Chapter 14 videos Flashcards
What is normal microbiota?
- Organisms that colonize the body’s surfaces without
normally causing disease - Also termed normal flora and indigenous microbiota
What are the two types of normal microbiota?
- Resident microbiota
* normal microbiota throughout life, mostly commensal
* They don’t normally caused harm to the person. - Transient microbiota
* Remain in the body for short period
* Found in the same regions as resident microbiota
* Cannot persist in the body
* Competition from other microorganisms
* Elimination by the body’s defense cells
* Chemical or physical changes in the body
When do you acquire normal microbiota?
- Fetus in womb is free of microorganisms
- Microbiota begin to develop during birthing process
- Much of one’s resident microbiota are established during first months of life
Define infectious diseases.
Infectious disease is an illness caused by a pathogen
Define Epidemiology.
Epidemiology is the monitoring and controlling of disease occurrence to promote public health.
What is a microbe?
Organisms too small to be seen without a microscope
What is a pathogen?
A microorganism capable of causing disease.
Six groups viruses, prions, bacteria, protozoans, helminths, and fungi
What is pathogenicity?
Microbes ability to cause disease
What is virulence
A measure of pathogenicity
What are two types of pathogen?
True or (primary pathogens)
* Can cause disease in a host regardless of the host’s resident microbiota or immune system
* Does not require a weakened host to cause disease
Opportunistic pathogens
* can only cause disease in situations that compromise the host’s defenses (e.g., weak immune system)
How Normal Microbiota Become Opportunistic Pathogens?
Conditions that provide opportunities for pathogens
* 1. Introduction of normal microbiota into unusual site in body
* 2. Immune suppression
* 3. Changes in the normal microbiota
* 4. Stressful conditions
What makes individuals susceptible to opportunistic infections?
- the very young,
- the elderly,
- women who are pregnant,
- patients undergoing chemotherapy,
- people with immunodeficiencies (such as acquired immunodeficiency syndrome [AIDS]),
- patients who are recovering from surgery,
- and those who have had a breach of protective barriers (such as a severe wound or burn).
Are all hosts at risk for opportunistic pathogens?
- Due to differences in host factors, a harmless species of the normal microbiota in one host may be pathogenic in another
For example:
* Group B streptococci (GBS) infections
* ~30% of women harbor GBS as normal commensals in the vagina
* Associated with sepsis, meningitis, and pneumonia in newborns
* Pregnant women are screened for GBS
What is the virulence factor
Characteristic or structure that contributes to the ability of a microbe to cause disease
What are the different types of Virulence factors?
- Adhesion factors
- Biofilms
- Extracellular enzymes
- Toxins
- Antiphagocytic factors
What are reservoirs?
- Sites where pathogens are maintained as a source of infection
- are an animate or inanimate habitat where the pathogen is naturally found
Define Endogenous source and Exogenous source
- Endogenous source means the pathogen came from the host’s own body
- Exogenous source means the pathogen is external to the host
Exogenous Sources
Environmental: contaminated food, medical equipment, soil, or water
Animals: transmit zoonotic diseases to people
Humans transmit communicable infections from one person to another
Endogenous Sources
Misplaced normal microbiota: Bacteria living harmlessly on skin can enter surgical incisions to cause postoperative infections.
Disrupted microbiota and opportunistic pathogens: For example, yeast in the vagina may proliferate and cause infection after antibiotics kill off bacterial neighbors.
What are three types of reservoirs
- Animal reservoir
- Human carriers
- Nonliving reservoir
What is an animal reservoir?
Zoonoses
* Diseases that naturally spread from animal host to humans
Acquire zoonoses through various routes
* Direct contact with animals or its waste
* Consumption of animals
* Bloodsucking arthropods: Vector
* Humans are usually dead-end host to zoonotic pathogens
* Difficult to eradicate
What is zoonosis?
- A. A disease caused by normal microbiota entering a body site where they do not normally occur
- B. A disease caused by changes in the balance between normal microbiota
- C. A disease caused by normal human microbiota from the respiratory tract
- D. A disease that spreads naturally from animals to humans
D. A disease that spreads naturally from animals to humans
What are human reservoirs?
- Human carrier:
- Infected hosts who are potential sources of infection for others
some infected people can remain both asymptomatic and infective for years.
