Introduction to Bacterial Pathogenesis

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Questions and Answers

What defines pathogenicity in bacteria?

The ability to grow in the presence of oxygen

The ability to cause disease (correct)

The ability to adhere to host tissues

The ability to produce toxins

Which of the following statements about strict pathogens is true?

They can only cause disease in individuals with weakened immune systems.

They are more virulent and can cause diseases in a normal person. (correct)

They primarily live in a symbiotic relationship with their host.

They are less virulent than opportunistic pathogens.

What is the role of virulence factors in microorganisms?

To contribute to an organism’s virulence (correct)

To reduce the likelihood of disease transmission

To enhance the replication rate of bacteria

To eliminate the host's immune response

Which term describes the scientific study of disease?

Pathology Signup and view all the answers

Which of the following is NOT a portal of entry for pathogens?

Ocular route Signup and view all the answers

What is the most common route of infection through mucous membranes?

Respiratory tract Signup and view all the answers

Which of the following conditions is most commonly associated with the gastrointestinal route of infection?

Cholera Signup and view all the answers

What is the primary function of unbroken skin in relation to microorganisms?

It acts as a barrier to most microorganisms. Signup and view all the answers

What does the term ID50 refer to?

The infectious dose required to produce an infection in 50% of test animals. Signup and view all the answers

Which pathogen is known to enter the body through the parenteral route?

HIV Signup and view all the answers

What does LD50 measure in relation to toxins?

The lethal dose for 50% of a sample population Signup and view all the answers

Which of the following statements about ID50 is true?

A lower ID50 indicates higher virulence of a microorganism. Signup and view all the answers

What role do ligands and adhesins play in microbial infection?

They bind specifically to receptors on host cells. Signup and view all the answers

Which of the following examples illustrates adherence of microorganisms?

Streptococcus mutans attaching to dental surfaces via glycocalyx Signup and view all the answers

How does altering either the receptor or the adhesin affect infection?

It decreases the possibility of the infection occurring. Signup and view all the answers

What is the primary role of adhesins on fimbriae in bacteria?

To facilitate attachment to host tissues Signup and view all the answers

How do biofilms contribute to bacterial survival?

They create a protective barrier against host defenses Signup and view all the answers

Which of the following mechanisms does not assist in bacterial survival in the host?

Siderophore production Signup and view all the answers

What impact does the capsule have on phagocytosis?

Impairs phagocytosis Signup and view all the answers

Which of the following statements about M proteins is accurate?

M proteins mediate attachment and resist phagocytosis Signup and view all the answers

What type of immune response is provoked by superantigens?

Intense immune response Signup and view all the answers

What function do coagulase enzymes serve for bacteria?

They isolate microorganisms from host defenses Signup and view all the answers

Antigenic variation alters what aspect of pathogens?

Surface proteins Signup and view all the answers

What is the main effect of botulinum toxin on the body?

Inhibits nerve impulse transmission Signup and view all the answers

Which type of toxin is characterized by being a poisonous compound produced by microorganisms?

Exotoxin Signup and view all the answers

Which of the following best describes the action of diphtheria toxin?

Inhibits protein synthesis Signup and view all the answers

What is the definition of toxemia?

The presence of toxins in the host's blood Signup and view all the answers

What is the role of IgA proteases in bacterial pathogenicity?

To destroy antibodies Signup and view all the answers

Which type of toxin primarily attacks cardiac cells?

Cardiotoxins Signup and view all the answers

What role do erythrogenic toxins play in disease?

Damage plasma membranes of capillaries Signup and view all the answers

Which term describes the way bacterial exotoxins can affect a human host through the ingestion of a preformed exotoxin?

Toxin-mediated disease Signup and view all the answers

How does Vibrio enterotoxin affect the intestinal tract?

Stimulates excessive electrolyte secretion Signup and view all the answers

What is the characteristic action of the tetanus toxin?

Blocks inhibitory neurons to skeletal muscle Signup and view all the answers

Study Notes

Introduction of Bacterial Pathogenesis

Infection is the growth and multiplication of a microbe in or on the human body, with or without the production of disease.
Disease is an abnormal state in which all or part of the body is not functioning properly.
Pathogenicity is the ability of a bacterium to cause disease.
Virulence is the measure of the pathogenicity of a microorganism.
Pathogenesis refers to both the mechanism of infection and the mechanism by which disease develops.
Virulence factors contribute to an organism's virulence
- Adhesion factors
- Biofilms
- Extracellular enzymes
- Toxins
- Antiphagocytic factors

Terms

Pathogen is a disease-causing organism.
Pathology is the scientific study of disease.
Etiology is the causative agent of a disease -- what causes the disease.
Host is the organism that shelters and supports the growth of pathogenic organisms.

Strict vs. Opportunistic Pathogens

Strict pathogens are more virulent and cause disease in a typical healthy person.
Opportunistic pathogens are usually part of the normal flora, cause diseases when introduced into an unprotected site, typically occur in people with underlying conditions.

Mechanisms of Pathogenicity

Pathogens must gain access to the host, adhere to host tissue, penetrate or evade host defenses, and cause damage to host tissue.

