Antimicrobial Drug
a chemical substance that destroys disease- causing microorganisms with minimal damage to host tissues
Chemotherapeutic agents
chemicals that combat diseases in the body
natural antibiotic 
a chemical compound produced by a microorganism that inhibits or kills other microorganisms at low concentrations
Semi-synthetic antibiotics 
chemically modified natural antibiotics; chemically modified organisms that inhibits or kills other microorganisms at low concentrations
synthetic organisms
wholly synthesized in the lab 
Reasons why natural antibiotics aren’t used in humans or animals

– poor uptake


Paul Ehrlich;

-developed the concept of chemotherapy as a way of treating microbial diseases

-predicted the development of chemotherapeutic agents that would kill pathogens without harming the host;

Alexander Fleming;

-discovered penicillin in 1929;

– however, clinical trails were not until the 1940s when Florey ; Chain used penicillin to prevent death from infection in the war ;

Selman Waksman
-isolates streptomycin in 1940s and proposed the term antibiotic
Natural Penicillins
-produced by the mold Penicillium are effective against gram-positive cocci and spirochetes
Semisynthetic Penicillins;

-are made in laboratory by adding different side chains (R groups) onto the B-lactam ring made by the fungus

-resistant to penicillinases and have a broader spectrum of activity than natural penicillin

The microbes that produce most of the antibiotics…


-sulfa drugs;

Problems of chemotherapy for viral, fungal, protozoan, and helminthic infections…

-antibacterial drugs effect many targets in the prokaryotic cell

-fungal, protozoan and helminthic infections are more difficult to treat because they are eukaryotic cells

Narrow-spectrum drugs

-affect only a select group of microbes

–ie: gram-positive cells

broad-spectrum drugs
-affect a large number of microbes; effective on both gram-negative and gram-positive bacteria 
hydrophillic drugs
-used to treat gram-negative cells
Antimicrobial agent
-a chemotherapeutic agent used to treat microbial infection;should not cause excessive harm to normal microbiota
-they are more effective when together
when taken together, both drugs become less effective than when taken alone
Five modes of action of antimicrobial drugs
see sheet
B- Lactam Antibiotic 


-cleaved between C=O and N

Why are these drugs specific for bacteria?
-They are anti-microbial drugs, so they only target bacteria

interferon proteins 


– a mode of action for antiviral drugs

Host cells produce these proteins that stop viral replication

-example= alpha-interferons that inhibit the spread of viruses to new cells


Nucleoside/ nucleotide analogs 

-a mode of action for a antiviral drugs 

-inhibit DNA or RNA synthesis

—-acyclovir, AZT, ddl and ddC


-a mode of action of antiviral drugs

-blocks penetration or uncoating of influenza A virus

Protease Inhibitors (PIs)

-a mode of antiviral drugs

-interfere with HIV maturation steps  

Antifungal Drugs: treatment of fungi

-selective toxicity is hard to achieve, but some chemotherapeutic agents are avaliable

-an emerging human health issue 

Antiprotozoan drugs 

-used to treat parasitic protozoan infections

-antimalarials, chloroquine, and quinacrine stop DNA synthesis by intercalation between base pairs


Antihelminthic drugs
-used to treat parasitic worms, Helminths
The disk-Diffusion Method/ Kirby-Bauer Test 

-filter paper disks impregnated with antibiotic are overlaid on a bacterial culture inoculated on an agar medium

-measured by a zone of inhibition


Zone of inhibition

-an absence of bacteria doesn’t grow due to the antibiotic

-a drug can be sensitive, intermediate, or resistant to the drug 


Minimum Inhibitory Concentration


-is the lowest concentration of chemotherapeutic agent capable of preventing microbial growth
Minimum Bacterial Concentration (MBC)
-the lowest concentration of chemotherapeutic agent that kills bacteria 
Broth Dilution Test 
-the microorganism is grown in a liquid media containing different concentrations of a chemotherapeutic agents 
Resistance Genes
R-factors that are chromosomal or carried by plasmids and transposons
occur when a pathogen develops resistance to the drug being used or when normally resistant microbiota multiply excessively 
New research for antimicrobial Drugs

-Computer drug design and new drug discovery

-analogs of exisiting drugs

-Chemicals produced by plants and animals are considered antimicrobial agents, including anitmicrobial peptides

-DNA complementary to specific DNA in pathogens 

holes within the cell and the cell eventually lyses and dies
diseases acquired from the hospital
Categories: Microbiology