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Questions and Answers

What does pathogenicity refer to?

Differences between microbial species (correct)

The severity of the disease caused by a strain

The ability to evade the immune system

The environmental factors affecting bacteria

What is virulence specifically related to?

Differences between strains of the same species (correct)

The total number of bacteria in an environment

The genetic diversity of bacteria

The diversity of microbial species in a habitat

Which of the following is NOT a step necessary for an organism to cause disease?

Harm the host

Colonize the host body

Maintain a reservoir of infection

Increase host immunity (correct)

Which of the following is a factor that promotes bacterial colonization in the host?

Contact with host cells Signup and view all the answers

What role do virulence factors that damage the host play?

Disrupt host cellular processes Signup and view all the answers

What is one way bacteria can resist innate immune defenses?

By evading phagocytosis Signup and view all the answers

How do motile bacteria improve their chances of colonization?

By swimming towards mucosal surfaces Signup and view all the answers

What factor influences whether a person contracts an infectious disease?

The number of bacteria and host immune defenses Signup and view all the answers

What allows spirochetes to penetrate host mucous membranes more effectively?

Their thinness and motility Signup and view all the answers

What mechanism does Helicobacter pylori use to protect itself from stomach acid?

Secreting an acid-inhibitory protein Signup and view all the answers

What is one outcome of the inflammatory response triggered by Helicobacter pylori?

Destruction of mucus-secreting membranes Signup and view all the answers

What function does streptokinase serve in the infection process of Streptococcus pyogenes?

Lyses fibrin clots Signup and view all the answers

How do bacteria resist being physically removed from the body?

By producing pili and biofilms Signup and view all the answers

What type of immune response is triggered by Helicobacter pylori in the stomach?

Massive inflammatory response Signup and view all the answers

What is the result of the damage to the gastric mucosa caused by Helicobacter pylori?

Formation of gastric and duodenal ulcers Signup and view all the answers

What role does DNase play in the pathogenicity of Streptococcus pyogenes?

Degrades cell-free DNA in pus Signup and view all the answers

What process allows bacteria to activate genes involved in virulence upon attachment to host cells?

Signal transduction Signup and view all the answers

What enables certain bacteria to evade antibodies by genetically altering their pili?

Adhesive capacity Signup and view all the answers

Which of the following are proteins that enable bacteria to adhere to host cells?

Adhesins Signup and view all the answers

What structure do many bacteria form on host tissue to enhance adherence and protection?

Biofilms Signup and view all the answers

Which invasin enables Streptococcus pneumoniae to enter host cells and resist phagocytosis?

Phosphorylcholine Signup and view all the answers

What is a common role of invasins produced by bacteria?

Enabling bacterial entry into host cells Signup and view all the answers

The ability to compete for nutrients directly relates to what aspect of pathogenic bacteria?

Pathogenicity Signup and view all the answers

Which of the following is NOT associated with bacterial virulence?

Personal immunity Signup and view all the answers

What is one reason bacterial generation time is slower in the body than in lab culture?

Limited essential nutrients Signup and view all the answers

What are pathogen-associated molecular patterns recognized by during unenhanced attachment?

Endocytic pattern-recognition receptors Signup and view all the answers

What do pathogens need to do to establish infections effectively?

Compete for limited nutrients Signup and view all the answers

What is the process called when IgG or complement proteins enhance the attachment of microbes to phagocytes?

Opsonization Signup and view all the answers

What are siderophores?

Iron-chelating compounds produced by bacteria Signup and view all the answers

How do bacteria compete for iron in the body?

By synthesizing iron chelators Signup and view all the answers

Which of the following is a component of the complement pathways?

C3b Signup and view all the answers

What is the function of lysosomes in phagocytosis?

To fuse with phagosomes and destroy microbes Signup and view all the answers

What does the body produce to limit free iron availability?

Iron chelators like transferrin Signup and view all the answers

How many complement pathways are there in total?

Three Signup and view all the answers

What happens when iron concentrations are low in the body?

Bacteria produce exotoxins targeting host cells Signup and view all the answers

What must occur before a phagocyte can engulf a microbe?

The microbe must attach to the phagocyte's membrane Signup and view all the answers

Which function is NOT performed by activated complement proteins?

Antibody production Signup and view all the answers

What do many pathogenic bacteria do to utilize the iron from other bacteria?

They develop receptors for siderophores of other bacteria Signup and view all the answers

What role do capsules play for certain bacteria in relation to phagocytosis?

Enable resistance to phagocytic engulfment Signup and view all the answers

What is the first step in the process of phagocytosis?

