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This document is a study guide on microorganisms found in food, covering learning objectives, characteristics of different microorganisms, study questions related to bacteria, and temperature growth ranges of psychrotrophs and mesophiles.

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# Lesson 1 Study Guide ## Learning Objectives: 1. List the different types of microorganisms found in foods 2. Compare and contrast the cellular characteristics and means of replication of different microorganisms 3. Correctly apply microbial naming conventions 4. Distinguish between microbial tax...

# Lesson 1 Study Guide ## Learning Objectives: 1. List the different types of microorganisms found in foods 2. Compare and contrast the cellular characteristics and means of replication of different microorganisms 3. Correctly apply microbial naming conventions 4. Distinguish between microbial taxonomy levels 5. Describe the characteristics used to categorize bacteria 6. Categorize microorganisms based on whether they can grow, survive, and/or die in foods 7. Distinguish between harmful and non-harmful microorganisms in foods ## Table 1: Characteristics of Different Microorganisms Found in Foods | Category | Bacteria | Yeast | Mould | Viruses (Both Human Viruses and Bacteriophages) | Parasites | |---|---|---|---|---|---| | **Cell Type (e.g. prokaryote, eukaryote)** | Prokaryote | Eukaryote | Eukaryote | Acellular | Eukaryote | | **Single or Multicellular** | Single | Single | Multicellular | None | Single = Protozoa, Multi = Helminths | | **Can They Grow in Foods? (Y, N)** | Y | Y | Y | N | N | | **Good (Y, N)** | Y | Y | Y | N | N | | **Bad (Y, N)** | Y | Y | Y | N | N | | **Ugly (Y, N)** | Y | N | Y | Y | Y | | **Reproduction Mechanism** | Binary Fission (Asexual Reproduction) | Budding (Asexual Reproduction) | Produces Spores (Asexual Reproduction) | Replication Inside Host Cells (Lytic) | Reproduces Inside Host Organisms | ## Study Questions 1. Can bacteria have more than one plasmid? - Yes, bacteria can have one or more plasmids. Plasmids are small, extrachromosomal DNA molecules that can contain additional genes beneficial under specific conditions → antimicrobial resistance. 2. What types of genes are contained on chromosomes vs. plasmids? - **Chromosomes:** Contain ALL essential genes required for normal survival and reproduction under typical conditions. - **Plasmids:** Contain additional, non-essential genes that provide advantages, such as antimicrobial resistance, virulence factors, or the ability to metabolize unusual substances, GFP. 3. What are the various growth phases of bacteria and what happens in each state? - **Lag Phase:** Little or no increase in cell number as bacteria adapt to their environment and synthesize necessary enzymes. - **Log Phase:** Exponential growth where bacteria divide at the fastest possible rate for the given conditions. - **Stationary Phase:** Growth rate equals death rate as nutrients are depleted, and waste products accumulate. - **Death Phase:** Death rate exceeds growth rate due to exhaustion of resources and accumulation of toxic by-products. 4. What is the maximum level of bacteria that can be achieved in foods? - In a nutritionally rich environment, bacteria can reach a maximum density of approximately 9 log CFU/mL (109 CFU/mL). 5. What are the main differences in the cell wall of Gram-positive and Gram-negative bacteria? Which color will these bacteria stain after Gram staining and why? - **Gram-positive:** Thick peptidoglycan cell wall that retains the crystal violet stain, appearing purple. - **Gram-negative:** Thin peptidoglycan layer surrounded by an outer membrane with lipopolysaccharides. It does not retain the violet stain and appears pink. 6. What are the temperature growth ranges for psychrotrophs and mesophiles? What are their optimal growth temperatures? - **Psychrotrophs:** Grow between 0°C and 30°C; optimal around 20°C to 30°C. - **Mesophiles:** Grow between 20°C and 45°C; optimal around 37°C. 7. What is the difference between psychrophiles and psychrotrophs? - **Psychrophiles:** Thrive in extremely cold temperatures, with an optimal growth range of -5°C to 15°C. - **Psychrotrophs:** Grow in cold environments but can also grow at higher temperatures, typically up to 30°C. 8. What is the difference between microaerophiles and aerotolerant anaerobes? - **Microaerophiles:** Require low levels of oxygen to grow but are inhibited by higher concentrations. - **Aerotolerant anaerobes:** Do not use oxygen but can survive and grow in its presence. 9. Which temperature and oxygen requirements categories do most pathogenic foodborne bacteria belong to? - **Temperature:** Mesophiles (optimal growth at ~37°C, human body temperature). - **Oxygen requirement:** Facultative anaerobes (can grow with or without oxygen). 10. When do bacteria form endospores? When do spores break and bacteria return to being vegetative cells? - **Formation:** Bacteria form endospores in response to harsh conditions, such as low nutrients, extreme temperatures, or chemical damage. - **Sporulation breaks:** When environmental conditions improve, the spores germinate, and the bacteria return to their vegetative state. 11. Can bacterial spores replicate? - No, bacterial spores are metabolically dormant and cannot replicate until they germinate into vegetative cells. 12. What are the different functions of bacterial flagella? - Movement toward nutrients (chemotaxis). - Movement away from harmful substances (negative chemotaxis). - Attachment to human cells (infection) or inanimate surfaces (biofilm formation). - Facilitating movement between and within human cells during infection. - Assisting in protein export. 13. Do facultative anaerobes grow faster in aerobic or anaerobic conditions? - Facultative anaerobes grow faster in aerobic conditions because oxygen allows them to generate more ATP through aerobic respiration compared to fermentation or anaerobic respiration. 14. What is the difference between binary fission and mitosis? - **Binary fission:** Asexual reproduction in prokaryotes where the single circular chromosome replicates, and the cell splits into two identical daughter cells. - **Mitosis:** Cell division in eukaryotes that involves multiple chromosomes and distinct stages (prophase, metaphase, anaphase, telophase) for accurate chromosome segregation. 15. How does the number of chromosomes differ between prokaryotic and eukaryotic cells? - **Prokaryotes:** Typically have one single, circular chromosome. - **Eukaryotes:** Have multiple, linear chromosomes contained within a nucleus. 16. Do viruses have a chromosome(s)? Explain? - Viruses do not have traditional chromosomes. Instead, they contain genetic material in the form of either DNA or RNA enclosed in a protein capsid. 17. What is a prophage and why does it pose food safety risks? - A prophage is the viral DNA that integrates into a bacterial genome during the lysogenic cycle of a bacteriophage. Prophages can carry genes that encode toxins (e.g., Shiga toxin in E. coli), antimicrobial resistance, or other virulence factors, making bacteria more pathogenic. ## Also Know: 1. **Order of Taxonomy Levels** - Domain - Kingdom - Phylum - Class - Order - Family - Genus - Species - **Dear King Philip Came Over For Good Soup** 2. **Generation Time Calculations** - Number of cells = initial number of cells x 2 Number of generations

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