Antibiotic Sensitivity Testing and Types of Chemotherapeutic Agents Quiz

Antibiotic Sensitivity Test

• Antibiotic sensitivity test is a standardized method to measure the effectiveness of antibiotics and chemotherapeutic agents on pathogenic microorganisms.
• It is essential for describing appropriate treatment.

Types of Antibiotics

• Antibiotics: Produced by some microbes naturally as a by-product of their metabolic activities, and have the ability to inhibit or kill other types of microbes (e.g., Penicillin and Cephalosporin).
• Synthetic agents: Completely synthesized in laboratories by chemical processes unrelated to microbial activity (e.g., Ciprofloxacin).
• Semi-synthetic agents: Natural antibiotics that have been chemically modified (e.g., Ampicillin).

Mechanisms of Action of Antibiotics

• Inhibit cell wall synthesis (e.g., Penicillin).
• Inhibit cytoplasmic membrane (e.g., Colistin).
• Inhibit protein synthesis (e.g., Tetracycline).
• Inhibit nucleic acid synthesis (e.g., Rifamycin).
• Inhibit folic acid synthesis (e.g., Sulfonamides).

Spectrum of Action

• Narrow spectrum drugs: Effect against only a few kinds of pathogens (e.g., Penicillin, affecting only gram-positive bacteria).
• Broad spectrum drugs: Effect against many different kinds of pathogens (e.g., Ampicillin).

Microbial Culture Test

• Demonstration of pathogenic organisms in the patient specimen is the most definitive test in microbiology.
• Many bacteria, fungi, parasites, and viruses can be grown in a lab when appropriate conditions are used.
• Common specimens include blood, urine, sputum, stool, pus, and swabs (throat, nasal, ear, eye, and cervical).

Routine Microbiology Specimen Collection Procedures

• Obtain complete patient information, including name, source of specimen, collection date, and test desired.
• Collect specimens correctly, using a sterile container and labeling correctly.
• Avoid contamination of the container and send the specimen to the laboratory promptly.

Antibiotic Sensitivity Test Results

• Sensitive: Clear, circular "halo" (zone of inhibition) appears around the antibiotic disk, indicating the antibiotic has inhibited bacterial growth and killed them.
• Intermediate: Somewhat cloudy zone indicates some bacteria are sensitive to the antibiotic, while others are genetically immune.

Fungal Culture

• 30°C is the optimal temperature for isolating fungi from clinical specimens.
• Dimorphic fungi are cultured at 30°C for the growth of mold form and 37°C for the growth of yeast form.
• Colony characteristics include color, texture, and rate of growth.
• Microscopic examination of culture includes septate or aseptate hyphae, hyaline or dematiaceous hyphae, fruiting structures, and conidia.

Identification of Culture

• Colony characteristics include color, texture, and rate of growth.
• Microscopic examination of culture includes septate or aseptate hyphae, hyaline or dematiaceous hyphae, fruiting structures, and conidia.

Biochemical Tests

• Ornithine decarboxylase (ODC): Converts ornithine to putrescine, raising the pH and changing the color from yellow to red.
• Citrate (CIT): Utilization of citrate as a source of carbon results in a change in the pH and a change in the color from green to blue.
• H2S production: Reacts with iron to form a black precipitate.
• URE: Tests for the enzyme urease, which consumes urea to produce ammonia and changes the color from yellow to red.
• Tryptophan deaminase (TDA): Consumes tryptophan to produce indole and pyruvic acid, and in the presence of iron chloride, a red-brown color is formed.
• Indole Test (IND): Detects production of indole from tryptophan by the enzyme tryptophanase.
• Voges-Proskauer test (VP): Detects acetone produced by fermentation of glucose by bacteria.
• GEL: Tests for the production of the enzyme gelatinase, which liquefies gelatin and produces a black color.
• Consumption of carbohydrates: Produces acid that changes the color of the index from blue to yellow.