*Types of carries
Active carrier has overt clinical case of disease
Convalescent carrier has recovered but continues to harbor large number of pathogen
Healthy carrier harbors the pathogen but is not ill (asymptomatic)
The incubatory carrier is incubating the pathogen in large numbers but is not yet ill
Passive carrier a healthy person whose body carriers the causal pathogen of an infectious disease although the person has not contracted the disease and remains symptomless
What are nonliving reservoirs?
- Soil, water, and food can be reservoirs of infection
- Presence of microorganisms is often due to contamination by feces or urine
- Soil: Clostridium bacteria, which can cause botulism, tetanus also toxoplasmosis, hookworms or gastrointestinal bacteria and viruses.
- Water: parasitic worm eggs, protozoa, bacteria and
- viruses.
- Food: meat and fruits harbors pathogens
The infectious agent is the animate or in animate habitat where the pathogen is naturally found.
* A. epidemic point
* B. emerging source
* C. contaminated source
* D. reservoir
D. reservoir
Define transmission.
Transmission is from a reservoir or a portal of exit to another host’s portal of entry
* How a pathogen spreads to a host
What are the three groups of transmission?
Three groups of transmission
* Contact Transmission
* Vehicle Transmission
* Vector transmission
What is contact transmission?
*Direct contact transmission
* Usually involves body contact between hosts
* Transmission within a single individual can also occur
Indirect contact transmission
* Pathogens are spread from host to host by fomites
Droplet transmission
* Spread of pathogens in droplets of mucus by exhaling, coughing, and sneezing
A blanket from a child with chickenpox is likely to be contaminated with the virus that causes chickenpox (Varicella-zoster virus). What is the blanket called?
* A. Host
* B. Pathogen
* C. Vector
* D. Fomite
D. Fomite
Vertical transmission, a specialized form of___________ occurs when the pathogen
passes from mother to offspring during pregnancy, during delivery, or through breast milk.
* A. direct contact transmission
* B. indirect contact transmission
* C. vehicle transmission
* D. airborne transmission
A. direct contact transmission
What is Vehicle Transmission?
Airborne transmission
* When pathogens travel more than 1 meter via an aerosol
* Sneezing, coughing, air-conditioning systems, sweeping
Waterborne transmission (Fecal-oral infection)
* Important in the spread of many gastrointestinal diseases
Foodborne transmission
* Pathogens in and on food
Bodily Fluid transmission
* Pathogens in blood, urine, saliva and other body fluids
What is Vector Transmission
Vectors: animals that transmit disease among hosts
Biological vectors
* Vector organism has a role in the pathogen’s life cycle
* Ex. Ticks and mosquitos
Mechanical vectors
* Passively transmit pathogens present on their body to new hosts
* Pathogen “hitches a ride” but doesn’t have part of its life cycle in the vector
* Ex. Flies, rodents and cockroaches
What is contamination?
The mere presence of microbes in or on the body
What is infection?
Organism (pathogens) evades the body’s external defenses, multiply, and become established in the body.
What is disease?
- invading pathogen alters normal body functions; adversely affect the body (cause damage)
- also referred to as morbidity
What is an infectious disease?
any disease caused by the direct effect of a pathogen
- Bacterial (plenty of infectious extracellular and intracellular bacteria)
- Viral (either DNA or RNA viruses and enveloped or non-enveloped)
- Fungal (eukaryotes, either unicellular or multicellular molds)
- Protozoal infections
- Helminths
What is the difference between the terms infection and disease?
* A. Infection refers to disease caused by microbes, while disease is the broader term used for any abnormal functioning of the body.
* B. Infection means that a pathogen has adhered to the body’s skin or mucous membranes, while disease means that the pathogen has invaded the body.
* C. Infection refers to the invasion of a pathogen into the body, while disease means that the body’s normal function is disrupted.
* D. Disease refers to the invasion of a pathogen into the body, while infection means that the body’s normal function is disrupted.
C. Infection refers to the invasion of a pathogen into the body, while disease means that the body’s normal function is disrupted
What are the steps to infection?
To establish an infection, a successful pathogen must complete five general tasks:
1. Enter the host
2. Adhere to host tissues
3. Invade tissues and obtain nutrients
4. Replicate while warding off immune defenses
5. Transmit to a new host
What are the three Portals of Entry?
