Microbiology Unit 4/Final Exam Study Guide

Important Vocabulary in Microbiology

Key Terms and Definitions

This section covers essential vocabulary for understanding microbial control, antimicrobial agents, and molecular biology techniques relevant to microbiology.

• Sterilization: The process of eliminating all forms of microbial life, including spores, from an object or environment.

• Disinfection: The use of chemical or physical agents to destroy or inhibit most microorganisms on inanimate objects.

• Antisepsis: Application of antimicrobial agents to living tissue to reduce the possibility of infection.

• Pasteurization: Heat treatment that kills pathogens and reduces spoilage organisms in food and beverages.

• Bacteriostatic: Agents that inhibit the growth and reproduction of bacteria without killing them.

• Bactericidal: Agents that kill bacteria.

• Sepsis: The presence of harmful microorganisms or their toxins in tissues, typically causing infection.

• Thermal death point: The lowest temperature at which all microbes in a sample are killed in 10 minutes.

• Thermal death time: The minimum time required to kill all microorganisms at a given temperature.

• Non-perishable: Foods or items that do not spoil or decay easily due to microbial activity.

• Antimicrobial: Any substance that kills or inhibits the growth of microorganisms.

• Antibiotic: A chemical substance produced by microorganisms that can inhibit or kill other microbes.

• Broad spectrum: Antimicrobials effective against a wide range of microorganisms.

• Osmotic pressure: The pressure exerted by solutes in solution, used to control microbial growth by dehydration.

• Beta-lactam: A class of antibiotics (e.g., penicillins) that inhibit cell wall synthesis.

• Nucleoside analog: Molecules that mimic natural nucleosides and interfere with DNA/RNA synthesis.

• Communicable disease: Diseases that can be transmitted from one host to another.

• Horizontal gene transfer: Movement of genetic material between organisms other than by descent.

• Vector: An organism or vehicle that transmits pathogens or genetic material.

• Clavulanic acid: A beta-lactamase inhibitor used to enhance the effectiveness of beta-lactam antibiotics.

• Restriction endonuclease: Enzymes that cut DNA at specific sequences, used in molecular cloning.

• Annealing: The binding of complementary nucleic acid strands, especially in PCR.

• Competence: The ability of a cell to take up foreign DNA from its environment.

• Denaturation: The process of separating double-stranded DNA into single strands, often by heat.

• Extension: The synthesis of new DNA strands by DNA polymerase during PCR.

• Replication: The process of copying DNA before cell division.

• Carbon cycle: The movement of carbon through biological systems.

• Nitrogen cycle: The movement of nitrogen through the environment and living organisms.

• Sulfur cycle: The movement of sulfur through the biosphere.

• Topsoil: The uppermost layer of soil, rich in organic material and microorganisms.

• Bedrock: The solid rock layer beneath soil, not typically involved in microbial processes.

Control of Microbial Growth

Physical Methods

Physical methods are used to reduce or eliminate microbial populations in various environments and materials.

• Heat: Includes moist heat (autoclaving, boiling) and dry heat (oven sterilization).

• Filtration: Removal of microbes from liquids or air using physical barriers.

• Radiation: Use of ionizing (gamma rays) or non-ionizing (UV light) radiation to damage microbial DNA.

• Osmotic pressure: High concentrations of salt or sugar create hypertonic environments that inhibit microbial growth.

• Desiccation: Drying removes water, preventing microbial metabolism.

Example: Autoclaving is commonly used to sterilize laboratory equipment by applying high-pressure steam.

Chemical Methods

Chemical agents are used to disinfect, sterilize, or preserve materials by killing or inhibiting microbes.

• Alcohols: Denature proteins and disrupt membranes (e.g., ethanol, isopropanol).

• Halogens: Oxidize cellular components (e.g., chlorine, iodine).

• Phenolics: Disrupt cell walls and membranes.

• Quaternary ammonium compounds: Disrupt membranes.

• Heavy metals: Inactivate proteins (e.g., silver, mercury).

• Aldehydes: Cross-link proteins and nucleic acids (e.g., formaldehyde).

Example: Chlorine is used to disinfect drinking water and swimming pools.

Extending Shelf Life of Food

Controlling microbial growth is essential for food preservation and safety.

• Canning: Seals food in airtight containers and heats to destroy microbes.

• Pasteurization: Reduces microbial load in liquids without affecting taste.

• Drying and dehydration: Removes water to inhibit microbial metabolism.

• Use of preservatives: Salt, sugar, and chemical additives inhibit microbial growth.

Example: Jam and salted meats are preserved by high sugar or salt concentrations, which inhibit microbial growth.

Antimicrobials and Antibiotics

Mechanisms of Action

Antimicrobials target specific structures or processes in microbes to inhibit or kill them.

• Cell wall synthesis inhibitors: e.g., beta-lactams (penicillins, cephalosporins).

• Protein synthesis inhibitors: e.g., tetracyclines, aminoglycosides.

• Nucleic acid synthesis inhibitors: e.g., quinolones, nucleoside analogs.

• Metabolic pathway inhibitors: e.g., sulfonamides.

• Membrane disruptors: e.g., polymyxins.

