ANTIMICROBIAL DRUGS

1928

Fleming discovered penicillin, produced by Penicillium.

ANTIMICROBIAL DRUGS

1940

Howard Florey and Ernst Chain performed first clinical trials of penicillin.

THE SPECTRUM OF ANTIMICROBIAL ACTIVITY

Narrow Spectrum of microbial activity

Range of different microbial types they affect; affects either gram-positive OR gram-negative bacteria; one or the other, but not both.

THE SPECTRUM OF ANTIMICROBIAL ACTIVITY

Broad-spectrum antibiotics

Antibiotics that affect a broad range of
gram-positive or gram-negative bacteria; both.

THE SPECTRUM OF ANTIMICROBIAL ACTIVITY

Superinfection

Growth of a target pathogen that has developed resistance to antibiotics; overgrowth; broad-spectrum antibiotic.

THE ACTION OF ANTIMICROBIAL DRUGS

Bactericidal

Kills microbes directly

THE ACTION OF ANTIMICROBIAL DRUGS

Bacteriostatic

Prevent microbes from growing; inhibits growth

MAJOR ACTION MODES OF ANTIMICROBIAL DRUGS

5 TYPES:

1. INHIBITION OF CELL WALL SYNTHESIS:
Penicillins, Cephalosporins, Bacitracin,
Vancomycin.

2. INHIBITION OF PROTEIN SYNTHESIS:
Chloramphenicol, Erythromycin, Tetracyclines,
Streptomycin.

3. INHIBITION OF NUCLEIC ACID REPLICATION AND
TRANSCRIPTION:
Quinolones, Rifampin.

4. INJURY TO THE PLASMA MEMBRANE:
Polymyxin B

5. INHIBITION OF ESSENTIAL METABOLITE
SYNTHESIS:
Sulfanimide, Trimethoprim.

ANTIMICROBIAL DRUGS

Para-aminobenzoic acid (PABA)

PABA is the substrate for an enzymatic reaction leading to the synthesis of folic acid, a vitamin that functions as a coenzyme for the synthesis of the purine and pyrimidine bases of nucleic acids and many amino acids.

INHIBITOR OF CELL WALL SYNTHESIS

Penicillin

A group of 50 chemically related antibiotics produced either by Penicillium (natural penicillins) or by adding side chains to the beta-lactam ring (semisynthetic penicillins); inhibitors of cell wall synthesis.

INHIBITOR OF CELL WALL SYNTHESIS

What are the three types of penicillins?

1. Natural penicillin

2. Semisynthetic penicillin

3. Extended-spectrum penicillin

INHIBITOR OF CELL WALL SYNTHESIS

Natural penicillin

Penicillin extracted from cultures of the mold Penicillium exists in several closely related forms.

INHIBITOR OF CELL WALL SYNTHESIS

What are the 2 types of natural penicillin?

1. Penicillin G:
against gram-positive bacteria,
*REQUIRES INJECTION.

2. Penicillin V:
against gram-positive bacteria,
*ORAL ADMINISTRATION.

INHIBITOR OF CELL WALL SYNTHESIS

Semisynthetic penicillins

Part of the penicillin is produced by the mold, and part is added synthetically; attempts to overcome the disadvantages of natural penicillins.

INHIBITOR OF CELL WALL SYNTHESIS

Extended-spectrum penicillins

Changes made to the narrow spectrum of activity of natural penicillins giving them a broader-spectrum making them effective against both gram-negative and gram-positive bacteria, although they are not resistant to penicillinases.

INHIBITOR OF CELL WALL SYNTHESIS

Augmentin

An approach to the proliferation of penicillinase to combine penicillins (Amoxicillin) with potassium clavulanate (clavulanic acid), which is a noncompetitive inhibitor of penicillinase with no antimicrobial activity of its own. It is a product of a Streptomycete; Penicillins + β-lactamase inhibitors (combo drug).

INHIBITOR OF CELL WALL SYNTHESIS

What are the 2 types of semisynthetic penicillins?

1. OXACILLIN:
narrow spectrum, only gram-positives, but
resistant to penicillinase.

2. AMPICILLIN:
Extended (broad)spectrum, many
gram-negatives.

β-LACTAM ANTIBIOTICS

Penicillin

1. Penicillinase-resistant penicillins.

2. Penicillins + β-lactamase inhibitors.

β-LACTAM ANTIBIOTICS

Carbapenems

Substitute a Carbon atom for a Sulfur and add a double bond to the penicillin nucleus.

