4.1 Host-Microbe Interactions Part 1

What are infectious diseases?

Body disorders that are caused by the harmful agents that can be transmitted from one organism to another

What are infectious diseases caused by?

Either the growth of microbes or the biological molecules they produce.

Host

The individual being infected by microbes.

Host-microbe interactions

The exchanges that occur between individual people and the microbes that grow in and on their body.

Host-microbe interactions have a range of outcomes, from ____ to ____ to ____?

beneficial, neutral, disease-causing

Normal microbiota

Non-pathogenic microbes that grow on every epithelial tissue on our body and act like a biological barrier that slows the growth of pathogenic organisms.

What is the process that normal micrpbiota use to protect us?

Microbial antagonism; they use up all of the available space and food for pathogenic bacteria.

Dysbiosis

Alterations or "imbalances" in the normal microbiota that lead to disease; caused by changes in the body.

Dysbiosis may allow for ____?

Opportunistic infections

What does it mean that C-diff is a cause of hospital acquired infection?

Antibiotic treatment in the hospital can disrupt the growth or kill some of the normal microbiota and cause dysbiosis that allows opportunistic pathogens like C-diff to grow and cause infection.

What does growth of C-diff cause?

Moderate to severe diarrheal disease that can be difficult to treat.

Beneficial interactions

Host-microbe interactions involving normal microbiota that prevent harmful pathogens from growing and causing infection.

Neutral interactions

Host-microbe interactions where normally harmful pathogens become part of the normal microbiota and do not cause infection in the host, but can be passed to others.

Carriers

People who have pathogenic microbes as part of their normal microbiota.

How much of the population carries Staph aureus in their nasal microbiota?

20-40%

How many college students carry the bacteria that causes bacterial meningitis in their throat?

10-30%

What might happen to carriers if dysbiosis occurs?

They can become infected with the microbes they carry.

How might normally neutral skin bacteria or yeast cause diaper rash?

Water kept against the skin strips oils and electrolytes causing alterations in skin chemistry and helps pathogens grow more quickly.

Candida albicans

Yeast that is part of the normal microbiota of the skin, mouth, throat, and vaginal tract.

What alterations in the chemical environment might promote Canida growth and lead to yeast infection?

Harsh soaps, tight/synthetic clothing, antibiotics, and high blood sugar.

How can harsh soaps and cleaners promote candida growth?

They can raise pH allow candida to grow

How can tight/synthetic clothes promote candida growth?

They can trap moisture and heat which increases growth.

How can antibiotics promote candida growth?

They can disrupt microbial antagonism.

Why are diabetics at more risk for yeast infections (oral thrush)?

High blood sugar increases microbial growth by increasing available food.

All opportunistic pathogens require what to cause infection?

Either dysbiosis or a homeostatic imbalance in the host.

Primary pathogens

Pathogens that can cause infections in healthy hosts and do not require either dysbiosis or imbalances as long as their specific growth requirements are available.

Tropism

The preference of a pathogen for a specific location in the body based on their conditions for growth.

What are ideal growth conditions?

The chemical and physical needs of a cell that maximize their growth rate.

Growth conditions that impact growth rate?

Availability of nutrients, vitamins, and other biological molecules; Temperature; pH; Salt concentrations; Oxygen availability; Activity of the immune system

Generally speaking, the boadder the conditions that allow growth, the ____ that organisms tropism will be.

Broader

What is the difference between the tropisms of C-diff and Staph aureus?

Staph aureus is a generalist and C-diff is an obligate anaerobe.

Generalist

Pathogen that can live in a wide variety of environmental conditions and can cause infection almost anywhere in the body.

Obligate anaerobe

Pathogen with highly specific requirements for growth that are limited to areas with no oxygen.

Why is viral tropism unique?

It depends on where the viral receptor protein is in the cell membrane.

Flu virus tropism

Respiratory tract; receptor is a sugar called sialic acid that is only found on the lung cells.

What receptor does COVID use to enter human cells?

ACE2

Where is ACE2 most abundant in the human body?

In the lungs and blood vessels

Why is COVID primarily considered a lung disease?

Because ACE2 is most abundant in the lungs

Pathogenicity

The ability of a microbe to cause a disease.

Why is pathogenicity considered a binary state?

A microbe either can potentially cause a disease or it can't.

Virulence

The degree or extent to which a pthogen causes disease.

What does it mean that virulence is typically comparative?

We compare different microbes to each other or different versions of the same microbe to each other.

Virulence depends on what?

Both the physiology of the microbe and the physiology of the host's interactions with it.

Virulence factors

A variety of proteins and cellular structures make by pathogenic microbes that aid them in causing infections.

Virulence of a pathogen is correlated to what?

The diversity and total amount of virulence factos it produces.

More virulence factors, the ______ the virulence?

Greater