MMG Short answers

1. Your patient is prescribed a new antibiotic for a urinary tract infection. They ask, "Is this going to kill all the bacteria in my body?" Using patient-friendly language, write a short explanation distinguishing pathogens from normal microbiota and give one example of how the microbiome benefits health.

• No, the antibiotic will not kill all the bacteria in your body. It is prescribed to target the pathogen causing your UTI, while many of the bacteria that normally live in your body should remain.

• Pathogens are microorganisms that can cause disease, while normal microbiota are microorganisms that normally live on and in your body, including mutualistic or commensal bacteria, archaea, and eukaryotic microbes like protists, and usually have a beneficial or neutral relationship with you.

• Normal microbiota train your immune system, produce vitamins, and help digest food.

  • For example, gut microbes help break down food that your digestive system cannot fully break down, helping your body obtain additional nutrients and calories.

• Antibiotics target the bacteria causing the infection, but they cannot always fully distinguish between harmful and beneficial bacteria, so they may also kill some of the normal microbiota. This can temporarily disrupt the balance of bacteria in the microbiome, called dysbiosis, but it does not mean that all the bacteria in your body are killed.

2. A patient develops a wound infection caused by Clostridium perfringens (an endospore-forming bacterium). Describe/define endospore. Explain why endospores are medically significant. Describe how they influence infection control measures in the hospital. (6 points)

• Endospore: A dormant, highly resistant structure formed by certain bacteria, especially Clostridium and Bacillus, when environmental conditions become unfavorable or harsh.

• When conditions are poor, the bacterial cell forms an endospore that allows it to survive harsh conditions and survive outside of the host. Endospores can resist drying, freezing, radiation, high temps, and many chemicals.

• When the endospore reaches a favorable environment, it can germinate back into a vegetative cell, which can then grow and reproduce.

• Medical significance: Since endospores are designed to survive outside of the host and are difficult to destroy, they can persist in the environment and potentially contribute to the spread of infection. Therefore, strict infection control is important in hospitals.

• Infection control: Because endospores are so resistant, hospitals must properly handle contaminated equipment and materials. Sterilization by Autoclaving is the most effective way to destroy endospores, while sporicides such as bleach can also be used.

3. A nurse documents that a patient presents with fever, sore throat, and swollen lymph nodes. Using the terms signs and symptoms, classify each of these findings and briefly explain the difference. (5 points)

Signs are objective findings that can be observed or measured by a healthcare professional.

• Fever → sign because it can be measured with a thermometer.

• Swollen lymph nodes → sign because they can be observed or felt during a physical examination.

Symptoms are subjective experiences that are reported by the patient and cannot be directly measured by someone else.

• Sore throat → symptom because the patient reports feeling pain or discomfort in their throat.

*Difference: Signs are objective and measurable/observable, while symptoms are subjective and experienced/reported by the patient.

4. Consider an outbreak of gastrointestinal illness in a nursing home. Identify the reservoir, source, and mode of transmission if the illness was spread by contaminated food. Suggest one nursing intervention that could reduce future cases. (4 points)

• Reservoir: An infected food handler/person can be the reservoir because a reservoir is the place where a pathogen normally lives and multiplies. In this case, the pathogen could be living in an infected person and then be transferred to the food.

• Source: The contaminated food is the source because the source is the person, animal, or substance from which the pathogen is acquired. The residents acquire the pathogen directly from eating the contaminated food.

• Mode of transmission: Vehicle transmission occurs because the contaminated food acts as an inanimate vehicle that carries the pathogen to the residents, who become infected when they eat it.

• Nursing intervention: Require food handlers to wash their hands thoroughly with soap and water after using the bathroom and before preparing or serving food, and exclude sick food handlers from preparing food. These measures can help prevent contamination of food and reduce the chance of future cases.

5. Gram-positive and Gram-negative bacteria respond differently to antibiotics. Compare the cell wall structures of these two groups and explain why Gram-negative bacteria are often harder to treat. (6 points)

• Gram-positive bacteria have a thick peptidoglycan (PG) layer and lack an outer membrane. The thick peptidoglycan layer helps them resist drying and mechanical stress. However, because their peptidoglycan layer is exposed, they are generally more sensitive to antibiotics that target peptidoglycan.