β-LACTAM ANTIBIOTICS

Monobactam

A Single ring.

INHIBITOR OF CELL WALL SYNTHESIS

Cephalosporins: First Generation

Narrow spectrum; act against gram-positive bacteria.

INHIBITOR OF CELL WALL SYNTHESIS

Cephalosporins: Second Generation

Extended spectrum includes gram-negative bacteria

INHIBITOR OF CELL WALL SYNTHESIS

Cephalosporins: Third Generation

Includes pseudomonads; injected

INHIBITOR OF CELL WALL SYNTHESIS

Cephalosporins: Fourth Generation

Oral

INHIBITOR OF CELL WALL SYNTHESIS

Polypeptide antibiotics:

1. BACITRACIN:
topical application; against gram-positives

2. VANCOMYCIN:
glycopeptide; important "last line" against
antibiotic-resistant S. aureus.

INHIBITOR OF CELL WALL SYNTHESIS

Antimycobacterial antibiotics

1. ISONIAZID (INH):
inhibits mycolic acid synthesis.

2. ETHAMBUTOL:
inhibits incorporation of mycolic acid.

THE INHIBITION OF PROTEIN SYNTHESIS BY ANTIBIOTICS

30s subunit portions of the 70s prokaryotic ribosomes.

STREPTOMYCIN:
changes shape of 30s portion, causing code on
mRNA to be read incorrectly.

THE INHIBITION OF PROTEIN SYNTHESIS BY ANTIBIOTICS

50s subunit portions of the 70s prokaryotic ribosomes.

CHLORAMPHENICOL:
binds to 50s portion and inhibits formation of peptide bond.

THE INHIBITION OF PROTEIN SYNTHESIS BY ANTIBIOTICS

Tetracyclines

Interfere with attachment of tRNA to mRNA-ribosome complex.

THE INHIBITION OF PROTEIN SYNTHESIS BY ANTIBIOTICS

70s prokaryotic ribosome

Occurs in translation.

INHIBITORS OF PROTEIN SYNTHESIS

Chloramphenicol

Broad spectrum; binds 50s subunit; inhibits peptide bond formation.

INHIBITORS OF PROTEIN SYNTHESIS

Aminoglycosides

Streptomycin, Neomycin, Gentamicin; broad spectrum; change shape of 30s subunit.

INHIBITORS OF PROTEIN SYNTHESIS

Tetracyclines

Broad spectrum; interfere with tRNA attachment.

INHIBITORS OF PROTEIN SYNTHESIS

Glycylcyclines

MRSA and Acinetobacter baumanii; bind 30s subunit; inhibit translation.

INHIBITORS OF PROTEIN SYNTHESIS

Macrolides

Gram-positives; bind 50s subunit; prevent translocation.

INHIBITORS OF PROTEIN SYNTHESIS

Streptogramins

Gram-positives; bind 50s subunit; inhibit translation.

INHIBITORS OF PROTEIN SYNTHESIS

Oxazolidinones

Linezolid; MRSA; binds 50s subunit; prevent formation of 70s ribosome.

INHIBITORS OF PROTEIN SYNTHESIS

Pleuromutilins

From the mushroom Pleurotis Mutilus; MRSA; binds 50s; prevent translocation.

INJURY TO THE PLASMA MEMBRANE

Lipopeptides

Structural changes in the membrane, followed by arrest of the synthesis of DNA, RNA, and protein; MRSA.

INJURY TO THE PLASMA MEMBRANE

Polymyxin B

Topical; Combined with Bacitracin and Neomycin in over-the-counter preparation.

INHIBITORS OF NUCLEIC ACID SYNTHESIS

Rifamycin

Inhibits RNA synthesis; anti-tuberculosis.

INHIBITORS OF NUCLEIC ACID SYNTHESIS

Quinolones and Fluoroquinolones

Nalidixic Acid (urinary infections); Ciprofloxacin; Inhibit DNA gyrase; urinary tract infections.

COMPETITIVE INHIBITORS

Sulfonamides (sulfa drugs)

Inhibit folic acid synthesis; broad spectrum.