Three major pathways
* Skin
* Mucous membranes
* Placenta
What is the purpose and characteristic of the portal of entry?
- An anatomic site through which pathogens can pass host tissue and enter the body
Three major pathways
* Skin
* Mucous membranes
* Placenta
Entry via the parenteral route circumvents the usual portals
Define the concept of infectious dose.
- that quantity of a pathogen (measured in number of organisms) that is necessary to cause infection in a susceptible host.
- ID50: Number of cells or virions needed to establish an infection in 50% of exposed hosts
- More infectious pathogens have a lower D50
- Measure virulence of a microbe
Define considerations.
The actual infective dose for an individual can vary widely, depending on factors such as route of entry; the age, health, and immune status of the host; and environmental and pathogen-specific factors such as susceptibility. to the acidic pH of the stomach.
What is more likely to cause disease pathogens with smaller or larger infectious doses?
Pathogens with smaller
Infectious dose (ID) will most easily cause disease
* Example:
The ID for Rickettsia is only one single cell.
The ID for gonorrhea is 1,000 bacteria.
Which pathogen will be the most virulent?
A 1,000 cell
B 320 cells
C 20 cells
D 150,000 cells
C. 20 cells
Which pathogen will be most likely to cause infectious disease?
A 1,000 cell
B 320 cells
C 20 cells
D 150,000 cells
C. 20 cells
What is the role and function of Adhesion in Infection?
Following the initial exposure, the pathogen adheres at the portal of entry.
Adhesion (attachment)
* The capability of pathogenic microbes to attach to the cells of the body using adhesion factors
Successful invasion requires adhesion
Different pathogens use various mechanisms to adhere to the cells of host tissues.
What are the factors in adhesion?
- fimbriae and glycocalyces (bacteria)
- suckers or hooks (helminths)
- adhesion disk (protozoa)
- Spikes and tail fibers (virus)
- Biofilms (bacteria)
Some pathogens have more than one adhesin, other can change their adhesins over time.
What is role of proteins and ligands in Adhesion of infection?
Attachment proteins and ligands help in adhesion
* Changing/blocking a ligand or its receptor can prevent infection
* Inability to make attachment proteins or adhesins renders microorganisms avirulent (harmless)
What do toxins and exoenzymes do when it comes to penetration?
Exoenzymes or toxins, which serve as virulence factors
* that allow them to colonize and damage host tissues as they invade and spread deeper into the body.
* that protect them against immune system defenses.
A pathogen’s specific virulence factor determine the degree of tissue damage that occur.
What is penetration and invasion into the host?
- Involves the dissemination of a pathogen through local tissue or the body
- Examples of virulence factors involved in penetration and invasion
- FLAGELLA
- EXTRACELLULAR ENZYMES (EXOENZYMES)
What are Three options for pathogen invasion?
Pathogen must invade tissues and obtain nutrients
- Flagella: motility enhances spread
- Extracellular Enzymes:
* important tool in bacteria identification
* secreted by the pathogen
* enable pathogens to dissolve structural
chemicals in the body and thereby maintaining an infection.
* To penetrate and invade deeper tissue
ex: Hyaluronidase, Kinases, Collagenase, Keratinase, Mucinase, Urease
How do the enzymes hyaluronidase and collagenase increase bacterial virulence?
* A. By digesting blood clots, resulting in invasion of damaged tissues
* B. By causing blood proteins to clot and providing a “hiding place” for bacteria
* C. By allowing bacteria to invade deeper into tissues, making the infection more likely to cause disease
* D. By digesting keratin, the main protein component of skin, allowing entry of the bacteria into the body
C. By allowing bacteria to invade deeper into tissues, making the infection more likely to cause disease
Which of the following applies to mucinase?
* A. is an antiphagocytic factor
* B. It promotes blood clotting
* C. It is produced by the host to target pathogens
* D. It is a virulence factor that promote the entry of the pathogen
D. It is a virulence factor that promote the entry of the pathogen
What is the purpose of evasion or avoidance of the host for pathogen?
Pathogens may also produce virulence factors that protect them against immune system defenses.
* Evade it
* Hide from it
* Inactivate it
Examples
-Antiphagocytic factors and chemicals
* Capsule and M protein
-Extracellular enzymes
* Leukocidins
* Peptidases
* IgA proteases
- Antigenic variation
- Intracellular growth
- Superantigens
- Suppression of immune system
What do Antiphagocytic Factors and Chemicals do.
