Micro Exam #4

Discuss the origin, structure, and function of the viral envelope

• The envelope is acquired from the host cell during viral replication.

• Comprised of a phospholipid bilayer.

• Some of the proteins on the envelope are from the virus.

• The envelope does not act like a cell membrane.

• Enveloped viruses are easier to kill than non-enveloped

List the characteristics by which viruses are classified

• Type of Nucleic Acid

• Presence of an Envelope

• Shape

• Size

Sketch and describe the five stages of the lytic replication cycle as it typically occurs in bacteriophages

1. attachment

2. entry

3. synthesis

4. assembly

5. release

Compare and contrast the lysogenic replication cycle of viruses with the lytic cycle

Explain the differences between bacteriophage replication and animal viral replication

take note of the glycoprotein spike on the envelope of the animal virus.

attachment of lytic cycle

Virions are nonmotile so contact with host cell is random.

▪ Dependent upon chemical attraction and precise fit between tail fibers and host receptors.

▪ In the case of the E coli phage, it will only attach to pili, cell walls or flagella of that specific type

entry of lytic cycle

To break through cell wall, the phage will release lysozyme to dissolve through cell wall.

▪ The tail sheath of the virus then contracts and forces a tube into the bacterial cell.

▪ After entry, viral enzymes degrade the bacterial DNA into its constituent nucleotides

synthesis of lytic cycle

After the bacterial chromosomes are degrades it stops making its own molecules and begins

synthesizing new viruses directed by the viral genome.

▪ For dsDNA viruses, the viral genome directs the synthesis of new capsid proteins, tail, viral

polymerase and lysozyme

assembly of lytic cycle

Capsid proteins begin to assemble inside the host cell.

▪ Tails and tail fibers begin to assemble and attach to head.

▪ Capsids form around viral genomes or the genomes are pumped into the newly formed capsid.

release of lytic cycle

• As lysozymes weakens the cell wall of the bacterium the new virions can burst free from the cell.

• For the T4 bacteriophage the whole process takes about 25 minutes and up to 200 new virions are released.

▪ Burst time – how long it takes to complete the process.

▪ Burst size – how many new virions are released

attachment of lysogenic cycle

Same as in lytic cycle, but the host cell’s DNA is not destroyed

attachment of entry cycle

viral DNA remains silent as a prophage

prophage entry of lysogenic cycle

Prophage incorporates itself in the host cell’s DNA

lysogeny of lysogenic cycle

• Every time the bacterial chromosome replicates, the viral DNA is copied along with it.

• All daughter cells will now carry the prophage.

• Lysogenic phages can cause the phenotype of the bacterium to change from harmless into pathogenic

induction of lysogenic cycle

• At some point the prophage may be excised from the host DNA.

• At this point it reenters the lytic phase

• Inductive agents include: physical and chemical agents that damage bacterial DNA

Compare and contrast the replication and synthesis of DNA, -RNA, and +RNA viruses

Compare and contrast the release of viral particles by lysis and budding

Lysis: (Explosive Exit) Viruses build up inside the cell until it ruptures. The host cell is killed. This is typical for bacteriophages and non-enveloped animal viruses.

Budding:(Stealthy Exit) Virus pushes out of the membrane, taking a portion of it as its envelope. The host cell often survives for a time, allowing prolonged viral production. Common in enveloped viruses like HIV, Influenza, and Herpes.

Compare and contrast latency in animal viruses with phage lysogeny

Lysogenic phages can cause the phenotype of the bacterium to change from harmless into pathogenic, integrates into a bacterial chromosome. Phage lysogeny occurs when a bacteriophage (a virus that infects bacteria) enters a dormant state inside a bacterial cell instead of immediately replicating and lysing the host.

Latency in animal viruses occurs when a virus enters a host cell and establishes a long-term, dormant infection without producing new virus particles right away.

There are three methods for viruses to enter animal cells

1. Direct Penetration – done by some naked viruses.

2. Membrane fusion – phospholipid of the viral envelope fused with host cell.

3. Endocytosis – when the virus trigger receptors on the cell surface to engulf the entire virion

Explain in simple terms how a cell may become cancerous, with special reference to the role of viruses.

