Microbial Growth Control Chapter 13

Unit 3: Control of Microorganisms

Section 1: Chapter 13 – Control of Microbial Growth

• Resistance to Microbial Control: Prions and bacterial endospores are the most resistant, followed by bacteria (like Mycobacteria), zygospores, and naked viruses. Fungal spores, hyphae, and yeasts are least resistant.

• Key Terms:

• Fomite: Object transmitting disease.

• Sterilization: Complete removal of all living microbes.

• Sanitization: Reduces microbes to safe levels.

• Disinfection: Kills pathogens on nonliving surfaces.

• Asepsis: Killing pathogens on living tissue.

• Aseptic technique: Prevents contamination of sterile surfaces.

• Degerming: Mild chemicals + scrubbing to reduce microbes on living tissue.

• -cide: Kills organisms.

• -static: Inhibits growth.

• Microbial death: Permanent loss of reproductive capability.

• Microbial death curve: Graph of microbial control progress.

• Decimal Reduction Time (D-value): Time to kill 90% of a population.

• Thermal death time: Minimum time to kill the entire population at a specific temperature.

• Incineration: Destruction by direct flame.

• Physical Control Methods:

• Heat: Oxidizes cellular components (e.g., autoclaving, boiling).

• Boiling: 100°C for lab prep and personal use.

• Dry heat oven: 170°C for 2 hours to sterilize lab equipment.

• Incineration: Burns microorganisms.

• Autoclave: 121°C for 15 minutes, sterilizes media and equipment.

• Pasteurization: Prevents spoilage in food.

• Cold: Reduces microbial metabolic rate.

• Freezing: Long-term storage at -2°C.

• Refrigeration: Short-term storage at 0-7°C.

• Desiccation (Dehydration): Removes moisture.

• Lyophilization: Rapid freezing under vacuum for preservation.

• Radiation:

• Ionizing: Gamma rays, sterilizes items, food, and spices.

• Non-ionizing: UV rays for sterilizing lab materials and water.

• Filtration: Removes microorganisms from liquids or gases.

• HEPA filters: Trap particles, organisms, and spores from air.

• Membrane filters: Used in vaccine production.

• Factors Affecting Bacterial Growth: Temperature, pH, moisture, nutrient availability, oxygen, and other environmental factors.

• Monitoring Autoclave Effectiveness: Autoclave tape: strips change color to indicate successful sterilization.

• Chemical Antimicrobial Agents:

• Phenolics: Denature proteins, disrupt membranes (e.g., Lysol).

• Metals: Bind to proteins, inhibit enzymes (e.g., mouthwash).

• Halogens: Oxidize macromolecules (e.g., bleach).

• Alcohols: Denature proteins, disrupt membranes (e.g., hand sanitizers).

• Peroxides: Oxidize cellular components (e.g., hydrogen peroxide).

• Aldehydes: Inactivate viruses, destroy bacterial cells (e.g., formaldehyde).

• Detergents: Surfactants disrupting membranes.

• Gases: Sterilize materials like paper, plastics (e.g., ethylene oxide).

• Evaluation of Disinfectants/Antiseptics:

• Phenol coefficient: Compares disinfecting ability to phenol.

• Disk diffusion: Chemicals applied to filter paper disks.

• Use dilution test: Exposures of cultures to chemical agents.

• In-use test: Use of diluted disinfectant on agar.

Section 2: Chapter 14 – Antimicrobial Drugs

• Key Scientists:

• Paul Ehrlich: First synthetic antimicrobial (arsphenamine).

• Gerhard Domagk: Discovered prontosil (synthetic antimicrobial dye).

• Alexander Fleming: Discovered penicillin from Penicillium mold.

• Florey and Chain: Demonstrated penicillin's effectiveness.

• Types of Antimicrobial Drugs:

• Synthetic drugs: Lab-made (e.g., prontosil).

• Antibiotics: Naturally occurring agents that kill/inhibit organisms (e.g., penicillin).

• Semi-synthetic: Chemically modified for enhanced activity.

• Antibiotic Spectrum:

• Narrow spectrum: Targets one group (e.g., penicillin).

• Broad spectrum: Affects multiple groups (e.g., tetracycline).

• Drug Administration:

• Dosage: Amount of medication.

• Route: Method of introduction (oral, topical, parenteral).

• Chemotherapeutic Index: Ratio of toxic dose to therapeutic dose.

• Antibiotic Targets and Classes:

• Cell wall: B-lactams, Glycopeptides, Bacitracin.

• Protein synthesis: Polymyxins, Lipopeptides.

• Ribosomes: 30S and 50S subunits (e.g., aminoglycosides, tetracyclines).

• Metabolic pathways: Folate synthesis (e.g., sulfonamides, trimethoprim).

• DNA synthesis: Fluoroquinolones.

• RNA synthesis: Rifamycins.

• Antibiotic Resistance Mechanisms:

• Drug modification: Enzyme inactivates the antibiotic.

• Prevention of uptake: Drug doesn't enter or is pumped out.

• Target modification: Altered binding site.

• Minimum Inhibitory Concentration (MIC): Lowest drug concentration inhibiting visible growth.

• Susceptibility Assays:

• Disk diffusion: Apply chemicals to paper disks.

• Tube dilution: Determine MIC by serial dilution.

• Microdilution tray: Test MIC using microplates.

• E-test: Determine MIC using a gradient strip.

Unit 4 Section 1: Unicellular Eukaryotic Parasites (Protozoa)

Section 2: Chapter 5.2: Helminths

• Helminths: Parasitic worms causing diseases. Two main types: Roundworms (Nematodes) and Flatworms (Platyhelminthes).

• Flatworms (Platyhelminthes): Flat, soft-bodied, often segmented, and lack a digestive system (absorb nutrients through skin).

• Trematoda (Flukes): Flattened, leaf-shaped, nonsegmented; have mouth and suckers for attachment; transmitted by walking in infected water; cause diseases like schistosomiasis.

• Cestoda (Tapeworms): Long, segmented bodies; no mouth, absorb nutrients; transmitted by eating undercooked meat; cause tapeworm infections.

• Cestoda Structures:

• Proglottids: Segments containing reproductive organs.

• Scolex: The head with suckers and/or hooks for attachment.

• Trematode Life Cycle: Miracidia (free-swimming larva) infects snail, develops into cercariae.

• Nematode Life Cycle: Rhabditiform larva in host digestive system, develops into filariform larva.

• Helminth Diseases and Treatments:

• Pinworm: Enterobius vermicularis, transmitted by contaminated surfaces, itchy anus; treated with mebendazole or albendazole.

• Trichinellosis: Trichinella spiralis, from undercooked pork/wild game, abdominal and muscle pain; treated with mebendazole or albendazole.

• Ascariasis: Ascaris lumbricoides, from contaminated soil/food, abdominal pain, coughing; treated with mebendazole or albendazole.

• Necatoriasis (Hookworm): Necator americanus, from skin contact with contaminated soil, itchy rash, anemia; treated with mebendazole or albendazole.

• Elephantiasis (Lymphatic Filariasis): Wuchereria bancrofti, from mosquito bite, swelling of limbs/genitals; treated with ivermectin or diethylcarbamazine.

• Schistosomiasis (Blood Fluke): Schistosoma species, from contact with contaminated water, fever, abdominal pain; treated with praziquantel.

• Antihelminth Agents: Praziquantel (trematodes/cestodes), mebendazole (nematodes), avermectin, ivermectin (nematodes).