WEEK 2: BACTERIAL PATHOGENICITY Flashcards
What is symbiosis?
All associations in which one species lives in or on the body of another.
-living together!!
Symbiosis is a fundamental concept in ecology and the study of interspecific relationships. There are several types of symbiotic relationships, including.
State The 3 types of symbiotic relationships.
Mutualism:
In mutualistic symbiosis, both species involved benefit from the relationship. This can involve mutual exchange of resources or services.
For example, pollination is a classic example of mutualism, where plants provide nectar to pollinators (like bees) in exchange for the transportation of pollen to other flowers, aiding in reproduction.
Commensalism:
In commensalism, one species benefits from the interaction, while the other species is neither helped nor harmed.
An example is the relationship between barnacles that attach to the shells of sea turtles. The barnacles benefit from being transported to new feeding areas while the turtles are not significantly affected.
Parasitism:
Parasitic symbiosis involves one species (the parasite) benefiting at the expense of the other species (the host), which is harmed by the interaction.
Common examples include parasitic worms or bacteria that live within a host organism and derive nutrients from the host’s tissues.
Amensalism:
Amensalism is a type of symbiosis where one species is negatively affected (harmed or inhibited) by the presence of another species, which is not significantly influenced in return.
For example, some plants release chemicals into the soil that inhibit the growth of nearby plants.
Predation:
While not always classified as a symbiotic relationship, predation is another ecological interaction where one species (the predator) hunts and consumes another species (the prey). This interaction is crucial for controlling population sizes and regulating ecosystem dynamics.
Define the following terms:
Commensal
Pathogen
Opportunistic pathogen
Commensal: One species of organism lives
harmlessly and in complete harmony in or on the
body of a larger species
❖ without causing any damage or disease
❖ part of the normal flora
Pathogen: A microorganism that lives on or in the
host and capable of causing disease.
Opportunistic pathogen: An agent capable of
causing disease only when the host’s resistance is
impaired
Define the following terms:
Infection
Disease
Pathogenesis
- Infection -
Any situation in which a microorganism is established and growing in a host, whether or not the host is harmed.
- Disease is a damage or injury to the host that impairs host function.
- Pathogenesis refers both to the mechanism of infection and to the mechanism by which disease develops.
o It refers to the sequence of events in the response of cells or tissues to the etiologic agent, from the initial stimulus to the ultimate expression of the disease.
What is infectivity?
What is infectious dose (ID50)?
Ability of a pathogen to establish an infection and its capacity for transmission.
Infectivity -positively correlate with virulence.
Infectious dose 50 (ID50): is the dose or
numbers of the agent required to infect 50% of
animals in a test group
What is virulence?
What is lethal dose 50 (LD50)?
The quantitative measure of pathogenicity or harmfulness of an infectious agent.
It measures the severity of the disease or damage caused by the agent once it has successfully infected a host.
Relative ability of a pathogen to harm the
host.
Lethal dose 50 (LD50)- the dose of an agent
that can kill 50% of the animals in a test group.
What is the difference between infectivity and virulence?
“infectivity” relates to the initial capability of an infectious agent to enter and infect a host, while
“virulence” pertains to the harmfulness or severity of the disease caused by the agent once it has successfully established an infection.
Describe the “iceberg” concept of infectious disease.
Tip of the Iceberg (Clinical Cases):
The “tip” of the iceberg represents the cases of an infectious disease that are clinically apparent and diagnosed.
These are individuals who exhibit symptoms, seek medical attention, and are officially recognized as having the disease.
These cases are typically documented, reported, and included in official disease statistics.
Below the Surface (Subclinical and Unrecognized Cases):
Beneath the water’s surface, the “iceberg” represents the subclinical or unrecognized cases of the disease.
This category includes individuals who are infected with the pathogen but do not show symptoms or have mild, non-specific symptoms that may not lead them to seek medical care.
Some of these individuals may eventually develop symptoms, while others may remain asymptomatic throughout the course of their infection.
Whatare virulence factors?
Expression of virulence determinants are carefully regulated involves a form of chemical communication between bacteria known as _____________.
Factors that allow microorganisms to:
invade the host cell.
damage the host cells.
resist the defenses of the host.
- Expression of virulence determinants are carefully regulated involves a form of chemical communication between bacteria known as quorum sensing.
Outline mechanisms of acquiring bacterial virulence genes
- Horizontal Gene Transfer (HGT):
HGT is a major mechanism for acquiring virulence genes.
It involves the transfer of genetic material from one bacterium to another that is not its offspring. The primary methods of HGT include:
*Conjugation:
*Transformation:
*Transduction:
- Genomic Islands: Genomic islands are large segments of bacterial DNA that have been acquired through HGT and often contain virulence genes. These islands can integrate into the bacterial chromosome and become a permanent part of the genome.
- Plasmids and Mobile Genetic Elements:
Plasmids are small, circular pieces of DNA that can carry virulence genes and transfer them between bacteria.
They are considered mobile genetic elements and can move between different bacterial species.