ACTIONS OF THE ANTIBACTERIAL SYNTHETICS TRIMETHOPRIM AND SULFAMETHOXAZOLE

Sulfamethoxazole

A Sulfonamide that is a structural analog of PABA, competitively inhibits the synthesis of Dihydrofolic Acid from PABA.

ACTIONS OF THE ANTIBACTERIAL SYNTHETICS TRIMETHOPRIM AND SULFAMETHOXAZOLE

Trimethoprim

A structural analog of a portion of Dihydrofolic Acid, competitively inhibits the synthesis of Tetrahydrofolic Acid.

ANTIFUNGAL DRUGS: INHIBITION OF ERGOSTEROL SYNTHESIS

Polyenes

Amphotericin B.

ANTIFUNGAL DRUGS: INHIBITION OF ERGOSTEROL SYNTHESIS

Azoles

Miconazole; Triazole.

ANTIFUNGAL DRUGS: INHIBITION OF ERGOSTEROL SYNTHESIS

Allylamines

For Azole-resistant infections.

ANTIFUNGAL DRUGS: INHIBITING CELL WALL SYNTHESIS

Echinocandins

Inhibit synthesis of β-glucan; Cancidas is used against Candida and Pneumocystis.

INHIBITION OF NUCLEIC ACIDS

Flucytosine

Cytosine analog interferes with RNA synthesis.

INHIBITION OF NUCLEIC ACIDS

Pentamidine isethionate

Anti-Pneumocystis; may bind DNA.

OTHER ANTIFUNGAL DRUGS

Griseofulvin

Inhibits microtubule formation; superficial dermatophytes.

OTHER ANTIFUNGAL DRUGS

Tolnaftate

Action unknown.

THE STRUCTURE AND FUNCTION OF THE ANTIVIRAL DRUG ACYCLOVIR

A) Acyclovir structurally resembles the nucleoside deoxyguanosine.

B) The enzyme thymidine kinase combines phosphates with nucleosides to form nucleotides, which are then incorporated into DNA.

C) Acyclovir has no effect on a cell not infected by a virus, that is, with normal thymidine kinase. In a virally infected cell, the thymidine kinase is altered and converts the acyclovir (which resembles the nucleoside deoxyguanosine) to a false nucleotide, which blocks DNA polymerase.

ANITVIRAL DRUGS

Protease inhibitors

Indinavir:
HIV

ANITVIRAL DRUGS

Integrase inhibitors

HIV

ANITVIRAL DRUGS

Entry inibitors

Amantadine:
influenza

ANITVIRAL DRUGS

Fusion inhibitors

1. Zanamivir:
influenza

2. Block CCR5:
HIV

ANITVIRAL DRUGS: INTERFERONS

1. Prevent spread of viruses to new cells.

2. Alpha interferon:
viral Hepatitis

ANITVIRAL DRUGS: INTERFERONS

Imiquimod

Promotes interferon production.

ANTIPROTOZOAN DRUGS

Chloroquine

Inhibits DNA synthesis; Malaria.

ANTIPROTOZOAN DRUGS

Artemisinin

Kills Plasmodium sporozoites.

ANTIPROTOZOAN DRUGS

Metronidazole

Interferes with anaerobic metabolism; Trichomonas an Giardia.

ANTIHELMINTHIC DRUGS

Niclosamide

Prevents ATP generation; tapeworms.

ANTIHELMINTHIC DRUGS

Praziquantel

Alters membrane permeability; flatworms.

ANTIHELMINTHIC DRUGS

Mebendazole and Albendazole

Interfere with nutrient absorption; intestinal roundworms.

ANTIHELMINTHIC DRUGS

Ivermectin

Paralysis of helminthes; intestinal roundworms.

ANTIBIOTIC RESISTANCE

1. A variety of mutations can lead to antibiotic
resistance.

2. Resistance genes are often on plasmids or
transposons that can be transferred between
bacteria.

BACTERIAL RESISTANCE TO ANTIBIOTICS

4 STEPS:

1. Blocking entry.

2. Inactivation by enzymes.

3. Alterations of target molecule.

4. Efflux of antibiotic.

ANTIBIOTIC RESISTANCE

Misuse of antibiotics

1. Misuse of antibiotics selects for resistance
mutants.

2. Misuse includes:
a) Using outdated or weakened antibiotics.

b) Using antibiotics for the common cold and
other inappropriate conditions.

c) Using antibiotics in animal feed.

d) Failing to complete the prescribed regimen

e) Using someone else's left over prescription.

