Microbiology Chapter on Pathogens and Hosts

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Questions and Answers

What is the primary function of Type IV pili in bacteria?

To elongate and attach to surfaces (correct)

To inhibit host cell attachment

To facilitate interaction with other bacteria

To secrete exotoxins

Which of the following proteins binds to host cell fibronectin?

M protein (correct)

Pertactin

LPS

CD4

What determines an individual's susceptibility to pathogens?

The presence of exotoxins

The overall health of bacterial colonies

The type of bacteria present in the environment

The availability of specific host receptors (correct)

How do exotoxins affect host cells?

They kill host cells and unlock their nutrients Signup and view all the answers

Which of the following can render an individual resistant to HIV infection?

Lacking the CCR5 coreceptor Signup and view all the answers

What defines pathogenicity in an organism?

An organism's ability to cause disease, defined by infectivity and virulence Signup and view all the answers

Which of the following best describes opportunistic pathogens?

Pathogens that cause illness in compromised hosts Signup and view all the answers

What role do ectoparasites play in host-pathogen interactions?

They benefit at the host's expense while living on the host's surface Signup and view all the answers

Which transmission route involves the direct transfer of pathogens from one host to another?

Horizontal Transmission Signup and view all the answers

What is a characteristic of latent infections?

The microbes enter a dormant state Signup and view all the answers

How is virulence measured?

Using lethal dose (LD50) and infectious dose (ID50) Signup and view all the answers

Which best describes the role of reservoirs in infection cycles?

They are environments or animals that harbor the pathogen Signup and view all the answers

What distinguishes primary pathogens from opportunistic pathogens?

Primary pathogens can only infect healthy individuals Signup and view all the answers

What defines an asymptomatic carrier?

A person who can transmit a disease but has no symptoms. Signup and view all the answers

Which of the following best describes virulence factors?

Characteristics that enable pathogens to enter and multiply in hosts. Signup and view all the answers

What is the role of adhesins in microbial infection?

To promote the attachment of microorganisms to host cells. Signup and view all the answers

What distinguishes Type IV pili from Type I pili?

Type IV pili are involved in twitching motility and dynamic attachment. Signup and view all the answers

What is the primary function of pathogenicity islands?

To cluster pathogenicity genes encoding virulence functions. Signup and view all the answers

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

Asexual Signup and view all the answers

What effect do intestinal pathogens generally have on the microbiome?

They reduce the diversity of gut microbiota. Signup and view all the answers

Which molecular postulate involves the inactivation of a gene leading to loss of virulence?

Inactivation of gene leads to loss of virulence. Signup and view all the answers

What is the primary role of the A subunit in AB exotoxins?

Destroys host protein functions Signup and view all the answers

Which exotoxin leads to a significant increase in cAMP levels within host cells?

Cholera toxin Signup and view all the answers

What mechanism does anthrax toxin use to affect host cells?

Blocking immune cell recruitment Signup and view all the answers

Which of the following toxins is associated with acute kidney failure?

Shiga toxin Signup and view all the answers

What is the function of protective antigen (PA) in anthrax toxin?

Delivers A subunits into host cells Signup and view all the answers

What effect does diphtheria toxin have on protein synthesis?

ADP-ribosylates eEF-2 Signup and view all the answers

Which of the following best describes the structure of AB5 exotoxins?

Five identical B subunits arranged in a ring with one A subunit Signup and view all the answers

Which enzyme modification mechanism does ADP-ribosyltransferase enzymes employ?

Transfer of ADP-ribose from NAD to amino acids Signup and view all the answers

Which organism type produces exotoxins?

Both Gram-positive and Gram-negative bacteria Signup and view all the answers

What is the primary chemical structure of endotoxins?

Lipopolysaccharide Signup and view all the answers

Which statement regarding heating endotoxins is correct?

Endotoxins remain unchanged when boiled. Signup and view all the answers

What is the immunogenicity of exotoxins compared to endotoxins?

Exotoxins are highly antigenic, while endotoxins have poor antigenicity. Signup and view all the answers

Which of the following is a characteristic feature of exotoxins?