• Gram-negative bacteria have a thin peptidoglycan layer and an additional outer membrane containing lipopolysaccharide (LPS). The outer membrane acts as a selective barrier that can protect the cell from certain antibiotics, drugs, lysozyme, detergents, and disinfectants.

• Gram-negative bacteria are often harder to treat because their outer membrane provides an additional barrier that can prevent or limit certain antibiotics from reaching their targets inside the cell. This makes Gram-negative bacteria more resistant to some antimicrobial agents than Gram-positive bacteria.

• The difference in their cell walls also explains their Gram stain results: Gram-positive bacteria retain the crystal violet stain and appear purple, while Gram-negative bacteria have a thin peptidoglycan layer and outer membrane, lose the crystal violet during the alcohol step, and take up the counterstain, appearing pink/red.

6. Yeasts and molds are both fungi. Compare them by describing one structural difference and one clinical scenario where each might cause disease in humans. (4 points)

• Structural difference: Yeasts are unicellular, while molds are multicellular. Their colonies also look different: yeast colonies are usually smooth and creamy, while mold colonies are typically fluffy.

• Yeast clinical scenario: After taking antibiotics, a patient develops a vaginal yeast infection caused by Candida. The antibiotics can disrupt the normal microbiota, allowing Candida to overgrow and cause infection.

• Mold clinical scenario: A person develops ringworm, a fungal infection of the skin caused by a dermatophyte. The fungus can grow on the skin and cause infection, especially when it has access to the keratin in the outer layers of the skin.

7. A nursing unit is experiencing a norovirus outbreak. State whether norovirus is enveloped or naked and explain why this matters for cleaning protocols. Identify the category of transmission precautions that should be implemented. (4 points)

• Norovirus is a naked (non-enveloped) virus because it does not have a lipid envelope surrounding its capsid. Enveloped viruses have a lipid layer that is acquired from the host cell membrane during viral budding.

• This matters for cleaning because norovirus is not as susceptible to alcohol disinfection. Since it does not have the lipid envelope that alcohol can disrupt, alcohol-based disinfectants are less effective against it. Therefore, cleaning methods such as using bleach to disinfect contaminated surfaces can be used to help eliminate the virus.

• Transmission precautions: Contact Precautions should be implemented because norovirus can spread through direct and indirect contact with infected people or contaminated surfaces and objects. Healthcare workers should use gloves and gowns, and single-use equipment should be used when possible to prevent contaminated equipment from being used with another patient.

• Hand hygiene: Careful handwashing with soap and water is important during a norovirus outbreak because alcohol-based hand sanitizers are not as effective against naked viruses.

8.  You are educating new nurses about exotoxins vs. endotoxins. Create a comparison table to describe the differences. (8 points)

Exotoxins	Endotoxins
Proteins produced and secreted by bacteria	Lipopolysaccharides (LPS) that are an integral part of the outer membrane of Gram-negative bacteria
Can destroy host cells or inhibit metabolic functions and are usually highly specific for their targets; some are highly lethal even in small doses	The Lipid A portion of LPS is responsible for the toxic effects and triggers an inflammatory response
Can be released by living bacteria as they produce and secrete the toxin	Released when the outer membrane is disrupted, such as when the bacterial cell dies
Antitoxins are antibodies that can provide immunity against specific exotoxins. Toxoids are inactivated exotoxins used in vaccines	Can cause an excessive inflammatory response leading to endotoxic/septic shock, low blood pressure, multi-organ failure, and potentially death
Can be named for the organism that produces them or the cell type they target	Found only in Gram-negative bacteria because only Gram-negative bacteria have an outer membrane containing LPS

9. A patient with HIV develops oral thrush caused by Candida albicans. Explain how this infection demonstrates the concept of an opportunistic pathogen and dysbiosis. (5 points)

• Normal microbiota are microorganisms that normally live in and on areas of the body exposed to the outside environment, such as the skin, respiratory tract, mouth, and digestive tract. Candida albicans can normally be part of the microbiota of the mouth without causing disease.

