Microbiology Chapter 16: Host-Microbe Interactions

Some microbes can evade immune response mechanisms by avoidance of ____ destruction. This can include interfering with any of the steps involved in the process, including chemotaxis, recognition and attachment, engulfment, and fusion of the phagosome with ___.

Phagocytic; lysosomes

What describes acute infections?

They are generally short in duration

What are mechanisms used by non-invasive pathogens to cause disease in the host?

- Production of toxins that are then ingested

- Colonization of host mucous membranes followed by toxin production

The presence of bacteria in the bloodstream.

Bacteremia

The presence of toxins circulating in the bloodstream

Toxemia

The presence of free viral particles in the blood

Viremia

Pathogens can be distinguished from other microbes by their ability to

Overcome the body's immune defense and cause damage

Which methods might a virus employ to avoid extracellular antibody binding?

Stimulation of syncytium formation (forced fusion of cells)

Moving directly from one cell to another

Exotoxins can be found in extracellular fluid after they are ___ by bacteria or after they leak into the fluid following ___ of bacterial cells.

Secreted; Lysis

Example of direct and indirect damage caused by microorganisms?

Direct - Toxins

Indirect - Immune response

Steps resulting in directed uptake of salmonella species in intestinal epithelial cells?

1. The bacteria adhere to the host cells

2. The bacteria use a type III secretion system to deliver proteins into the host cells

3. Bacterial proteins cause rearrangement of actin molecules in the host cell

4. Characteristic membrane ruffling occurs on the host cell's surface

5. The host cell's membrane encloses around the bacterial cell(s), bringing them in

If scarring from the inflammatory response damages the inner areas of the fallopain tubes of the female reproductive tract, there is a higher likelihood of

- Ectopic pregnancy (the fertilized egg implants outside the uterus)

- Sterility due to the prevention of fertilization by physical blockage of the tubes

When oral antibiotics inhibit members of the normal intestinal microbiota, what occurs?

Toxin producing Clostridium difficile may flourish without competition from other microbes leading to diarrhea and colitis.

Streptococcus pyogenes is a member of the normal microbiota in some individuals that can cause ____ throat or necrotizing fasciitis ("____ disease") depending on the virulence of the strain involved.

Strep throat

"Flesh-eating disease"

What is the chemical composition of endotoxins?

Lipopolysaccharide

What are examples of exotoxin categories based on general structure/mechanism?

Membrane damaging toxins

Superantigens

A-B toxins

Peptidoglycan can cause symptoms similar to those that characterize the response to ____. The systemic response leads to ____.

Endotoxin

Septic shock

By surviving within ___, pathogens are able to hide from antibodies, control some aspects of the immune response, and be transported to other locations in the body.

Macrophages

Examples of bacteria that are invasive pathogens include:

Mycobacterium tuberculosis

Shigella dysenteriae

Clostridium tetani

Yersinia pestis

An M cell is a specialized cell of the mucosa-associated lymphoid tissues (MALT) that samples the materials from the intestinal ___. As such, it can be ___ by pathogens to cross membranes.

Lumen; used

___ pathogens are able to penetrate the body's first line defenses and then multiply in host tissue.

Invasive

Membrane attack complexes (MAC) formation is more dangerous to gram-negative cells than to gram-positive cells. Why?

The cell wall in gram negative cells has an outer membrane, allowing for better insertion of the MAC structure through it.

What are bacterial cell wall components to which the host defenses are primed to respond?

Lipopolysaccharide

Peptidoglycan

____ are the traits of a microbe that specifically allow it to cause disease.

Virulence factors

Many pathogens enter via

Mucous membranes

What are some of the benefits of normal microbiota to our health?

They help us digest our food

They protect us against infection

They produce beneficial compounds

Infection refers to what?

A microbe establishing itself onto a body surface and into a parasitic relationship with its host

What variables may reasonably be assumed to affect the duration of the incubation period?

Age of the individual

The host's general physical condition

The number of infectious particles encountered

Growth rate of the pathogen

A ____ pathogen causes disease only when the body's innate/adaptive defenses are ____.

Opportunistic

Compromised

Pathogens must first adhere to host cells to initiate an infection for what reason?

First line defenses are very effective in sweeping away microbes

What describes the incubation period?

The time between exposure/infection by the disease-causing microbe and the onset of physical illness

Two ways in which exotoxin can enter the body or its tissues include ___ of preformed exotoxin molecules in food/water and secretion of exotoxin by pathogens following ___ of host tissues.

Ingestion

Colonization

Types of exotoxins based on tissues/cell types affected?

Neurotoxins

Cytotoxins

Enterotoxins

During which phases/stages of an illness can a person be contagious to others?

Illness

Incubation

Covalescence

Septic shock is due to

An overwhelming systemic immune response

What is the classic example of an endotoxin?

