic to neurons so its therapeutic index is low.

- Infections: a. septicemia, urinary tract infections, pneumonia, chronic lung infections, endocarditis.

- Resistance mechanisms a. Rapid Efflux pumps b. Low OM permeability c. R-factors

Nucleic Acid

- Rifamycin inhibits RNA synthesis and is commonly used to treat TB and Hansen's because both are caused by organisms of the Genus Mycobacterium. These organisms are slow growers so therapeutic treatments are given over several months.

- Quinolones and Fluoroquinolones are broad spectrum antibiotics that inhibit DNA gyrase. DNA gyrase activity is essential for DNA replication. a. Ciprofloxacin is used to treat anthrax and it is used to treat UTIs in an extended release version.

- Sulfonamides are agents that stop the synthesis of follic acid, a precursor for nucleotide synthesis. Competitve inhibitors bind to the active site of an enzyme and block the substrate from entering. a. Sulfanilamide is an example of a competitive inhibitor.

a. Antibiotics are antimicrobial agent produced by a microbe i. Bacteria and fungus are the most common producers of antibiotics.

- Synthetic drugs are products synthesized in lab that kills or inhibits the growth of a susceptible organism. a. Usually this is a modified antibiotic. They are usually modified to give it better or more powerful characteristics

Targets of Antibiotics

- The 3 major targets of antibiotics are the cell wall, the ribosome, and nucleic acid synthesis. - Other targets include enzymes and the cell membrane.

Antibacterial Antibodies

- The Penicillin Family: a. These are also called the beta lactams because of the β-lactam ring in all the members of this family. This β-lactam ring is essential for drug activity. (the beta lactam ring is blue in the figure to the left).

a. The major role of the cell wall is to prevent osmotic lysis. Several antibiotics stop cell wall synthesis. A compromised cell wall can lead to osmotic lysis, when conditions are appropriate (cell is hypertonic to the environment).

- The ribosome is the cellular machine that makes proteins and is the major target of several antibiotics. - Folic acid is necessary to make nucleotides. - Sulfanilamide was the competitive inhibitor that stopped the metabolic pathway from turning PABA into folic acid.

Mechanisms of Resistance

- Theinformation for these traits is usually encoded on a plasmid or transposon (jumping gene). These genetic elements can be easily transferred to bacteria of the same or different species.

Macrolipids (erythromycin)

- They have a broader spectrum than members of the penicillin family. It is often used when people are allergic to penicillin. These are commonly used to treat respiratory tract infections.

Mycobacterium Tuberculosis

- This microbe is resistant to many disinfectants because of its cell wall components. Its cell wall is made up of mycolic acid.

Pseudomonas Aeruginosa

- Tolerant to a variety of conditions - resistance to antibiotics and disinfectants - Slime layer =protection

VRE

- Vancomycin resistant Enterococcus a. Common infection in ICUs b. Enterococcus: GI tract. c. Symptoms/ sites of infection:

Tetracycline

- a broad spectrum antibiotic that stops tRNA molecules from bringing amino acids to the ribosome. a. It can be toxic to you because it can act on the ribosomes found in your mitochondria.

Neomycin

- an antibiotic found in Neosporin and it stops ribosome activity

Clostridium Difficile (C-Diff)

- anaerobic, spore forming rod - one of the most common hospital (nosocomial) infections - Role of broad spectrum antibiotic usage

Streptomycin

- causes the ribosome to incorrectly read the mRNA and is bactericidal. This results in mutant proteins. It was one of the first antibiotics used to treat tuberculosis. a. Gram - are more susceptible than Gram +. *Possible side effect: hearing loss.

Antibiotic Characteristics

- cide means that the drug kills - static means that the drug inhibits or stops growth.

Chloramphenicol

- inhibits the formation of the peptide bond between amino acids.

Stages of Viral Infection

1. Host cell recognition and binding. 2. Entry into the host cell 3. Taking over the host cell machinery 4. Producing new virions (virus particles) 5. Exit from the host cell

4 Common Mechanisms of Resistance

1. Modification or degradation of the antibiotic 2. Target molecule is charged 3. Decrease permeability or increase efflux 4. Enzyme bypass mechanisms.

Processes that don't Occur in Normal Cells

1. Reverse transcription a. In order to produce new virions nucleic acid replication is necessary. HIV has a RNA genome. This must be converted into DNA by the enzyme central dogma.

Criteria for Selecting Antibiotics

1. Selective toxicity: The antibiotics first given to a patient have a high therapeutic index. If those don't work, antibiotics with lower values are used.

This enzyme is unique to the virus because your cells do not normally possess this enzyme (selective toxicity).

2. HIV protease mediated post translational modification of proteins.

a. The product of HIV gene expression is a very long polypeptide. HIV protease cuts up this long polypeptide into multiple peptides.

Each peptide is then able to fold into its appropriate shape and the mature virus (capable of infecting more cells) can form. Without this enzyme the mature virus can not form.

Tolfnaftate is used to treat Tinea pedis, or athlete's foot. Dermatophytes are a group of fungi that cause skin disease.

How can you get athlete's foot? Dramatophytes

* When a bacterial cell makes it cell wall, components are first synthesized in the cytoplasm (region inside the membrane). These components are then exported across the plasma membrane and assembled. Bacitracin blocks the export of these cell wall components.

If the enzymes that synthesize the cell wall do not have the substrates to do so, then the cell wall will lose its integrity and the cell will die via osmotic lysis.

The major roles of it cell wall are: 1.resist dessication and chemicals 2. immune system evasion.