• Candida albicans is an opportunistic pathogen because it can normally be part of the microbiota but can cause disease when the host is weakened, or when it enters a different or inappropriate body site.

• In a patient with HIV, HIV specifically attaches to and infects CD4 (helper) T cells, weakening the immune system. This allows C. albicans already present in the mouth to overgrow and cause oral thrush.

• This demonstrates dysbiosis, which occurs when the normal balance of microbiota is disrupted. The weakened immune system allows Candida to increase and become harmful rather than remaining a normal part of the microbiota.

• Therefore, this infection demonstrates that normal microbiota can become opportunistic pathogens when conditions change, especially when the host's immune defenses are weakened.

10. List the main criteria used to classify viruses; describe those structures. (4 points)

• Viruses are classified into families rather than using the normal binomial nomenclature system because viruses are acellular (not made of cells) and are not considered living organisms. Virus family names are italicized, begin with a capital letter, and end in -viridae, such as Herpesviridae.

• Type of nucleic acid: Viruses are classified as having DNA or RNA, which is the most important criterion.

• Envelope: Viruses can be enveloped, meaning they have a lipid envelope surrounding the capsid, or naked/non-enveloped, meaning they lack an envelope.

• Genome arrangement: The genome can be single-stranded or double-stranded, linear or circular, and segmented or non-segmented.

• Capsid shape: Viruses are also classified by the shape of their capsid, which is the protein coat surrounding the viral nucleic acid.

11. Compare/contrast the structure and replication of enveloped and naked animal viruses.(4 points)

Structure:

• Enveloped: Has a lipid envelope surrounding the capsid, which is acquired from the host cell membrane during budding. The envelope contains viral proteins/spike proteins.

• Naked: Has no lipid envelope; the capsid is the outer protein structure and contains capsid proteins/spike proteins.

1. Attachment: Both attach to specific receptors on the host cell surface.

• Enveloped: Viral envelope proteins or spike proteins attach to specific host cell receptors.

• Naked: Viral capsid proteins or spike proteins attach to specific host cell receptors.

2. Penetration: The virus enters the host cell.

• Enveloped: Enters by membrane fusion or receptor-mediated endocytosis.

• Naked: Enters mainly by receptor-mediated endocytosis.

3. Uncoating: The capsid is removed/disassembled, releasing the viral genome into the host cell.

4. Replication (synthesis): Both use the host cell’s machinery as a factory to replicate the viral genome and make viral proteins. In enveloped viruses, envelope proteins are made and transported to the host cell membrane.

5. Assembly: Newly made viral genomes and proteins are put together to form new virions.

• Enveloped: The envelope is acquired as the new virion buds through the host cell membrane.

• Naked: New virions assemble without an envelope.

6. Release:

• Enveloped: Usually exits by budding, taking part of the host cell membrane to form its envelope; this is often less damaging to the host cell.

• Naked: Usually exits by lysis, causing the host cell to burst and release virions.

12. Identify the laboratory methods used to identify each different type of microbe (bacteria, fungi, protozoa, helminths and viruses) in the lab. Give a brief description of each method. (Note: In patient sample is not a method). (10 points)

• Bacteria:

  • Microscopy: Observes bacterial shape, size, and arrangement; commonly uses Gram staining to help identify bacteria.

  • Traditional culture: Grows and isolates bacteria on media containing nutrients needed for growth. Media allows us to observe microbial growth and metabolism.

  • Immunological methods: Uses antibodies to detect the microbe, or detects antibodies in the patient’s blood produced in response to infection.

  • Molecular methods: Detects or amplifies the bacteria’s DNA/RNA, such as with PCR.

• Fungi:

  • Microscopy: Common; uses special fungal stains such as KOH to see microscopic features like spores (Conidia)

  • Traditional culture: Grows fungi on media containing nutrients needed for fungal growth, allowing growth and metabolism to be observed.

  • Immunological methods: Rare; uses antibodies to detect the fungus or detects antibodies in the patient’s blood.