- Integration of Prophages:
Some bacteria have temperate phages, which can integrate their DNA into the bacterial genome. This integration can sometimes bring with it virulence genes or alter the host’s gene expression to enhance virulence.
- Transposons: Transposons are genetic elements that can move within the bacterial genome. They may contain virulence genes or promote their transfer by facilitating recombination events.
- Gene Duplication and Divergence:
In some cases, virulence genes may arise through gene duplication events followed by divergence. A duplicated gene may acquire mutations that enable it to perform a new function associated with virulence.
- Mutations and Adaptations: Bacteria can acquire virulence by accumulating mutations over time. These mutations can lead to the expression of new virulence factors or the loss of factors that restrict pathogenicity.
- Genetic Rearrangements: Genetic rearrangements, such as inversions, deletions, or insertions, can result in the acquisition of virulence genes or the activation of silent virulence genes already present in the genome.
It’s important to note that not all bacteria with virulence genes are pathogenic, as the expression and regulation of these genes are influenced by various factors, including environmental conditions, host interactions, and the bacterium’s genetic background. Additionally, the presence of virulence genes does not guarantee the immediate development of disease; it is often a multifactorial process that depends on the interplay of multiple factors.
What are pathogenicity islands?
Pathogenicity islands are large genetic regions in the chromosome or on plasmids that contain sets of genes encoding numerous virulence factors that may require coordinated expression.
List the potential sources and possible routes of infection by bacteria.
- Human: Tuberculosis, Typhoid, Syphilis
- Animals: Anthrax, Tuberculosis, Brucellosis
- Insects: Plague, Typhus, Relapsing fever
- Soil, water: Tetanus, Cholera, Typhoid, Dysentery
- Food: Staphylococcus, food poisoning, Salmonellosis
Outline methods of transmission.
Contact
*Kissing
*Shaking hands
*Vertical
*Vector
*Animal
Indirect
*Fomites
*Vehicles
*Air
*Fecal-oral
Outline 3 ways in which Infectious agents establish infection and damage tissues.
- They can come into contact or enter host cells and directly cause cell death.
- They may release
I. Toxins that kill cells at a distance
ii. Enzymes that degrade tissue components, damage blood vessels and cause ischemic necrosis. - Induce host immune responses (a double-edged sword!)
What is microbial pathogenesis?
Microbial Pathogenesis: Process by which organisms cause disease.
Describe the process of microbial pathogenesis.
- Exposure to pathogens
- Adherence to skin or mucosa
- Invasion into epithelium
- Colonization and growth: Production of virulent factors
- Toxicity
- Invasiveness and metastasis
- Tissue damage and disease
Give examples of bacterial pathogens transmitted by different routes and outline the ways in which they cause disease.
- Ingestion: Salmonella spp., Shigella spp., Yersinia enterocolitica, enterotoxigenic Escherichia coli, Vibrio spp., Campylobacter spp., Clostridium botulinum, Bacillus cereus, Listeria spp., Brucella spp.
- Inhalation
Mycobacterium spp., Nocardia spp., Mycoplasma
pneumoniae, Legionella spp., Bordetella, Chlamydophila psittacine, Chlamydophila pneumoniae, Streptococcus spp. - Trauma /Skin
Clostridium tetani, Clostridium perfringens,
Staphylococcus aureus, Streptococcus spp, Bacillus
anthracis, Pseudomonas spp. - Arthropod bite: Rickettsia, Ehrlichia , Coxiella, Francisella , Borrelia spp., Yersinia pestis
- Sexual transmission: Neisseria gonorrhoeae, Chlamydia trachomatis, Treponema pallidum
What are the following adherence factors?
A surface structure or macromolecule that binds a bacterium to a specific surface.
A complementary macromolecular binding site on a (eucaryotic) surface that binds specific adhesins or ligands.
A surface molecule that exhibits specific binding to a receptor molecule on another surface
Any protein that binds to a carbohydrate
The mucopolysaccharide layer of glycosaminoglycans covering animal cell mucosal surfaces.
Filamentous proteins on the surface of bacterial cells that may behave as adhesins for specific adherence.
Same as fimbriae
A specialized pilus that binds mating procaryotes together for the purpose of DNA transfer.
Fimbriae in Enterobacteriaceae which bind specifically to mannose terminated glycoproteins on eucaryotic cell surfaces.
Adhesin: A surface structure or macromolecule that binds a bacterium to a specific surface.
Receptor: A complementary macromolecular binding site on a (eucaryotic) surface that binds specific adhesins or ligands.
Ligand: A surface molecule that exhibits specific binding to a receptor molecule on another surface
Lectin: Any protein that binds to a carbohydrate
Mucous: The mucopolysaccharide layer of glycosaminoglycans covering animal cell mucosal surfaces.
Fimbriae: Filamentous proteins on the surface of bacterial cells that may behave as adhesins for specific adherence.
Common pili: Same as fimbriae
Sex pilus: A specialized pilus that binds mating procaryotes together for the purpose of DNA transfer.
Type 1 fimbriae: Fimbriae in Enterobacteriaceae which bind specifically to mannose terminated glycoproteins on eucaryotic cell surfaces.