Can be made into toxoids for vaccinations Signup and view all the answers

Which of these toxins is specifically known for its pore-forming ability?

Alpha toxin of Staphylococcus aureus Signup and view all the answers

Endotoxins are primarily responsible for what condition in Gram-negative infections?

High fever production Signup and view all the answers

Which type of microbial exotoxin disrupts the proper function of vesicular trafficking?

Inhibitors of exocytosis Signup and view all the answers

What role do Tir proteins play in the interaction between pathogenic E.coli and host cells?

They act as receptors for the bacterial protein intimin. Signup and view all the answers

Which of the following strategies is NOT used by pathogens to avoid extracellular immune responses?

Induction of apoptosis in non-phagocytic cells. Signup and view all the answers

Which mechanism do intracellular pathogens NOT use to prevent destruction by the phagolysosome?

Induce cell division in host cells. Signup and view all the answers

What is the main function of autophagy in relation to intracellular pathogens?

Form vesicles around damaged organelles. Signup and view all the answers

How do primary pathogens differ from opportunistic pathogens?

Primary pathogens cause disease in normal hosts. Signup and view all the answers

Which type of pili is static and responsible for bacterial attachment?

Type I pili Signup and view all the answers

What is the primary purpose of molecular tricks employed by intracellular pathogens?

Mislead the immune system. Signup and view all the answers

Which of the following statements about adhesins is correct?

Type I pili provide static attachment. Signup and view all the answers

Study Notes

Microbial Pathogenesis Overview

Host-pathogen interactions are studied, including how microbes attach to host cells, how toxins affect host functions, and how toxins and effectors are deployed.

Introduction

Mammalian defenses include physical, chemical, and immunological barriers against disease-causing microbes.
Pathogenic microbes exploit weaknesses in defenses to cause disease.
How can a microorganism too small to be seen kill a human a million times larger? This fundamental question is explored in the study of host-pathogen interactions.

Host-Pathogen Interactions

Humans and their ancestors have experienced infections for millions of years.
Robert Koch discovered Bacillus anthracis causes anthrax.

The Language of Pathogenesis

Parasites benefit at the host's expense; they include bacteria, viruses, fungi, and protozoa.
Ectoparasites live on the host's surface, while endoparasites live inside the body.
Infection occurs when a pathogen or parasite grows in/on a host. Not all infections cause disease.
Primary pathogens cause disease in healthy hosts, opportunistic pathogens cause disease in compromised hosts, and latent infections involve microbes entering a dormant state.

Infection Cycles

The cycle describes the transmission route of the infectious organism.
Horizontal transmission involves direct (e.g., sneezing, touch) and indirect (e.g., fomites, food, water) contact.
Vertical transmission occurs from mother to fetus during pregnancy or birth.
Vector transmission involves arthropods carrying pathogens (e.g., mosquitoes).

Reservoirs and Portals of Entry

Reservoirs are environments or animals harboring pathogens (e.g., monkeys for yellow fever, birds for eastern equine encephalitis virus).
Asymptomatic carriers are individuals who harbor pathogens but show no symptoms.

Immunopathogenesis

Immunopathogenesis is the immune response to a pathogen that causes tissue/organ damage.
Study of both pathogenic mechanisms and immunopathogenesis symptoms are crucial.

Effect of Infections on the Microbiome

Host's normal microbiome is affected by pathogen growth and immune response.
Example: Diarrhea reduces gut microbiota; intestinal pathogens alter nutrient availability.

Virulence Factors

Requirements for disease include entering the host, finding a niche, avoiding host defenses, multiplying, and transmitting to a new host.
Virulence factors (e.g., toxins, attachment proteins, capsules) are encoded by virulence genes.
Molecular Koch's postulates describe determining pathogenic strains by inactivation of a pathogen gene and reversion allowing restoration to pathogenicity.

Pathogenicity Islands

Clusters of pathogenicity genes encoding virulence functions.
These genes can be transmitted horizontally via conjugation or transduction.
Unique GC/AT ratio, linkage to tRNA genes, association with phages/plasmids may be seen as anomalies.

