Lecture 22: Bacterial pathogenesis I Flashcards
What is an infection?
When a pathogen becomes established in the body via invasion or colonization.
What is disease?
An infection which produces signs and symptoms and prevents the body from performing normal functions (abnormal state).
What is the difference between a symptom and a sign?
A symptom is a subjective characteristic felt only by the patient, while a sign is an objective manifestation observed or measured by others.
What is pathogenesis?
The development of disease
Infection without disease is called […]
Asymptomatic carriage
How does helicobacter pylori grow and what signs/symptoms does it cause?
It grows in the stomach acid by produce urease. It disrupts stomach mucosa, causing inflammation and gastric ulcers. It can also cause gastric cancer. However, the majority of people who ingest the bacteria are asymptomatic.
Is helicobacter pylori gram negative or gram positive?
It is gram negative.
The only bacteria to be classified as a carcinogen is […], because […]
H. pylori, it is strongly linked to stomach cancer
Name the 3 major types of pathogens on the pathogen spectrum from least to most harmful.
Probiotics: beneficial or commensal
Pathobionts: can be harmful, opportunistic
Pathogens: harmful
What are Koch’s 4 postulates?
- Microorganism found in abundance in all organisms with the disease and not in healthy organisms
- Microorganism should be isolated from diseased organism and grown in pure culture
- The pathogen from the pure culture must cause the disease when introduced into a healthy organism
- Microorganism must be re-isolated from the host of step 3 and identified as being identical to the original isolate.
If a bacterium fulfills Koch’s postulates, it can be considered […]
Pathogenic
Describe a caveat to Koch’s first postulate.
Postulate: microorganism found in abundance in all organisms suffering from the disease and not in healthy individuals.
Caveat: Some pathogens may be isolated from healthy individuals without disease, some diseases have multiple causes
Describe a caveat to Koch’s second postulate.
Postulate: Microorganism should be isolated from diseased organism and grown in pure culture.
Caveat: some organisms are hard/impossible to culture.
Describe a caveat to Koch’s third postulate.
Postulate: Cultured microorganism should cause the disease when introduced into a healthy organism.
Caveat: disease can depend on the health status of the host, genetics of the host, environmental factors, site of introduction, etc.
Name 3 pathogen factors that can affect the outcome of a host/bacteria interaction.
- Number
- Route
- Virulence potential
Name 5 host factors that can affect the outcome of a host/bacteria interaction.
- Genetics
- Nutritional status
- Immune status
- Other infections
- Microbiome status.
What is a secondary infection?
An infection that develops in an individual who is already infected with a different pathogen.
Give an example of a secondary infection.
Tuberculosis is a major cause of death in patients with AIDS.
Explain how pseudomonas aeruginosa infects people.
It colonizes the skin and intestinal tract. Normally, our immune system can fight it off, but people with cystic fibrosis can’t. They have thick mucous in their lungs that prevents them from clearing the bacteria, so P. aeruginosa is a major cause of death in CF patients. P. aeruginosa is an opportunistic pathogen.
Explain how our microbiome affects C. difficile infection.
If we take antibiotics, this can involve the killing of good bacteria in our microbiome that would normally fight off C. difficile.
Name the 6 steps involved in the pathogenesis of bacteria diseases.
- Maintain a reservoir
- Be transported to the host
- Adhere to, colonize, and/or invade host
- Multiply or complete life cycles on or in host
- Evade host defenses
- Leave host and return to reservoir or enter new host
What is the reservoir of an infectious agent?
It is the habitat in which the agent normally lives, grows, and multiplies. It is not the same as a host, which gets infected by the agent.
Reservoirs can be […]
Humans, animals, and the environment
What is a carrier?
A person is a seeminly uninfected person/animal/etc who is capable of transmitting the pathogen to others.
Name the reservoir associated with:
a) Salmonella typhi
b) Enterohemorrhagic E. coli
c) Salmonella
d) Campylobacter
e) Clostridium tetani
a) Typhoid Mary
b) Cow
c) Poultry
d) Poultry
e) Soil
What are the two major types of transport of the bacterial pathogen to a host?
Direct and indirect.
What are the two major types of direct transport of pathogens to a host?
Direct contact and droplet spread.
Give 3 examples of direct contact.
Skin-skin, kissing, sexual contact
Give 3 examples of droplet spread.
Sneezing, coughing, talking
What are the 3 major types of indirect transport of pathogens to a host?
Airborne, vehicle-borne, vector-borne
What is airbone indirect transport of a pathogen to a host?
It involves small particles that are suspended in the air for long periods.
Give 3 examples of vehicle-born indirect transport of a bacterial pathogen to a host.
Food/water, biological products (blood), fomites (objects such as handkerchiefs, bedding, or scalpels)
Give 3 examples of vector-borne transport of a pathogen to a host.
Living beings: mosquitoes, fleas, and ticks
What is adherence?
It is the process by which microoganisms attach themselves to cells. This is required for colonies to successfully establish themselves in the host.
Adherence is made possible by […]
Adhesins
What are adhesins? Include their function and what they’re made of.
They are molecules or structures that allow for the adherence of microorganisms to the host and dictate the susceptibility of the host. They are made of proteins, glycoproteins, or glycolipids. There are many types that exist.
Name 4 different examples of bacterial adhesins.
Non-fimbrial, fimbriae, type 4 pilli, curli
What is colonization?
The growth of microorganisms after they’ve gained access to host tissues, after adherence
Where does colonization take place?
It starts either in mucous membrane or in tightly packed epithelial cells coated in mucus, a thick liquid secretion of glycoproteins.
What are the 3 types of bacterial invasion?
Active into host cells, active between host cells, and passive.
Explain how active invasion into host cells works.
The bacteria cause the host to produce proteins that will allow it to colonize.
Explain how active invasion between host cells works.
The bacteria colonize between the junctions separating host cells.
Explain how passive invasion works.
This can happen when you have an insect bite, lesion, etc. The bacteria just goes into the host and colonizes without having to do anything. It can use existing host pathways for internalization, such as phagocytosis.
When does multiplication/complete life cycles occur?
It occurs when pathogens finds an appropriate environment in the host in terms of nutrients, pH, temperature, and protection from host immune system.
Which type of cells do intracellular pathogens tend to invade? Why?
They tend to invade immune cells, because once they are compromised, the body is left defenseless.
Describe how bacteria evade host defenses.
They secrete proteins that can deactivate host defenses and have bacterial capsules.
Name 3 functions of bacterial capsules.
- Can evade host defenses by making it difficult for phagocytes to engulf them.
- Can facilitate attachment on host tissues (adherence step)
- Are composed of chemicals not recognized as foreign by the host
Why is the leaving the host step necessary?
It is must occur for the microbe to be perpetuated.
How do most bacteria leave their host? Give examples.
They mostly leave by passive mechanisms, such as feces, urine, droplets, saliva, or desquamated cells. Symptoms of disease such as coughing, sneezing, and diarrhea help in this process.