- Factors that prevent phagocytosis by the host’s phagocytic cells
- Allow pathogens to remain in a host for longer time
- Bacterial capsule
* Composed of chemicals not recognized as foreign
* Slippery and difficult for phagocytes to engulf - Antiphagocytic chemicals
* Chemicals that prevent fusion of lysosome and phagocytic vesicles
* M protein
* Leukocidins directly destroy phagocytic white blood cells
Which type of virulence factor allows a pathogen to break down a blood clot that the body has
generated to trap their spread?
* A) leukocidins
* B) hyaluronidase
* C) collagenase
* D) kinase
* E) coagulase
D) kinase
What are Toxins?
- biological poisons that assist the pathogen in their ability to invade and cause damage to tissues
- Chemicals that harm tissues or trigger host immune responses that cause damage
- Often responsible for majors symptoms of bacterial infection
What are two types of toxins?
- Exotoxins
- Endotoxins
What is an endotoxin?
- Only Gram negative
- Also know as Lipid A
- Release during cell division, during phagocytosis and when the cells dies
- Can cause excessive inflammatory response, leading to fever, severe drop in blood pressure, multi-organ failure, and death.
What is an exotoxin?
- Gram positive (primary) and Gram negative
- A bacterial protein that is secreted by a living bacterium into its surroundings
- Grouped into three categories:
Cytotoxins, neurotoxins, and enterotoxins
Diseases caused by exotoxins
You have recently identified a new toxin. It is produced only by gram-negative bacterium. It is found in the outer membrane of gram-negative bacteria. It could be fatal in high doses. Based on these characteristics, how would you classify this toxin?
a) superantigen
b) Endotoxin
c) Exotoxin
d) leukocidin
b) Endotoxin
What effect do enterotoxins have?
* A. They affect the nervous system.
* B. They kill any of the host cells they enter.
* C. They affect the gastrointestinal system.
* D. They are released from Gram-negative bacteria and can cause fever, inflammation, hemorrhaging, shock, and blood coagulation.
C. They affect the gastrointestinal system.
What are virulence factors, and why are they key?
Discovering virulence factors of pathogenic microbes is a key in understanding pathogenesis, diagnosis and for identification of targets for novel drugs and design of new vaccines.
Virulence Factors
* Adhesion Factors
* Extracellular Enzymes (invasion and penetration)
* Competition for nutrients
* Resistance of host defenses
(evade, hide, inactivate)
* Secretions of toxins
What are the five stages of infectious disease?
- Incubation period
- Prodromal period
- Illness
- Decline
- Convalescence
Characteristic of each phase of infectious diseas.
Incubation period: (No signs or symptoms)
Prodromal Period: Vague, general symptoms
Illness: Most severe signs and symptoms
Decline: declining signs and symptoms
Convalescence: No signs or symptoms
What are the two measures of the stages of the disease?
Intensity of signs or symptoms (y-axis)
Time (x-axis)
What stage is a patient infectious during.
Patient is infectious during every stage of the disease.
Not every stage occurs in every disease.
Define Symptoms
Subjective characteristics of disease felt only by the patient.
Define Signs
Objective manifestations of disease observed or measured by others
Define Syndrome
Symptoms and signs that characterize a disease or abnormal condition
Asymptomatic, or subclinical,
Asymptomatic, or subclinical, infections lack symptoms but may still have signs of infection
In what way do symptoms facilitate transmission to others?
Sometimes the symptoms a pathogen generates facilitate transmission to others
* Itchiness
* Sneezing
* Coughing
* Diarrhea
What is an example of a sign (as opposed to a symptom) of disease?
* A. Nausea
* B. A headache
C. A rash
D. Dizziness
C. A rash
How can disease be classified?
Taxonomic categories
* Gram-positive or gram-negative bacteria, fungi, DNA or RNA viruses
The body system they affect
* Diseases of the Nervous System…
Their longevity and severity
* Acute vs. chronic diseases…
How they are spread to their host
* Communicable vs. no-communicable
The effects they have on populations
* Epidemiology
Portals of exit
*Many portals of exit are the same as portals of entry
*Pathogens often leave hosts in materials the
body secretes or excretes