Microbial Attachment

Attachment/adhesion is the initial step toward infection.
Adhesins are microbial factors that promote attachment (e.g., pili, adherence proteins, cell surface molecules).

Pili (Fimbriae)

Hair-like appendages made of pilin protein subunits.
Tips contain receptors (e.g., FimH) for attaching to host cell receptors.
Types of pili include Type I (static attachment) and Type IV (dynamic attachment via assembly/disassembly).

Assembly of Type I Pili

Protein subunits assemble like jigsaw pieces.
New subunits are added to the bottom of the structure.

Type IV Pili - Model of Pilus Assembly and Disassembly

At least a dozen proteins are involved.
Functions include pili elongation for attachment, retraction for cell movement, and disassembly.
Examples include E. coli and N. meningitidis.

Nonpilus Adhesins

These adhesins strengthen interactions between bacteria and target cells.
Examples include Streptococcus pyogenes M protein binding to host cell fibronectin.

Susceptibility to Infections

Factors include immunocompetence (the ability to resist pathogens) and receptor availability.

Host Receptors and Pathogen Susceptibility

Pathogens use specific surface structures (receptors) to recognize and attach to host cells.
Variations in receptors between individuals can affect susceptibility.

Toxins Subvert Host Functions

Exotoxins are proteins produced and secreted by various bacteria.
Exotoxins kill host cells and utilize their nutrients.
Endotoxins are part of Gram-negative bacterial lipopolysaccharide (LPS) and hyper-activate the immune system.

Producing Organisms & Exotoxins (Chemical, Denatured, Mode of Action, Enzyme Activity, Toxicity, Immunogenicity, Vaccine, Fever Production)

A table shows categories of microbial exotoxins with their chemical properties (protein or LPS),denaturation status, specific actions, and their impact (high or low) on various aspects including enzyme activity and fever production.

Two-Subunit AB Exotoxins (Structure, A Subunit, B Subunit, ADP-Ribosyltransferase Enzymes)

These toxins have an A subunit for toxicity and a B subunit for binding host cells and delivering the A subunit.
AB5 toxins contain 5 identical B subunits and 1 A subunit.
ADP ribosyltransferase enzymes modify protein structure and function. This relates specifically to the way some toxins function, that is transferring ADP-ribose groups.

Examples: Cholera Toxin, Anthrax Toxin

Cholera toxin increases cAMP levels in host cells, leading to diarrhea.
Anthrax toxin has subunits with functions causing cytotoxicity involving proteins (e.g., edema factor and lethal factor)
Shiga toxin interferes with protein synthesis.

Deployment of Toxins and Effectors (Protein secretory proteins, Type II, III, IV, Mechanism, Examples)

Bacteria use protein secretory systems to move toxins into host cells
Type III secretory system (T3SS) injects proteins into host cells. The T3SS, in this example, contains a tiny molecular syringe and allows for the transfer of proteins to aid in the infection.

Surviving Within the Host (Extracellular Immune Avoidance)

Strategies for survival include capsule production, inhibiting antibody binding, inducing apoptosis, or altering surface antigens.
Intracellular immune avoidance involves strategies to avoid phagosome-lysosome fusion, growing inside the phagolysosome, or escaping the phagosome, relying on autophagy.
Pathogens employ molecular tricks to misdirect immune responses, buy time to overwhelm the host, or use autophagy, an internal cellular process.

Immune Avoidance (Two-Subunit AB toxins, Endotoxin, Protein Secretion Pathways, Bacteria, examples, mechanisms)

Bacteria employ molecular mimicry, interfering with autophagy, and redirecting ubiquitylation signals (all methods of evading the host immune responses).

Studying That Suits You

Use AI to generate personalized quizzes and flashcards to suit your learning preferences.

Description

Test your understanding of key concepts in microbiology, focusing on pathogens, host interactions, and factors influencing infections. This quiz covers various aspects including Type IV pili, virulence, and opportunistic pathogens. Perfect for students looking to deepen their knowledge in microbial pathogenesis.