Attachment of the microbe Signup and view all the answers

What role do capsules play in bacterial resistance to phagocytosis?

They block the attachment of bacteria to phagocytes. Signup and view all the answers

How does coagulase contribute to bacterial evasion of the immune system?

By forming fibrin clots around the organism. Signup and view all the answers

What does the Type III secretion system do for bacteria?

It delivers proteins directly into the host cytoplasm. Signup and view all the answers

Which of the following is a method bacteria use to evade antibody responses?

Changing the adhesive tips of their pili. Signup and view all the answers

What is one way bacteria prevent the fusion of phagosomes with lysosomes?

Producing pore-forming proteins. Signup and view all the answers

How do some bacteria avoid detection by antibodies due to their capsule?

By having capsules that some antibodies cannot recognize. Signup and view all the answers

What is a method bacteria use to resist phagocytic destruction?

They escape from the phagosome into the cytoplasm. Signup and view all the answers

Why might bacteria vary their surface proteins?

To evade host immune responses. Signup and view all the answers

Study Notes

Pathogenicity & Virulence

Pathogenicity and virulence describe an organism's ability to cause disease.
Pathogenicity refers to differences between microbial species.
Virulence refers to differences between strains of the same species.
In practice, they are often used interchangeably.

To Cause Disease

An organism must:
- Maintain a reservoir (e.g., humans, animals, environment) before and after infection.
- Leave the reservoir and access a new host.
- Colonize the new host's body.
- Harm the body.

Influences

Factors that influence the organism's ability to cause disease include its structures and metabolic products.
Whether or not a person contracts a disease depends not only on the microorganism but also on the number of bacteria that enter the body and the quality of the individual's immune defenses.

Virulence Factors

Bacterial virulence factors are divided into two categories:
- Factors that promote bacterial colonization of the host.
- Factors that damage the host.

Virulence Factors Promoting Colonization

These factors enable bacteria to:
- Contact host cells.
- Adhere to host cells and resist physical removal.
- Invade host cells.
- Compete for iron and other nutrients.
- Resist innate immune defenses (e.g., phagocytosis).
- Evade adaptive immune defenses.

Ability to Contact Host Cells

Motile bacteria that can swim chemotactically toward mucosal surfaces have a better chance to contact mucous membranes, attach, and colonize; mucosal surfaces (e.g., bladder, intestines) constantly flush bacteria away to prevent colonization.
Spirochetes, due to their thinness, internal flagella, and motility, are more readily able to penetrate host mucous membranes, skin abrasions, etc., enter the body and disseminate to other body sites.

Ulcers: H. pylori

Helicobacter pylori swims through the stomach's mucus layer and adheres to the epithelial cells.
To protect itself from stomach acid, it produces an acid-inhibitory protein.
The bacterium then releases toxins damaging the gastric mucosa.
This leads to a massive inflammatory response with leukocytes killing bacteria, but also damaging the mucus membranes.
Without the mucus layer, gastric acid causes stomach ulcers.

Streptococcus pyogenes

Streptococcus pyogenes produces streptokinase to lyse fibrin clots, allowing the infection to spread.
The bacterium also produces DNase that degrades cell-free DNA in pus and reduces its viscosity.
Both enzymes facilitate spread to new tissues.

Ability to Adhere to Host Cells and Resist Physical Removal

The body's innate defenses physically remove bacteria through shedding of surface epithelial cells, coughing, sneezing, vomiting, diarrhea, and bodily fluids (e.g., saliva, blood, mucus, urine).
Bacteria may resist physical removal by producing pili, cell wall adhesins, and/or biofilm-producing capsules.

Signal Transduction

Physical attachment of bacteria to host cells can signal the activation of virulence-related genes.
This is known as signal transduction.

Pili and Bacterial Adherence

Some bacteria alter the adhesive tips of their pili to adhere to and colonize different cell types with diverse receptors and evade antibodies.

Adhesins

Adhesins are proteins in the cell walls of various bacteria.
They bind to specific receptor molecules on host cells, enabling intimate attachment, colonization, and resistance to physical removal.
Many bacteria utilize one or more adhesins for colonization.
Bordetella pertussis produces multiple adhesins.

Capsules and Biofilms

Many normal flora bacteria produce a capsular polysaccharide matrix or glycocalyx.
This forms a biofilm on host tissues.
Biofilms are layers of bacterial populations adhering to host cells.
Embedded in a common capsular mass, they are found in situations like dental plaque and inner ear infections.

Ability to Invade Host Cells

Some bacteria produce adhesin molecules called invasins.
These activate the host cell's cytoskeletal machinery, enabling bacterial entry by phagocytosis.
Bacteria entering the cytoplasm are protected from complement, antibodies, and other body defenses.