In order to stop this microbe you have to destroy its cell wall. Isoniazid inhibits mycolic acid synthesis and ethambutol inhibits mycolic acid incorporation into the cell wall.

ii. It is one of 3 antimicrobial agents in neosporin. iii. It is a narrow spectrum antibiotic that works well on Gram + organisms. - Vancomycin is called the "last line" of defense. Vancomycin is commonly used to treat Methicillin resistant Staphylococcus aureus (MRSA).

It has been overused so now there are resistant microbes appearing. MRSA is one of them that is a major concern because is some cases we do not have an antibiotic that will destroy this type of resistant microbe.

These round worms will inhabit the intestines absorbing nutrients and form a ball of worms called a bolus.

Most people do not know they have are infected with Ascaris until a worm comes out in their feces (anus).

a. The ribosome makes proteins. Prokaryotes have 70S ribosomes. Our ribosomes are 80 S. The ribosome is made up of proteins and RNA.

Our ribosomes are bigger because we have more proteins and rRNA. It reads the mRNA and forms peptide bonds between amino acids. Various stages of this process are inhibited or altered.

The major factor contributing to antibiotic resistance is the misuse of antibiotics.

Over 70% of the antibiotics produced in the United States are used in animal feed.

This is not present in mammalian cell = selective toxicity. Cancidas is used to treat infections caused by Candida and Pneumocystis.

Pneumocystis pneumonia is the number one cause of death in people that have AIDS.

i. We use cholesterol to adjust the fluidity of our membranes. Fungi use ergosterols. That gives us a target that is present only in fungi = selective toxicity.

Polyenes inhibit ergosterol synthesis and are fungicidal, but they are toxic to us and can cause damage to our kidneys Azols inhibit sterol synthesis and are also fungicidal.

Erythromycin bonds to the ribosome preventing translocation (the movement of the ribosome). Interestingly Erythromycin is absorbed by cells of the immune system and is secreted during active phagocytosis.

These cells therefore transport this antibiotic to the site of infection.

- Antimicrobial effectiveness can be categorized into 2 major groups.

a. Narrow spectrum antimicrobial agents only effect a small number of microbes (X: only Gram + or only Gram -). b. Broad spectrum antimicrobial agents are effective against multiple types of microbes. (X: both Gram + and Gram -).

- Selective toxicity is a desired characteristic in which the drug kills or inhibits microbial growth without harming your cells. This varies with the different antibiotics. - We measure the relative effects using the therapeutic index (TI).

a. The TI is a ratio between the effects of the drug on invaders and the effects of the drug on your cells. b. A large TI means that the drug does a lot of damage to the invader without harming your cells, so the larger the TI, the better for your normal cells.

- Alexander Fleming isolated penicillin from a fungus.

a. This was one of science's greatest accidental discoveries that saved thousands of lives when it was mass produced during WWII. Because of production problems, it took over a decade to be able to mass produce this antibiotic.

- Membrane: a. Candida albicans is a yeast that can cause oral thrush. This is common in very young and old people that are immunocompromised because this organism is an opportunistic pathogen (takes advantage of a weakened state). Oral thrush is common in people with HIV.

b. Mechanism of Action:

2. Spectrum: a. If you know the cause it is best to use a narrow spectrum antibiotic. This does the least damage to your normal flora.

b. Most doctors will incorrectly prescribe a broad spectrum antibiotic because they don't take the time to find the cause of the illness. This destroys your normal microbiota and leaves you susceptible to numerous pathogens like Candida albicans. This is the culprit behind vaginal yeast infections.

a.It is one of only a few antibiotics that can cross the blood-brain barrier.

b. One major side effect is aplastic anemia. Chloramphenicol reduces the number of blood cells produced by bone marrow and this eventually leads to a deficit.

a. Vancomycin is not absorbed orally so it must be given via IV if the infection is not in the digestive tract. b. It can be toxic to the ears and kidneys which is why it is not used frequently.

c. ACTIVITY: It works best on Gram + microbes. In most cases it is not active against most Gram - microbes. d. Vancomycin prevents peptide cross linking of the peptidoglycan which leads to a compromised cell wall.

i. Penicillin inhibits the growth of the bacterial cell wall b. Microbes have evolved an enzyme, β-lactamase, that inactivates these drugs by breaking this ring.

c. Penicillin works best on Gram positive (+) bacteria because they lack an outer membrane. Various improvements have been made to this drug to change its characteristics.

b. It binds to most membranes so it lacks selective toxicity. c. The thick cell wall of Gram + organisms does not allow this drug to gain access to the cell membrane so it has little effect on Gram + organisms.

d. It is bactericidal for Gram - organisms e. Found in neosporin

- Symptoms: a.VERY STINKY Diarrhea, collitis - Treatment: a. Fluids!!! b. DO NOT TAKE ANTI c. DIARRHEAL meds!!

d. Stop antibiotics (most cases) e. Specific antibiotics f. metronidazole (Flagyl) or Vancomycin - 2006 UTMB experienced a vancomycin resistant C-diff outbreak.

i. urinary tract, surgical wounds or the bloodstream d. Contraction: i. direct contact ii.Most common source: restroom door handle e. Preventative measures

i. Patient isolation ii.Gloves iii.Hand f. washing i. Good hygiene g. Treatment: combinations of Antibiotics

3. Tissue disruption, metabolism and excretion: a. To have any effect on the microbe, the antibiotic has to be distributed to the region of infection. i. Some antibiotics, if taken orally will not be absorbed so they are only useful for digestive tract infections.

ii. Others will be distributed to bone, skin or urinary bladder. Antibiotics can be metabolized and broken down. Others will be excreted and rapidly removed form the body. These characteristics must be considered when determining dosage and prescribing an appropriate antimicrobial agent.

c. Symptoms: i. abscesses and boils ii. septicemia

iii. toxic shock syndrome c. Treatment: Vancomycin i. Resistance is now here (VISA/VRSA