Portals of Entry

Mucous membranes are the easiest and most frequent route of infection.
- Respiratory tract - inhaled through the nose or oral cavity, common cold, pneumonia, influenza, etc.
- Gastrointestinal route - ingested through contaminated food or water, poliomyelitis, hepatitis A, etc.
- Genitourinary tract - contracted sexually, STI's (HIV, syphilis, etc).
Skin is a barrier to microorganisms, but some pathogens penetrate normal skin (hookworm) or grow on the keratin (ringworm).
Parenteral route refers to microorganisms deposited directly below the skin through puncture wounds, injections, bites, etc. (tetanus, rabies, hepatitis B).
Preferred portal of entry is the route of entry needed for some organisms to cause disease. Other organisms may cause disease through many different routes.

Numbers of Invading Microbes

The LD50 (lethal dose for 50% of hosts) is the amount of a toxin needed to kill 50% of a population within a given timeframe.
The ID50 (infectious dose for 50% of hosts) is the dose of bacteria required to produce a demonstrable infection in 50% of the test animals.
Disease is more likely with more organisms.

Adherence of Microorganisms

Microorganisms must adhere to host tissues after entry.
Adherence - Microorganisms after entry into host must adhere to host tissue
- Surface molecules (ligands and adhesins) bind specifically to receptors on host cells.
- Glycocalyx, pili, fimbriae, flagella
Altering the receptor, adhesin, or both alters the ability for infection to occur.

Biofilms

Biofilms are communities of microorganisms and their extracellular products that attach to surfaces (living and non-living) and are resistant to disinfectants.

Mechanisms which assist bacterial survival in the host

O antigen polysaccharide chain
Capsular antigen
Capsule production
M protein production
Production of Fc-binding proteins
Production of leukotoxins
Interference with phagosome-lysosome fusion
Resistance to oxidative damage
Antigenic mimicry of host antigens
Antigenic variation of surface antigens
Coagulase production

How pathogens penetrate host defenses

Capsules impair phagocytosis by preventing phagocytic cells from attaching to the microorganism.
Components of Cell Wall:
- M-protein mediates attachment to epithelium and resists phagocytosis, produced by Streptococcus pyogenes.
- Opa (opacity-associated) protein inhibits T helper cells, produced by Neisseria gonorrhoeae.
- Mycolic acid (waxy lipid) resists digestion, produced by Mycobacterium tuberculosis.
Enzymes:
- Coagulase converts fibrinogen to fibrin clot, isolates microorganism from host defenses, produced by Staphylococci.
- Kinases break down fibrin (Streptokinase - Streptococci; Staphylokinase - Staphylococci).
- Hyaluronidase breaks down cell-to-cell adhesions in connective tissue, produced by Streptococci.
- Collagenase breaks down collagen in connective tissue, produced by Clostridium perfringens.
- IgA proteases destroy antibodies.
Necrotizing Factor causes death (necrosis) of tissue cells.
Antigenic Variation alters surface proteins, evading the immune system.
Penetration into host cell cytoskeleton:
- Invasins rearrange actin filaments allowing the microorganism to move into a cell.

How Pathogens Damage Host Cells

Pathogens use host's nutrients, cause direct damage in the vicinity of infection, or produce toxins.

The Production of Toxins

Toxin: Substance that contributes to pathogenicity; Poisonous compound produced by microorganisms.
Toxigenicity: Ability of a microorganism to produce a toxin.
Toxemia: Presence of toxin in the host's blood.
Toxoid: Inactivated toxin used in a vaccine.
Antitoxin: Antibodies against a specific toxin.

Toxins

Toxins can cause fever, cardiovascular abnormalities, diarrhea, shock, destroy blood cells, disrupt the nervous system, etc.
There are 2 types of toxins: exotoxins and endotoxins.

Exotoxins vs. Endotoxins

Exotoxins are proteins produced inside pathogenic bacteria, secreted into surrounding medium, and can act on specific target cells.
Endotoxins are part of the outer membrane of Gram-negative bacteria and released when the bacteria die.

Exotoxins

Neurotoxins attack nerve cells.
Cardiotoxins attack cardiac cells.
Hepatotoxins attack liver cells.
Enterotoxins attack the lining of the GI tract.
Cytotoxin attacks a wide variety of cells.

Specific Exotoxins

Diphtheria toxin - Cornybacterium diphtheriae - inhibits protein synthesis in eukaryotic cells.
Erythrogenic toxin -Streptococcus pyogenes - damages plasma membranes of capillaries under the skin, causing a scarlet fever rash.
Botulinum toxin - Clostridium botulinum - prevents nerve impulse transmission by inhibiting acetylcholine release, causes flaccid paralysis.
Tetanus toxin - Clostridium tetani - blocks inhibitory neurons to skeletal muscle, causing uncontrollable muscle contractions (lock jaw).
Vibrio enterotoxin - Vibrio cholerae - causes cells to secrete large amounts of electrolytes, causing diarrhea.
Staphylococcal enterotoxin - Staphylococcus aureus - similar to cholera toxin.

Roles of Exotoxins in Disease

Bacterial exotoxins affect a human host in three main ways:
- Ingestion of preformed exotoxin
- Colonization of a mucosal surface followed by exotoxin production
- Colonization of a wound or abscess followed by local exotoxin production.

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Description

This quiz covers the fundamental concepts of bacterial pathogenesis, focusing on infection, disease, pathogenicity, and virulence. You'll learn about various virulence factors and the distinction between strict and opportunistic pathogens. Test your knowledge on the mechanisms of infection and disease development.