Two-hit viruses cause cancer.

The most well-known is cervical cancer caused by HPV (solve by HPV vaccine)

In the Two Hit hypothesis, a virus inserts a promotor that converts a protooncogene into an oncogene. Often this first hit doesn’t cause cancer, but if a second hit damages the downstream repressor gene, then the oncogene disrupts cell division and causes cancer

Protooncogenes

are genes in a host cell involved in normal cell division.

Describe some ethical and practical difficulties to overcome in culturing viruses

ethical difficulties: use of living host (this raises concerns about chicken eggs used to work on vaccines). Informed consent. Risk of biohazard exposure. Genetic modification.

physical difficulties: viruses can’t grow on their own. Host specificity. Slow growth and detection. Contamination risks.

Explain the use of a plaque assay in culturing viruses in bacteria

Quantification: Provides an accurate count of infectious phages.

Purification: Individual plaques can be picked to isolate pure phage clones.

Visual Confirmation: Easy to see and measure viral activity.

Efficiency: Helps assess host range, mutation rates, or lytic ability of a phage.

Discuss aspects of viral replication that are lifelike and non-lifelike.

lifelike: reproduction (with help), genetic material (contain DNA and RNA), adaptation, high specificity

non-lifelike: no metabolism, incapable of independent replication, no cellular structure, do not grow

Define and describe prions

These are infectious protein particles, not viruses.

Prion replication process

• In human prion diseases a normal PrP protein’s structure becomes altered and begins to affect other

PrP proteins around it.

• As more of the altered PrP proteins aggregate it causes neurons to die and leave holes in the brain.

• Diseases caused by prions are called spongiform encephalopathies

Prions are different from viruses because:

1. no genetic material, just proteins

2. simpler structure

3. Prions replicate by converting normal proteins into the misfolded prion form—no need for genes or host-cell machinery.

Describe methods to control and destroy prions

They are not removed through normal autoclaving or decontamination processes.

1. excess heat

2. autoclaving with special conditions

3. chemical decontamination

List four diseases caused by prions.

BSE – Mad Cow disease (most famous)

CWD – in deer and elk (most common the US)

vCJD – in humans (100% fatal)

Kuru - earlier discovered in a tribe

Scrapie - in sheep and goats

Distinguish among four types of symbiosis

1. Mutualism

2. Commensalism

3. Amensalism

4. Parasitism

Describe the relationships among terms parasite, host, and pathogen

1. A parasite is an organism that lives on or in another organism (the host) and benefits at the host’s expense

2. The host is the organism that the parasite lives in or on.

3. A pathogen is any disease-causing agent. It includes parasites, but also bacteria, viruses, fungi, and prions. So: All parasites that cause disease are pathogens, but not all pathogens are parasites.

Describe the relationships among terms parasite, host, and pathogen simply:

A parasite lives in/on a host.

If the parasite causes disease, it is also considered a pathogen.

A host is negatively affected by the presence of a parasite or pathogen.

Describe the microbiome, including resident and transient members.

The microbiome refers to the community of microorganisms—including bacteria, viruses, fungi, and protozoa—that live in and on the human body

Residents are to be expected. Transients are temporary visitors and eliminated by the immune system.

Resident microbiota

Upper respiratory tract - strep or staph

Upper digestive tract (oral cavity) - strep, Neisseria, staph, treponema

Lower Digestive tract

Female Genitourinary tract - corynebacterium, lactobacillus

Male Genitourinary tract - corynebacterium, streptococcus

Eyes and Skin - candida albacans, gram + organisms

Transient microbiota

• Temporary hitchhikers for hours, days, etc.

• Found in the same places as resident until they are dislodged by competition, immune cells, or changes to the host body

• Rid through the immune system

• Examples: Skin bacteria you pick up from a doorknob. Bacteria in food that pass through the gut without colonizing

Describe three conditions that create opportunities for normal microbiota to cause disease.