EFFECTS OF COMBINATIONS OF DRUGS

Synergism

Occurs when the effect of two drugs together is greater than the effect of either one alone; work with each other.

EFFECTS OF COMBINATIONS OF DRUGS

Antagonism

Occurs when the effect of two drugs together is less than the effect of either one alone; work against each other.

ANTIBIOTIC SAFETY

Therapeutic index:
risk versus benefit

FUTURE CHEMOTHERAPEUTIC AGENT

Antimicrobial peptides

Broad spectrum antibiotics:
a) Nisin (lactic acid bacteria)

b) Defensins (human)

c) Magainin (frogs)

d) Squalamine (sharks)

FUTURE CHEMOTHERAPEUTIC AGENT

Phage therapy

GENE SILENCING COULD PROVIDE TREATMENTS FOR A WIDE RANGE OF DISEASES

4 STEPS:

1. An abnormal gene, cancer gene, or virus gene is
transcribed in a host cell.

2. siRNA binds mRNA.

3. RISC breaks down the RNA complex.

4. No protein expressions occur.

The first antibiotic discovered was:

Salvarsan.
Penicillin.
Quinine.
Streptomycin.
Sulfa drugs.

Penicillin.

Which of the following antibiotics inhibits cell wall synthesis?

Chloramphenicol
Trimethoprim
Rifampin
Cephalosporin
Erythromycin

Cephalosporin.

Which of the following antibiotics inhibits protein synthesis?

Vancomycin
Streptomycin
Rifampin
Cephalosporin
Isoniazid

Streptomycin.

Which of the following is not used for treating bacterial infections?

Methicillin
Griseofulvin
Rifampin
Ampicillin
Tetracycline

Griseofulvin.

Which antimicrobial works by inhibiting the synthesis of mycolic acid?

Methicillin
Penicillin
Vancomycin
Chloramphenicol
Isoniazid

Isoniazid.

Which of the following antibiotics should be prescribed as a first choice for a streptococcal infection?

Tetracycline
Amoxicillin
Trimethoprim
Rifampin
Neomycin

Amoxicillin.

Which of the following antibiotics inhibits folic acid synthesis?

Chloramphenicol
Ampicillin
Sulfanilamide
Neomycin
Tetracycline

Sulfanilamide.

Which of the following drugs inhibits the synthesis of mRNA in bacteria?

Polymyxin B
Ampicillin
Rifampin
Ethambutol
Trimethoprim

Rifampin.

Which of the following antibiotics frequently used as an alternative for those who are allergic to penicillin?

Ethambutol
Vancomycin
Erthryomycin
Streptomycin
Amoxicillin

Erthryomycin.

All of the following antibiotics inhibit protein synthesis except:

Erthromycin.
Bacitracin.
Tetracycline.
Chloramphenicol.
Streptomycin.

Bacitracin.

Which drug would be used to treat athlete's foot?

Amantadine
Neomycin
Clotrimazole
Polymyxin B
Chloroquine

Clotrimazole.

Which antifungal drug is commonly used for systemic fungal infections?

Clotrimazole
Tolnaftate
Miconazole
Fluconazole
Amphotericin B

Fluconazole.

Tetracyclines are effective against all of the following except:

Gram-negative bacteria.
intracellular chlamydias.
Gram-positive bacteria.
fungi.
intracellular rickettsias.

Fungi.

A nucleoside analog used to treat HIV infection is:

Ribavirin.
Zidovudine.
Praziquantel.
Acyclovir.
Amantidine.

Zidovudine.

All of the following are anti-protozoan drugs except:

Mefloquine.
Metronidazole.
Mebendazole.
Quinacrine.
Chloroquine.

Mebendazole.

Which drug is not a nucleoside analog?

Lamivudine
Zidovudine
Neviraprine
Acyclovir
Ribavirin

Neviraprine.

Which is the drug of choice for the treatment of malaria?

Iodoquinol
Flagyl
Quinacrine
Nifurtimox
Chloroquine

Chloroquine.

The drug, Flagyl, is commonly used to treat an STD caused by:

Trichomonas vaginalis.
Herpesvirus.
HIV.
Neisseria gonorrhoeae.
Treponema pallidum.

Trichomonas vaginalis.

Which of the following mechanisms is antifungal?

