unit 3

Where antibiotics first came from

Naturally produced metabolic products of bacteria and fungi to reduce competition.

Kirby‑Bauer test

A disk diffusion test measuring zones of inhibition to determine susceptibility.

MIC (Minimum Inhibitory Concentration)

Lowest drug concentration that inhibits visible growth.

Narrow spectrum antibiotics

Target a specific group of bacteria.

Broad spectrum antibiotics

Effective against multiple groups of bacteria.

Therapeutic Index (TI)

Ratio of toxic dose : MIC. Higher TI = safer drug.

Antibiotics that target the cell wall

Penicillins, Cephalosporins, Carbapenems.

Antibiotics that target protein synthesis

Aminoglycosides, Tetracyclines, Glycylcyclines, Macrolides.

Antibiotics that target DNA/RNA

Fluoroquinolones → inhibit helicase.

Antibiotics that target folic acid

Sulfonamides.

Common antifungal drugs

Target ergosterol or fungal cell membrane; antibiotics don't work because fungi are eukaryotic.

Common antiprotozoal drugs

Metronidazole (Flagyl) - Giardia, Entamoeba, Trichomonas; Chloroquine/primaquine - malaria.

Common anti‑helminth drugs

Albendazole - inhibits glucose use; Pyrantel - paralyzes worms.

How drug resistance develops

Spontaneous mutation, Horizontal gene transfer (plasmids/R factors), Natural selection.

Role of plasmids in resistance

Carry R‑genes that can be transferred between bacteria.

Role of broad‑spectrum antibiotics in resistance

Kill normal flora → resistant strains survive and multiply.

New approaches to antimicrobial therapy

RNA interference, Defense peptides, CRISPR, Drugs from uncultivable bacteria, Bacteriophages, Probiotics / fecal transplants.

Hepatotoxic

Toxic to the liver.

Nephrotoxic

Toxic to the kidneys.

Neurotoxic

Toxic to the nervous system.

Superinfection

Overgrowth of resistant microbes after normal flora is destroyed.

Zoonosis

Infection transmitted from animals to humans.

Septicemia

Large numbers of multiplying microbes in the blood.

Bacteremia

Small numbers of bacteria in blood.

Viremia

Small numbers of viruses in blood.

True pathogen

Causes disease in healthy hosts.

Opportunistic pathogen

Causes disease when host defenses are compromised.

Endotoxins vs exotoxins

Reservoir

Primary habitat where a pathogen lives (soil, water, animals).

Carrier

Person who harbors and spreads pathogen without symptoms.

Vector

Arthropod that transmits infection (mosquito, tick).

Infectious dose (ID)

Minimum number of microbes needed to cause infection.

Leukopenia

Low WBC count.

Sequelae

Long‑term or permanent damage after infection.

Normal flora (normal biota)

Microbes that colonize the body long‑term and protect against pathogens.