1. immune system weakened

2. antibiotics. changes in normal flora

3. introduction to a new site in the body

4. stressful conditions

Describe three types of reservoirs of infection in humans

A reservoir of infection is any place where a pathogen normally lives, grows, and multiplies—basically, where it “hangs out” before infecting someone

1. animals (zoonoses)

2. human carriers (sneezing, coughing, physical touch). Typhoid mary.

3. nonliving reservoirs: soil (anaerobes like clostridium), water, food

Describe the relationship between contamination and infection

Contamination: the presence of microbes on or in the host’s body. Can have no effect. They can become part of our normal flora. Remain as transients for a time. Become pathogens

Infection: When a microbe invades one of our normal systems and overwhelms it. Some infections do not cause disease.

Identify and describe the portals through which pathogens invade the body

skin

mucous membrane (major portal of entry). most common portal is the respiratory membrane

placenta

the parenteral role

List the types of adhesion factors and the roles they play in infection

1. Viruses and bacteria most commonly use lipoprotein or glycoprotein ligands that allow them to attach to receptors on the host cells

2. Fimbriae and Pilli will stick to the host cell’s surface

3. Biofilms: The sticky web created when certain pathogens interact with each other inside the host. Remember that many organisms only cause disease when they are in biofilm form. Some bacteria will change their phenotype drastically when in a biofilm

Explain how a biofilm may facilitate contamination and infection

1. Microbes land on a surface

2. Biofilm forms and protects the colony

3. Surface becomes contaminated

4. Microbes break off and infect new areas

5. Infection becomes chronic and hard to treat

define infection

When a pathogen invades a host

define disease

When the injury caused by the pathogen is significant enough to interfere with normal functioning

of the host

define morbidity

Refers to the state of being diseased or the rate of disease in a population. Measures how many people get sick (not necessarily die).

define pathogenicity

The ability of a microorganism to cause disease. It’s a yes/no property—can it cause disease or not?

define virulence

The degree or severity of pathogenicity. In other words, how harmful or aggressive the pathogen is once it causes disease.

Symptoms

Symptoms – Subjective characteristics sensed by the patient.

▪ Pain

▪ Nausea

▪ Headache

▪ Sore throat

▪ Fatigue

▪ Itching, cramps etc.

Signs

Signs – Objective signs of disease that are measurable.

▪ Swelling

▪ Rash or redness

▪ Vomiting

▪ Diarrhea

▪ Fever

▪ Increase or decrease in WBC’s

▪ Increase or decrease in HR

▪ Increase or decrease in BP

Syndrome

Syndrome – A group of signs and symptoms that characterize a disease.

▪ AIDS – hallmarks are malaise, decrease in T4 cells, diarrhea, weight loss, pneumonia, other rare

fungal infections and cancers

Explain how microbial extracellular enzymes affect virulence

Extracellular Enzymes

▪ Hyaluronidase – destroys hyaluronic acid a key substance in ground substance.

▪ Collagenase – destroys collagen allowing bacteria to spread.

▪ Coagulase – causes blood clotting (what lab test did we do for this?)

▪ Kinases (Streptokinase, Staphylokinase) – digest blood clots and release bacteria

Explain how microbial extracellular toxins affect virulence

Exotoxins – produced and released by the bacteria.

▪ Cytotoxins

▪ Neurotoxins

▪ Enterotoxins

▪ Endotoxins – The lipid A component of a gram negative cell wall

▪ Released when the cells die or are destroyed by the host.

▪ Can cause – fever, inflammation, diarrhea, hemorrhage, shock, coagulation

Explain how microbial extracellular adhesion factors affect virulence

These include fimbriae, pili, surface proteins, and viral spikes that help pathogens attach to host cells.

🔹 How they increase virulence:

Allow microbes to stick to host tissues, resist flushing mechanisms (like mucus or urine), and colonize specific areas.

Explain how microbial antiphagocytic factors affect virulence

• Capsules – are composed of the same things as body cells. Can evade detection for longer. Some capsules also make the bacteria very slippery and had to grab.