  • Molecular methods: Rare; detects fungal genetic material, such as with PCR.

• Protozoa (protists):

  • Microscopy: Common; uses special stains such as trichrome.

  • Traditional culture: Generally not used because they are too complicated to grow on plates.

  • Immunological methods: Extremely rare.

  • Molecular methods: Extremely rare.

• Helminths:

  • Microscopy: Common; identifies eggs, usually using special stains.

  • Gross examination: Identifies adult worms by their physical characteristics.

  • Traditional culture, immunological, and molecular methods: Generally not used or extremely rare.

• Viruses:

  • Microscopy: Not used because viruses cannot be seen with a normal light microscope.

  • Cell culture: Grow viruses in mammalian cell culture and identifies them by their characteristic cytopathic effects (CPE, visible effects on the cell).

  • Immunological methods: Common; uses antibodies to detect viral antigens, or detects antibodies in the patient’s blood against the virus.

  • Molecular methods: Very common; detects or amplifies viral DNA/RNA, such as with PCR/NAAT.

13. Name the four main categories of transmission precautions and explain what each entails. (4 points)

• Standard Precautions: Used for all patients. Includes hand hygiene, appropriate PPE, respiratory hygiene, safe injections, and proper handling of contaminated equipment and materials.

• Contact Precautions: Used for infections spread by direct or indirect contact. Healthcare workers wear gloves and gowns and use dedicated or single-use equipment when possible.

• Droplet Precautions: Used for infections spread through respiratory droplets, generally traveling short distances. Healthcare workers wear a surgical mask and use appropriate PPE.

• Airborne Precautions: Used for infections spread through small airborne particles that can remain suspended in the air and travel longer distances. Requires a respirator such as an N95 and appropriate airborne infection isolation measures.

14. Identify various bacterial flagella arrangements, and discuss how periplasmic flagella differ from regular bacterial flagella. (5 points)

• Monotrichous: One flagellum at one end of the bacterial cell.

• Lophotrichous: Multiple flagella at one end of the cell.

• Amphitrichous: Flagella at both ends of the cell.

• Peritrichous: Flagella distributed over the entire surface of the cell.

• Periplasmic flagella: Found in spirochetes, which are thin, spiral-shaped bacteria. The flagella are located in the periplasmic space between the inner and outer membranes and wrap around the cell. Their rotation produces a corkscrew-like movement and contributes to maintaining the spirochete’s spiral shape. Unlike regular flagella, they do not extend outward from the cell.

15. Describe features of each biosafety level (BSL). (8 points) a. Generally, which types of pathogens are placed in each level. (4 points) b. Describe minimum PPE required for each level. (4 points)

BSL-1

1. Key features:

• Hand-washing sinks must be available

• Work may be done on open lab bench

• No food, beverages, or chewing gum in the lab

2. Pathogens: Low-risk organisms that generally do not cause disease in healthy people. Example: E. coli K-12.

3. PPE: None specifically required.

BSL-2

1. Key features: Limited lab access,

• Most agents worked on at open lab bench spaces

• Biological safety cabinet needed when working with certain BSL-2 agents or samples, like tissues or bodily fluids, that may contain such agents

• Biohazard signage (signs indicating biosafety level, agents used, emergency contact personnel, etc.)

• Eye-wash stations must be present

• Lab design should allow easy cleaning and decontamination (no carpets, upholstery, etc.)

• Autoclave (a specialized machine for sterilizing)

2. Pathogens: Moderate-risk pathogens that are known to cause human disease but mostly cause infections that are preventable by vaccines, or at least treatable: hepatitis C virus, Salmonella, rabies virus, Zika virus, and HIV. BSL-2+ agents require additional precautions. Example: HIV.

3. PPE: Lab coat and gloves; safety glasses or a face shield if there is a splash risk.

BSL-3

1. Key features: Controlled/authorized access,

• Agents manipulated in biological safety cabinet

• People entering area warned of risks, vaccinated (if possible), and monitored for infection

• Decontaminate all waste + lab wear before laundering

• Special airflow management

• Self closing, double door access

2. Pathogens: Cause serious or lethal human diseases. Some of these agents have airborne transmission. Certain pathogens in this class are treatable, but because of the severity of disease, they are classified at a higher level. Example: Mycobacterium tuberculosis.