Lipopolysaccharide

T or F: Endotoxin can cause septic shock

True

If a person is suffering from an exotoxin-induced disease like tetanus, treatment with ____ (a suspension of exotoxin-neutralizing antibodies) would be helpful

Antitoxin

Infectious diseases that ___ from one host to another are called communicable, or ___ diseases.

Spread; contagious

A good example of a ___ infection would be a boil caused by S. aureus. A good example of a ___ infection would be measles, where the infectious agent is spread throughout the body.

Localized

Systemic

Match the toxin subunit with the possible beneficial use.

A - fuse it to a compound that will attach to a specific cell type that needs to be destroyed

B - fuse it to a medication

What describes resident microbiota?

They typically inhabit body sites for extended periods of time.

In the process of directed uptake, what occurs?

A host cell is tricked into engulfing a pathogen, which infects the host cell

By forcing cellular neighbors to ___ (forming syncytia), viruses can ___ extracellular antibody binding and neutralization

Fuse

Avoid

What long lived protective outcomes have been achieved/produced in an individual who has overcome an infectious disease with an immune response?

Accumulation of protective antibodies

Production of memory B cells

Production of memory T cells

The enzyme C5a ___ degrades the complement component C5a.

Peptidase

A protein that a bacterium injects into a host cell, with the result the host cell's cytoskeleton structure is altered is an example of

Effector protein

A type III secretion system, also know as an ____, is a syringe-like structure that injects bacterial proteins into ____ cells.

Injectisome

Eukaryotic

Capsules on microbes help the cells avoid recognition and attachment by phagocytes. They do this by which of the following methods?

Binding host complement regulatory proteins that inactivate C3b, preventing opsonization

Binding host complement regulatory proteins that inactivate C3b complement protein, preventing MAC formation

Adhesins are often located at the end of ___ or as a ___ of the capsule or cell wall structure in bacteria

Pili

Component

Antigenic variation as used by Neisseria gonorrhoeae occurs when what happens to the cells?

They change the structure of the pili so that specific antibodies produced can no longer bind to them

Secretory IgA is found in the secretions that coat mucus membranes, thereby preventing pathogens from colonizing mucosal surfaces. What are methods that bacteria have evolved to evade or inactivate these antibodies?

IgA proteases that cleaves the antibodies, so that they cannot bind to the pathogen

Antigenic variation (altering the bacterial structures the antibody binds to)

Rapid turnover of pili structures that have been bound by the antibody

Fc receptors produced on bacterial cells work as a microbial mechanism for evasion of phagocytosis for which of the following reasons?

They bind up antibodies by the Fc region, leaving the Fab region exposed. Host cells don't have a receptor for the Fab region to attach to

Which desribes a carrier?

An individual who is still contagious to individuals around him or her

An individual who exhibits none of the symptoms of the illness

An individual who harbors an infectious agent for a long time after infection

Lactoferrin and transferrin are used by the body to bind iron, keeping it from microbes that might otherwise colonize. Pathogenic microbes get around this limitation by doing which of the following?

Producing their own iron binding molecules known as siderophores

Stripping the iron bound to lactoferrin/transferrin molecules

Molecular mimicry as an effective means of avoidance of immune responses occurs when which of the following occurs?

A microbe makes molecules to cover its exterior that "look" like host cell molecules

Lipopolysaccharide can act on which of the following cells of the immune system?

Monocytes

B cells

Macrophages

Metagenomics

Is the analysis of DNA extracted from a given environment

Is used by programs such as The Human Microbiome Project to study normal microbiota

Allows the study of all microbiota from a given environment, even ones not yet cultured

Some diseases include a prodromal phase. Where would it fit in?

Between the incubation period and illness

What would happen if a pathogen lost the ability to bind adhesins?

It could no longer attach to a certain surface, and would likely be washed away by host defenses

Example of infection with latent phase

Herpes

Shingles

What factors might contribute to a long incubation period?

Slow growth of a pathogen, low infecting dose, time for pathogen to reach the body site where it can replicate and/or cause damage, healthy/active adult

Describe 3 mechanisms pathogens might use to survive in phagocytic cells

escape from the phagosome

prevent phagosome-lysosome fusion

survive within the lysosome

Describe how Fc receptors prevent phagocytosis

They bind the part that the innate defenses normally recognize, orienting the antibody outwards so that the Fab region, which the innate defenses have no mechanism for recognizing, faces out

What's the ID50 of the bacteria causing shigellosis vs. salmonellosis? Which bacteria is more virulent?

Shigella ID50 = 10-100

Salmonella ID50 = 10^6

Shigella is more virulent

Are capsules considered a virulence factor? Why?

Yes, they block opsonization and MACs.

Epitope =

Antigenic determinants.

Recognized by specific antigen receptor

Each antibody specifically binds to one epitope

Opsonization

IgG opsonize antigens, enhance phagocytosis.

Binds around pathogen and tags for phagocytosis