• Antiphagocytic Chemicals – chemicals produced by bacteria that prevent lysosomes in the phagocytes from attaching to the bacteria and allows them to survive inside the phagocytes. E.g. – M factor produced by Strep pyogenes

List and describe the five typical stages of infectious diseases

1. incubation period

2. prodromal period

3. illness

4. decline

5. convalescence

incubation period

• Time between infection and when symptoms first appear.

• Depends upon the virulence of the microbe, the infective dose, state of the health of the host, nature of the pathogen, and the site of infection.

• Even the same pathogen will have different incubation periods based upon the factors above

prodromal period

• A short period of generalized mild signs and symptoms.

• Some infectious diseases skip this step. (think about GI bugs)

illness

• Most severe stage, signs and symptoms are in full bloom.

• Host’s immune system has not responded adequately yet or is being overwhelmed.

• This is often, but not always the most infective stage for the patient as well

decline

• This is when the patient’s immune system or the effect of medications helps get rid of the

pathogen.

• Fever and other signs go away.

• Can still be quite sick from the aftereffects.

convalescence

• Tissues are repaired and body function returns to normal.

• Length depends upon the most of the same factors as in the incubation stage.

• Note: You can be infective in every stage listed above. For some diseases you can even continue to be infective after you have recovered.

Contact transmission

contains direct contact, indirect contact, and droplet transmission

Vehicle transmissions

contains airborne, waterborne, foodborne, and bodily fluids

Vector transmission

contains biological vectors and mechanical vectors

direct contact

▪ Involves bodily contact between individuals

▪ Touching, kissing, sexual intercourse between humans

▪ Biting, scratching in zoonoses.

▪ Vertical transmission of disease via the placenta.

▪ Self-transmission – please look at the book

indirect contact

▪ Fomites – inanimate objects that transfer pathogens.

▪ E.g. – toothbrushes, toys, money, diapers, stethoscopes, contaminated needles, etc

droplet

▪ Droplets of mucus propelled out of the body by breathing, coughing, sneezing.

▪ This is for larger droplets that travel 1m or less.

airborne

Spread of droplets further than 1 m away.

▪ Aerosols – tiny droplets that can travel much further.

▪ Common ones – dental and surgical drills, improper flaming of loops in lab

waterborne

Water can act as a reservoir of infection as well as a vehicle.

▪ Fecal-oral route – any fecal contamination of food or utensils

foodborne

Pathogens on foods that are improperly stored, undercooked or improperly handled.

▪ It is usually another route of fecal-oral contamination

bodily fluids

Often considered under waterborne, but also can be direct contact.

▪ Blood, urine, feces, vaginal and seminal secretions.

▪ Should always be treated as if they contain pathogens

biological vectors

Usually caused by the bite of an arthropod vector (ticks, lice, mosquitos)

▪ Biological vectors often serve as important intermediate hosts for the life stages of certain

pathogens as well

mechanical vectors

Passively carry pathogens to new hosts on their feet or other body parts.

▪ Common examples include houseflies and cockroaches

Define epidemiology

The study of Where and When disease occurs and How it spreads through a population.

▪ Where – Place

▪ When – Time

▪ How – Person (who is affected, what are the reservoirs, modes of transmission)

Contrast incidence and prevalence

incidence: The number of new cases in a population in a given time period

prevalence: The total number of cases in a population in a given time period.

endemic

Disease found regularly in the population

sporadic

when only a few cases are found

epidemic

When there are more cases than statistically predicted or historically reported in a period.

▪ Observed versus expected cases

pandemic

An epidemic that spreads across multiple countries or continents, affecting a large portion of the global population.

endemic, sporadic, epidemic, and pandemic summarized

endemic, sporadic, epidemic, and pandemic

Explain three approaches epidemiologists use to study diseases in populations

1. Descriptive - Case studies, Case Reports

2. Analytical – Cross-sectional, Case-Control, Cohort

3. Experimental - Clinical Trials, Koch’s Postulates

Explain how healthcare-associated infections differ from other infections

Exogenous – picked up in a healthcare setting

Endogenous – opportunists because of treatment

Latrogenic – caused by things like catheters, surgery, wrong antibiotics

factors influencing: Presence of microbes in the hospital setting. Immunocompromised patients. Transmission of pathogens between staff, and patients

Describe the factors that influence the development of healthcare-associated infections

factors Influencing HAIs

▪ Presence of microbes in the hospital setting

▪ Immunocompromised patients

▪ Transmission of pathogens between staff, and patients

Describe three types of healthcare-associated infections and how they may be prevented.