3. PPE:

• Protective lab covering

• Gloves

• Respirators if indicated

• Must wear PPE at all times

• PPE worn for BSL-3 work should not be worn in other areas

• Monitoring to ensure the worker has not been infected

BSL-4

1. Key feature: All BSL-1, -2, and -3 measures, plus:

• Specialized facility design and engineering

• Highly restricted/lockdown access

2. Pathogens: dangerous and so-called exotic pathogens that tend to be lethal in humans and do not have cures or treatments. Example: Ebola virus.

3. PPE: Airtight, pressurized full-body hazardous-material suit with air supplied through a specialized system; workers change clothing and shower before entering and leaving.

Viruses from the Required Video

• Lambda (λ) phage: a bacteriophage that infects E. coli. It can enter a lysogenic state, where its DNA becomes integrated into the bacterial genome as a prophage. It is an example of a phage that can affect bacterial populations.

• CTXφ: a bacteriophage associated with Vibrio cholerae. It carries genes for cholera toxin, so infection with CTXφ can give V. cholerae the ability to produce the toxin. This demonstrates how phages can transfer genes that increase bacterial virulence.

• φSa3ms: a bacteriophage associated with Staphylococcus aureus. It can carry virulence genes, including toxin-related genes, changing the characteristics of its bacterial host.

• Big idea from the video: bacteriophages can influence bacterial populations and can transfer genes that change how harmful bacteria are.

3.4 Define the term pleomorphic, and discuss how this property may impact an organism’s ability to cause infection

• Pleomorphic: Describes an organism that can change its shape or appearance.

• Pleomorphic bacteria may take on different shapes depending on their environment or growth conditions.

• This flexibility can help some bacteria adapt to different conditions within the host, potentially making it easier for them to survive and cause infection.

3.9 Name two acid-fast genera, state what makes them so, and explain why the acid-fast stain is clinically useful.

• Two acid-fast genera are Mycobacterium and Nocardia.

• They are acid-fast because their cell walls contain a high concentration of mycolic acids, which are waxy lipids.

• These waxy lipids make the cells resistant to decolorization by acid-alcohol.

• The acid-fast stain is clinically useful because it helps identify bacteria with these unusual cell walls, including pathogens that can cause tuberculosis and other infections.

4.6 Name and describe the two main groups of parasitic helminths.

• Nematodes (roundworms): round, non-segmented worms with a complete digestive tract.

• Platyhelminths (flatworms): flattened worms that include:

  • Cestodes (tapeworms): long, flat, segmented worms.

  • Trematodes (flukes): flat, non-segmented worms.

4.7 Explain what fungal hyphae are, and name the two forms of hyphae.

• Hyphae are long, threadlike structures that make up the body of many fungi.

• A mass of hyphae is called a mycelium.

• Septate hyphae: divided by cross-walls called septa.

• Aseptate (coenocytic) hyphae: lack septa, so the cytoplasm is continuous.

4.10 Explain why Protista is sometimes described as a catch-all kingdom.

• Protista is sometimes called a catchall kingdom because it contains diverse eukaryotic organisms that do not fit well into the plant, animal, or fungal kingdoms.

• Protists can be unicellular or multicellular, and they have very different structures and ways of obtaining nutrients.

• Not a true family tree: Because genetic research shows many protists are not closely related to one another, scientists often compare the kingdom to a biological "junk drawer

4.15 Discuss the basic structure of eukaryotic flagella, and compare eukaryotic and prokaryotic flagella.

• Eukaryotic flagella are long, flexible structures made of microtubules arranged in a 9 + 2 pattern and covered by the plasma membrane.

• They move with a whiplike motion.

• Prokaryotic flagella are made of flagellin, are not membrane-covered, and rotate like a propeller.

• Eukaryotic flagella are structurally more complex and are related to the eukaryotic cytoskeleton.