Inhibit ergosterol synthesis
Interfere with anaerobic metabolism
Cause muscle spasms
Inhibit peptidoglycan synthesis
Inhibit 70S ribosomes

Inhibit ergosterol synthesis.

Which of the following is used for treating influenza infections?

Indinivir
Acyclovir
Oseltamivir
Pentamidine isethionate
Interferon

Oseltamivir.

Antibiotic resistance can be minimized by the discriminating use of drugs in appropriate dosages.

True
False

True

The MIC is the lowest concentration of drug capable of preventing microbial growth.

True
False

True

It is relatively easy to find drugs that are effective against eukaryotic pathogens.

True
False

False

Bacteriostatic agents are ineffective as antibiotics.

True
False

False

Some drug combinations are antagonistic, therefore, when taken together they are more effective.

True
False

False

Semisynthetic penicillins are more effective antibiotics than natural penicillin.

True
False

True

In 1928, Alexander Fleming observed that the growth of the bacterium Staphylococcus aureus was inhibited by a mold thereby discovering the first antibiotic.

True
False

True

Because antifungal drugs like amphotericin B target sterols in the plasma membrane they are ineffective as antibacterial drugs.

True
False

True

Ivermectin is an anti-protozoan drug.

True
False

False

A drug that inhibits translation at 70S ribosomes can be used to treat human viral infections.

True
False

False

Which mode of antibiotic activity is the most selective target for antibiotics since it will not affect eukaryotic cells?

A) Inhibition of transcription
B) Inhibition of cell wall synthesis
C) Inhibition of translation
D) Inhibition of DNA replication
E) Injury to the plasma membrane

Inhibition of cell wall synthesis

Which of these antibiotics exerts its activity by changing the shape of 30S portion, causing the code on mRNA to be read incorrectly?

A) Tetracycline
B) Streptomycin
C) Erythromcyin
D) Chloramphenicol

Streptomycin

Which antibiotic pictured is not recommended for children due to possible discolorations of their teeth?

A) Penicillin
B) Amphotericin B
C) Tetracycline
D) Chloramphenicol

Tetracycline

All of the following are correct about the combination of trimethoprim and sufamethoxazole (TMP-SMZ) EXCEPT:

A) The combination reduces the emergence of
resistant strains.
B) The drugs in combination have a broad spectrum.
C) The drugs in combination are antagonistic.
D) When used together, less of the drugs are
needed, compared to when each drug is used
alone.

The drugs in combination are antagonistic.

Which of the following is correct about amphotericin B shown in the figure?

A) The drug belongs to the polyene group of
antifungals.
B) The drug is effective against gram-positive
bacteria only.
C) The drug has no side effects.
D) The drug targets protein synthesis.

The drug belongs to the polyene group of antifungals.

Which antibiotic shown in the figure appears to cause aplastic anemia in 1 in 500,000 individuals?

A) Penicillin
B) Amphotericin B
C) Erythromycin
D) Chloramphenicol
E) Streptomycin

Chloramphenicol

In the disk-diffusion assay shown in the photo, what do the clear areas around the discs represent?

A) It is impossible to determine from the
information given.
B) Where bacterial growth has been inhibited.
C) Where drug-resistant mutants are located.
D) Where the bacteria are growing the fastest.

Where bacterial growth has been inhibited.

FIGURE A

Which of the following chemical structures is of erythromycin? PICTURE A, B OR C

A) Figure a
B) Figure b
C) Figure c
D) None of these figures are of erythromcyin

Figure B

FIGURE B

SEE QUESTION 116

FIGURE C

SEE QUESTION 116

A disk-diffusion test identifies:

bacteriostatic agents.
agents to which a test culture is susceptible.
bactericidal agents.
MBC.

Agents to which a test culture is susceptible.

A chemical that kills gram-positive bacteria and gram-negative bacteria is described as:

selectively toxic.
inhibitory.
broad spectrum.
narrow spectrum.

Broad spectrum.

A drug that inhibits peptidoglycan synthesis is:

antibacterial.
antifungal.
antiprotozoal.
antiviral.

Antibacterial.

A drug that inhibits mitosis might be useful against all of the following infections except which type?

helminthic
protozoal
fungal
bacterial

Bacterial.