Controlling HAIs

▪ All the things you can think of that would prevent spread.

▪ Ignatz Semmelweis was right!

▪ Handwashing protocols can reduce infection by more than 50%

specific immune response

Specific = Adaptive

▪ Every response is unique

▪ The second exposure to a pathogen garners a much faster response by the immune system

because it remembered the pathogen from previous encounters

non-specific immune response

Nonspecific = Innate

▪ Every response is the same

▪ IT HAS NO MEMORY

▪ Cannot differentiate between types of invasions, every pathogen is treated the same

what are the physical barriers of a non-specific immune response?

-Skin and mucous membranes, tears, coughing, sneezing etc.

▪ Acidic secretions from skin destroy pathogens.

▪ Stomach acid and enzymes kill microorganisms.

▪ Saliva and tears have lysozymes that destroy bacteria.

▪ Mucosa of the nose, throat etc. trap and expel pathogens.

▪ Overall function is to prevent entrance of pathogens into the body.

▪ Can be breached when the skin is broken

Chemical – how do these work, what are they effective against in non-specific immune responses?

• These help destroy or inhibit microbes

• target bacteria and viruses

• some chemical barriers:

  • acidic pH, lysozome, sebum, mucus, defensins

complement system

• non-specific immune response

• a group of about 20 proteins when exposed to bacterial antigens.

  • Classical pathway: stimulation by antigen-antibody complex

  • Alternate pathway: stimulation by microorganism’s cell wall. Stimulated by factors C3 which break down into different components

interferons

• non-specific immune response

• protects body against viral attack

• Virus infected cells produce interferon which stimulates neighboring cells to produce antiviral proteins

toll-like receptors (TLRs)

• non-specific immune response

• Trigger your body’s responses to a number of various bacterial and viral pathogens.

• There are 10 different TLR’s found on human phagocytes.

• Binding of Pathogen Associated Molecular Patterns (PAMP) triggers infected cells to do things like apoptosis, initiate the inflammatory mechanism, or stimulate the adaptive response

cells

• non-specific immune system (primarily WBCs)

• neutrophils, macrophages, basophils, mast cells, eosinophils, lymphocytes

Which type is first to enter the infected site?

Neutrophils are the first to arrive and are the most numerous WBCs in acute inflammation

Neutrophils

phagocytes – about 126 billion/day produced.

▪ Usually the first WBC to make it to an infection.

▪ 1 time use (like a honeybee stinger).

▪ Pus =dead neutrophils, microbes, pathogens

Macrophages

-monocytes in blood, macrophages in tissue.

▪ Leave blood and increase numbers at site of infection.

▪ They are the cleanup crew.

▪ Include many different types – dendritic cells, microglia, alveolar, hepatic

basophils

mobile

▪ Release factors which attract more WBC’s (chemotactic factors)

mast cells

nonmobile

▪ Are found near sites of possible pathogen influx

▪ Release chemotaxic factors

▪ Can also phagocytose bacteria

eosinophils

Act as moderators of inflammatory response and kill parasites by releasing enzymes all over them

Roles of Eosinophils and Basophils in Inflammation

eosinophils: Contribute to allergic reactions

basophils: Release histamine, which promotes vasodilation and increased permeability. Also contribute to allergic inflammation

vascular permeability

allows protein rich fluid to seep into the injured region from the blood vessels (called exudate)

(Blood vessels become leaky, allowing immune cells and proteins to exit into tissue. Helps deliver complement and antibodies.)

vasodilation

caused by the release of histamines, prostaglandins, etc. from the injured tissues. (Blood vessels widen (due to histamine, etc.). Increases blood flow, causing redness and heat.)

chemotaxis

• Chemical signals attract immune cells (especially neutrophils and monocytes).

• Gradient of cytokines/chemokines guides them to the site of infection.