Example: Clavulanic acid is used with amoxicillin to inhibit beta-lactamase enzymes produced by resistant bacteria.

Bacterial vs. Viral Infections

Bacterial infections are generally easier to treat than viral infections due to differences in cell structure and replication.

• Bacteria: Have cell walls and metabolic pathways targeted by antibiotics.

• Viruses: Lack cellular structures; require host cells for replication, making them harder to target without harming host.

Example: Antibiotics are ineffective against viruses such as influenza or HIV.

Nucleoside Analogs

Nucleoside analogs mimic natural nucleosides and interfere with DNA or RNA synthesis, often used as antiviral drugs.

• Mechanism: Incorporated into viral DNA/RNA, causing chain termination or mutations.

• Example: Acyclovir is used to treat herpesvirus infections.

Molecular Biology Techniques

Polymerase Chain Reaction (PCR)

PCR is a technique used to amplify specific DNA sequences for analysis or cloning.

• Steps:

  1. Denaturation: DNA is heated to separate strands.

  2. Annealing: Primers bind to target sequences.

  3. Extension: DNA polymerase synthesizes new DNA strands.

• Key components: Template DNA, primers, DNA polymerase (e.g., Taq polymerase), nucleotides.

Example: PCR is used in forensic science to amplify DNA from crime scenes.

Equation:

$N = N_0 \times 2^n$

Where $N$ is the number of DNA copies after $n$ cycles, starting from $N_0$ template molecules.

Restriction Endonucleases and Cloning Vectors

Restriction enzymes cut DNA at specific sequences, enabling genetic engineering and cloning.

• Cloning vectors: DNA molecules (often plasmids) used to carry foreign DNA into host cells.

• Markers: Genes (e.g., antibiotic resistance) used to identify cells that have taken up the vector.

Example: Plasmids with multiple restriction sites are used to insert and express foreign genes in bacteria.

Vaccines and Disease Prevention

Types of Vaccines

Vaccines stimulate the immune system to protect against infectious diseases.

• Live attenuated: Weakened forms of the pathogen.

• Inactivated: Killed pathogens.

• Subunit: Specific components of the pathogen (e.g., proteins).

• Recombinant: Produced using genetic engineering.

Example: Gardasil is a recombinant vaccine protecting against human papillomavirus (HPV).

Food Preservation Methods

Common Techniques

Preserving food involves inhibiting microbial growth to prevent spoilage and disease.

• Canning: Seals food and applies heat to destroy microbes.

• Pasteurization: Reduces microbial load in liquids.

• Drying: Removes water to inhibit growth.

• Gamma radiation: Destroys microbes by damaging DNA.

• Lyophilization: Freeze-drying preserves food and biological samples.

Role of Sugar and Salt

Sugar and salt act as preservatives by creating hypertonic environments that inhibit microbial growth.

• Mechanism: High osmotic pressure draws water out of microbial cells, preventing metabolism.

• Example: Salted fish and jams are preserved by high salt or sugar concentrations.

Potable Water

Definition and Safety

Potable water is water that is safe to drink because it is free from harmful microorganisms and contaminants.

• Criteria: Must be free of pathogens, toxins, and excessive chemical contaminants.

• Example: Municipal water supplies are treated and tested to ensure potability.

Sample Multiple Choice Questions (MCQs)

Representative Questions

These questions test understanding of microbial control, molecular biology, and disease prevention.

• What are the physical methods used to control microbial growth? (Give examples)

• What are the chemical methods used to control microbial growth? (Give examples)

• Which methods of controlling microbial growth have we used to extend the shelf life of our food sources?

• Why did Kary Mullis win a Nobel prize? Additional info: For inventing the polymerase chain reaction (PCR).

• How does a PCR work?

• What are the mechanisms of action of various antimicrobials?

• Which is harder to treat: a bacterial infection or a viral infection? Why?

• How do nucleoside analog drugs work?

• What type of vaccine is Gardasil?

• Which of the following diseases capable of being weaponized have a vaccine available? (Plague, Smallpox, Anthrax)

• Which of the following statements regarding vectors is FALSE?

• Which of the following is essential in PCR? (DNA polymerase, DNA primers, etc.)

• If a researcher used Escherichia coli DNA polymerase instead of Thermus aquaticus DNA polymerase in the PCR procedure, what would be the result? Additional info: Taq polymerase is heat-stable; E. coli polymerase would denature during the high-temperature steps.

• Which of the following methods of preserving food sterilizes it? (Canning, Pasteurization, Drying, Gamma radiation, Lyophilization)

• Sugar and salt act as preservatives by __________.

• Potable water is water that __________.

Comparison Table: Physical vs. Chemical Methods of Microbial Control

Method Type	Examples	Main Mechanism
Physical	Heat (autoclaving, boiling), Filtration, Radiation, Desiccation, Osmotic pressure	Destroys or removes microbes by physical means
Chemical	Alcohols, Halogens, Phenolics, Quaternary ammonium compounds, Heavy metals, Aldehydes	Disrupts cellular components or metabolic processes

Summary

This study guide covers the essential vocabulary, concepts, and techniques for controlling microbial growth, understanding antimicrobials, and applying molecular biology in microbiology. It also provides representative questions and a comparison table to aid exam preparation.