Clindamycin binds to the 50S ribosomal subunit to inhibit translocation. This antibiotic stops:

transcription in eukaryotes.
translation in prokaryotes.
transcription in prokaryotes.
translation in eukaryotes.

Translation in prokaryotes.

Gentamicin binds to the 30S ribosomal subunit to cause misreading of mRNA. This antibiotic stops:

transcription in prokaryotes.
translation in prokaryotes.
transcription in eukaryotes.
translation in eukaryotes.

Translation in prokaryotes.

A drug that binds with sterols would injure:

fungal cell walls.
eukaryotic plasma membranes.
bacterial cell walls.
DNA.

Eukaryotic plasma membranes.

The method of action of nucleoside analogs is:

disruption of plasma membrane.
inhibition of cell wall synthesis.
competitive inhibition.
inhibition of protein synthesis.

Competitive inhibition.

Ethambutol inhibits incorporation of mycolic acid into:

plasma membranes.
DNA.
enzymes.
cell walls.

Cell walls.

Ethambutol inhibits incorporation of mycolic acid, therefore it is effective against:

mycoplasmas.
gram-positive bacteria.
mycobacteria.
fungi.

Mycobacteria.

You have a 200 mg/ml antibiotic solution. You prepare serial dilutions (1:2, 1:4, etc.) of the antibiotic; the first tube contains 100 mg/ml. You then inoculate each tube with Salmonella. Bacteria grow in tubes 4, 5, and 6. You subculture bacteria from tubes 1 through 3 to nutrient broth. Growth occurs in the tube 3 subculture. You can conclude that the MIC is:

200 mg/ml.
cannot tell from the information provided.
25 mg/ml.
50 mg/ml.

25 mg/ml.

You have a 200 mg/ml antibiotic solution. You prepare serial dilutions (1:2, 1:4, etc.) of the antibiotic; the first tube contains 100 mg/ml. You then inoculate each tube with Salmonella. Bacteria grow in tubes 4, 5, and 6. You can conclude that the MBC is:

cannot tell from the information provided.
50 mg/ml.
12.5 mg/ml.
25 mg/ml.

Cannot tell from the information provided.

You have a 200 mg/ml antibiotic solution. You prepare serial dilutions (1:2, 1:4, etc.) of the antibiotic; the first tube contains 100 mg/ml. You then inoculate each tube with Salmonella. Bacteria grow in tubes 4, 5, and 6. You subculture bacteria from tubes 1 through 3 to nutrient broth. Growth occurs in tubes 2 through 3. You can conclude that the MBC is:

100 mg/ml.
12.5 mg/ml.
50 mg/ml.
25 mg/ml.

100 mg/ml.

Which one of the following pairs is not correctly matched?

Ciprofloxacin-inhibit cell wall synthesis
Defensin-makes membrane channels
RNAi-blocks protein synthesis
Griseofulvin-blocks microtubule formation

Ciprofloxacin-inhibit cell wall synthesis.

You obtain the following zones of inhibition (ZI) from a disk-diffusion test on Staphylococcus aureus. Antibiotic A, ZI = 0 mm; Antibiotic B, ZI = 23 mm; Antibiotic C, ZI = 16 mm. Which antibiotic is bacteriostatic?

cannot tell from the information provided
antibiotic C
antibiotic A
antibiotic B

Cannot tell from the information provided.

Rifampin blocks RNA polymerase to inhibit:

transcription.
translation.
DNA synthesis.
cell wall synthesis.

Transcription.

Antisense DNA will combine with a pathogen's DNA to:

inhibit translation.
inhibit cell wall synthesis.
inhibit peptide bond formation.
inhibit transcription.

Inhibit transcription.

Polyenes, azoles, and allyamines interfere with sterol synthesis. These drugs will affect:

fungi.
gram-positive bacteria.
viruses.
gram-negative bacteria.

Fungi.

Which of the following statements is true about superinfections?

They are caused by endospore-forming bacteria.
They are caused by antibiotic-resistant
bacteria.
They only occur in people with
immunodeficiencies.
They inhibit protein synthesis.

They are caused by antibiotic-resistant bacteria.

Sulfa drugs are selective against bacteria for all of the following reasons except which?

Bacteria synthesize folic acid.
Sulfa drugs inhibit a bacterial enzyme.
Humans have a dietary requirement for folic
acid.
Sulfa drugs cause production of
antimetabolites.

Sulfa drugs cause production of antimetabolites.