4.18 Explain the structure and function of the cytoskeleton, and name the organelle that builds microtubules.

• The cytoskeleton is a network of protein fibers that provides cell shape, support, organization, and movement, complex cell transport.

• It consists of:

  • Microfilaments: thin fibers made mainly of actin.

  • Intermediate filaments: provide strength and stability.

  • Microtubules: hollow tubes made of tubulin; help with movement and transport within the cell.

• The centrosome organizes and builds microtubules.

ER, Golgi, and mitochondria endosymbiotic

4.20 Discuss the basic structural and functional features of the endoplasmic reticulum.

• The endoplasmic reticulum (ER) is a network of interconnected membranes inside the cell.

• Rough ER: has ribosomes attached; makes and begins processing proteins that will be secreted, inserted into membranes, or sent to certain organelles.

• Smooth ER: lacks ribosomes; involved in lipid production, detoxification, and calcium storage.

4.21 Describe the general structural and functional features of the Golgi apparatus.

• The Golgi apparatus consists of flattened membrane sacs called cisternae.

• It modifies, sorts, and packages proteins and lipids received from the ER.

• It sends these materials to their proper destinations in vesicles.

• It also helps produce lysosomes.

Mitochondria are similar to bacteria because they have:

• Their own, Circular DNA

• 70S-like ribosomes

• A double membrane

• The ability to divide independently

6.6 Describe the key contributors to and consequences of viral genome evolution, and state why RNA viruses evolve faster than DNA viruses.

• Viral genomes evolve through mutation, recombination, and reassortment.

• Mutation: changes in the nucleotide sequence.

• Recombination: genetic material from different viruses can be combined.

• Reassortment: occurs when viruses with segmented genomes exchange entire genome segments.

• Genome evolution can change virulence, host range, immune recognition, and susceptibility to antiviral drugs.

• RNA viruses generally evolve faster because their RNA-dependent polymerases usually lack the proofreading ability of DNA polymerases, so replication produces more mutations.

6.7 Compare and contrast antigenic shift and antigenic drift, and state how they impact influenza virus evolution and outbreaks

• Antigenic drift: gradual accumulation of small mutations in influenza virus genes, causing small changes in viral surface antigens.

  • Occurs frequently and contributes to seasonal influenza outbreaks.

• Antigenic shift: sudden, major change caused by reassortment of genome segments when different influenza viruses infect the same cell.

  • Can create a novel influenza strain that many people have little immunity to, potentially leading to a pandemic.

6.11 Summarize the conventions for naming viruses.

• Virus names commonly describe characteristics such as the disease caused, location, host, structure, or scientist associated with the virus.

• Virus species names are assigned according to conventions established by the International Committee on Taxonomy of Viruses (ICTV).

• Virus names and the names of the diseases they cause are not always the same.

6.17 Explain what makes a virus oncogenic, and name examples of oncogenic viruses and the cancers they may cause.

• An oncogenic virus can contribute to cancer by altering normal cell growth and division.

• Viral genes or viral effects on host genes can cause uncontrolled cell division or interfere with tumor-suppressor mechanisms.

• Examples:

  • Human papillomavirus (HPV): cervical cancer and several other cancers.

  • Epstein-Barr virus (EBV): some lymphomas and nasopharyngeal cancer.

  • Hepatitis B virus (HBV): hepatocellular (liver) carcinoma.

  • Hepatitis C virus (HCV): hepatocellular carcinoma.

  • Human T-cell leukemia virus type 1 (HTLV-1): adult T-cell leukemia/lymphoma.

6.20 Describe several methods for detecting viral proteins and genetic material, and state their advantages and limitations.

• ELISA: detects viral antigens or antibodies using specific binding reactions.

  • Advantage: relatively quick and useful for large numbers of samples.

  • Limitation: may be less sensitive than molecular methods and can sometimes produce false results.

• PCR/RT-PCR: detects viral DNA or RNA by amplifying genetic material.

  • Advantage: highly sensitive and specific; can detect very small amounts of viral genetic material.

  • Limitation: detecting viral genetic material does not always mean the virus is currently infectious.