Examples

Streptococcus pneumoniae produces phosphorylcholine, an invasin enabling entry to cells and resisting phagocytosis.
Streptococcus pyogenes's F and M proteins aid invasion of epithelial cells and maintain persistent infections.

Ability to Compete for Iron and Other Nutrients

Pathogenicity is related to the bacterium's ability to successfully compete with host tissue and normal flora for limited nutrients.
The generation time of bacteria in the body is typically slower than in a lab culture due to limited nutrients.

Nutritional Competition

To be pathogenic, a bacterium must multiply in host tissue.
The rate of bacterial replication is correlated with the probability of infection establishment.
Bacteria compete for nutrients: synthesis of specific transport systems or cell wall components aiding nutrient uptake.
Bacteria compete for iron, where the host body also makes adjustments to deprive the microorganism of this essential nutrient.

Siderophores

Bacteria synthesize iron chelators called siderophores.
Many siderophores are excreted and re-enter the cell to bind iron.
Others are found on the cell wall, binding and transporting the iron into the bacterium.
The concentration of free iron is low due to host-produced iron chelators.

Other Ways of Acquiring Iron

Some bacteria produce receptors for siderophores from other bacteria, taking iron from them.
Some pathogenic bacteria bind human iron-binding proteins like transferrin, lactoferrin, ferritin, and hemin as the iron source.
Bacteria can secrete exotoxins to kill host cells, accessing iron if concentrations are low.

Resist Innate Immune Defenses

Overview of Phagocytosis: The microbe surface must attach to the phagocyte's cytoplasmic membrane for ingestion.
Unenhanced attachment generally recognizes pathogen-associated molecular patterns in microbial cell walls, not found on human cells.
These patterns are recognized via endocytic pattern-recognition receptors on phagocytes.

Enhanced Attachment

Enhanced attachment occurs through antibody molecules (e.g., IgG) or complement proteins (e.g., C3b, C4b) called opsonins that promote attachment.
This process, known as opsonization, is more specific and efficient than unenhanced attachment.

Phagocytosis Continued

Following attachment, polymerization and depolymerization of actin filaments forms pseudopods to engulf the microbe into a phagosome.
Lysosomes fuse with the phagosome, digesting and destroying the microbe.

Complement Pathways

Bacteria can interfere with the body's complement pathways.
There are three pathways: classical, alternative, and lectin.
These pathways, though activated differently, all produce beneficial complement proteins.

Complement Proteins

Complement proteins are a set of serum proteins.
When activated, they participate in: inflammation, phagocyte chemotaxis, opsonization, and lysis of membranes.

Capsules

Capsules enable organisms to resist phagocytic engulfment.
Capsules of some bacteria interfere with the body's complement pathways.

Other ways to resist phagocytosis

Coagulase induces fibrin clot formation, which helps to resist phagocytosis.
Pathogenic Yersinia, using a type III secretion system, delivers proteins that depolymerize actin microfilaments, needed for phagocytic engulfment.

The Type III Secretion System

The bacterium produces pore-forming proteins that create a pore spanning the bacterium's and outer membrane and the host cell's plasma membrane.
The system allows the bacterium to directly deliver proteins into the host cell cytoplasm.

Bacteria Resisting Phagocytic Destruction

Escape from the phagosome into the cytoplasm prior to phagosome/lysosome fusion.
Preventing phagosome/lysosome fusion by inserting por proteins.
Producing enzymes that kill the phagosome.

Evading Adaptive Immune Defenses

A major defense against bacteria is antibody production, with antibody tips (Fab regions) having shapes complementary to the bacterial proteins and polysaccharides (epitopes).

Avoiding Antibodies

Bacteria alter adhesive tips of pili or surface proteins to avoid antibodies.
Antibodies may not be made against some capsules.
Bacteria coat themselves with host proteins like fibronectin, lactoferrin, or transferrin to avoid antibody binding.

Virulence Factors Damaging the Host

The ability to produce cell wall components (PAMPs) that cause host cells to produce inflammatory cytokines.
The production of harmful exotoxins.
The ability to induce autoimmune responses.

Autoimmunity and Exotoxins

Autoimmunity occurs when the body's immune defenses mistakenly attack the body (trigger often bacteria).
Exotoxins are protein toxins secreted by living bacteria or released upon lysis.
Three types:
- Superantigens (Type I toxins).
- A-B toxins and other toxins interfering with host cell function (Type III toxins).
- Exotoxins damaging host cell membranes (Type II toxins).

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