• Nucleic acid hybridization: uses complementary nucleic acid probes to detect specific viral sequences.

  • Advantage: specific for the targeted genetic sequence.

  • Limitation: generally less sensitive than PCR.

• Immunofluorescence: uses fluorescent antibodies to detect viral proteins in cells.

  • Advantage: can show which cells contain viral antigens.

  • Limitation: requires specific antibodies and specialized equipment.

6.21 Explain the different drug approaches to managing viral infections, and name several antiviral drugs.

• Antiviral drugs target specific stages of the viral life cycle, such as:

  • Viral attachment or entry.

  • Genome replication.

  • Viral protein processing.

  • Assembly or release.

• Because viruses use host-cell machinery, antiviral drugs can be difficult to design without also affecting the host.

• Examples:

  • Acyclovir: used against herpesviruses; interferes with viral DNA replication.

  • Oseltamivir (Tamiflu): inhibits influenza virus release.

  • Remdesivir: inhibits viral RNA replication and is used for certain viral infections.

  • Nirmatrelvir/ritonavir (Paxlovid): inhibits SARS-CoV-2 viral protein processing.

• Antiviral treatment generally works best when the virus is actively replicating, and different drugs work against specific viruses. Used to treat symptoms but can’t “kill” viruses because they’re not living

10.5 Define pathogenicity and virulence.

• Pathogenicity is the ability of a microorganism to cause disease.

• Virulence is the degree or severity of disease caused by a pathogen.

• Therefore, pathogenicity describes whether a microorganism can cause disease, while virulence describes how severe the disease is.

10.8 Explain why virulence is best viewed as an evolving property.

• Virulence is an evolving property because pathogens can mutate and adapt to changes in their hosts and environments.

• Natural selection favors traits that help pathogens survive and reproduce.

• Changes in host immunity, treatments, or transmission conditions can therefore cause virulence to increase or decrease over time.

10.9 Define the term attenuated pathogen.

• An attenuated pathogen is a pathogen that has been weakened so that it has a reduced ability to cause disease. Loss of virulence factors

• It can still stimulate an immune response and is therefore used in some live attenuated vaccines.

10.13 Identify the five tasks a pathogen must complete to successfully infect a host.

• Enter the host – The pathogen utilizes a specific portal of entry (such as mucous membranes or broken skin) to gain access into the body.

• Adhere to host tissues – Once inside, the pathogen must attach itself to host cells or surfaces to avoid being washed away by bodily fluids.

• Invade tissues and obtain nutrients – The pathogen penetrates deeper into tissues and acquires critical resources (such as iron) to survive and multiply.

• Replicate while evading immune defenses – The microbe must replicate successfully while actively warding off or hiding from the host’s immune system cells.

10.14 Identify various portals of entry and exit.

• Portals of entry are locations where pathogens enter the body:

  • Respiratory tract: nose and mouth.

  • Gastrointestinal tract: mouth.

  • Genitourinary tract: urinary and reproductive openings.

  • Skin: usually through cuts, wounds, bites, or punctures.

  • Parenteral route: direct entry through breaks in the skin or mucous membranes.

• Portals of exit are routes pathogens use to leave the body:

  • Respiratory secretions: coughing and sneezing.

  • Feces: gastrointestinal infections.

  • Urine: urinary infections.

  • Blood: bloodborne infections.

  • Skin lesions or wound drainage.

  • Genital secretions.

10.18 Explain the relationship between symptoms and mode of transmission.

• Symptoms can affect the mode of transmission by helping pathogens leave the host and reach another host.

• Coughing and sneezing release respiratory pathogens and promote respiratory transmission.

• Vomiting and diarrhea release gastrointestinal pathogens and can promote fecal-oral transmission.

• Therefore, symptoms that help a pathogen reach its portal of exit can increase its ability to be transmitted.

10.20 Identify the basic criteria for assigning pathogens to a biosafety level.

• Level of infectivity (not necessarily level of contagiousness)

• Extent of disease caused and mortality rates

• Mode of transmission

• Availability of preventive measures and treatments for the disease