Host-Microbe Interactions and Pathogenesis Part 1

Microbiology (1)

define Medical Microbiology

the study of prevention, diagnosis, treatment, and mechanisms of human infectious disease

define infectious disease

body disorders caused by 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 that they produce

define host (in relation to infectious diseases)

the individual being infected by microbes

define host- microbe interactions

exchanges that happen between individual people and the microbes that grow in and on their body

beneficial interactions

every epithelial tissue on our body supports the growth of microbes

other names for normal microbiota

also called healthy bacteria/normal flora

what does the normal microbiota act as

as a shield or protective layer

describe microbial antagonism

the process used by normal microbiota that protects us

what happens in microbial antagonism?

normal microbiota adapt to the chemical and physical conditions on a body surface and they use up all the available food and living space, leaving no food for pathogenic bacteria.

normal microbiota grows and antagonizes (prevents) pathogen growth

dysbiosis

alterations in the normal microbiota that lead to disease (from changes in the body)

what can dysbiosis lead to?

opportunistic infections

clostridium difficile (c-diff)

a common cause of infection acquired from the hospital

why would patients recieving antibiotics sometimes experience dysbiosis?

because the antibiotics can disrupt or kill some of the normal microbiota growth and

the loss of some of the normal microbiota members can cause dysbiosis

what type of pathogen is c-diff?

opportunistic pathogen

growth of c-diff causes?

moderate to severe diarrheal disease that can be hard to treat

neutral interactions

when the pathogen becomes part of the normal microbiota (because

some people are able to prevent normally pathogenic microbes from growing)

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%

what percent of college students carry (in their throat microbiota) the bacteria which causes bacterial meningitis?

10-30%

explain how diaper rash (dermatitis) occurs

dysbiosis can result in the carriers becoming infected with the microbes they carry

water against the skin strips oils and electrolytes

pathogens grow more quickly when this happens

skin harbors bacteria and yeast

candida albicans

a yeast that is part of the skin, mouth, throat, vaginal tract microbiota

what leads to yeast infection?

alterations in the chemical environment promoting candida growth

harsh soaps or cleansers can raise pH and allow candida to grow

tight clothes can also trap heat and moisture and cause yeast to grow

high blood sugar in diabetics increases growth by increasing available food

What would be required from opportunistic pathogens for infection to happen?

either dysbiosis or a homeostatic imbalance in the host or BOTH

can primary pathogens cause infections in healthy hosts?

yes they can, and they do not require either dysbiosis or imbalances

Can primary pathogens cause infections anywhere in the body?

NO! they are adapted to require specific conditions for growth

What do specific growth conditions of primary pathogens lead to?

preference of a pathogen for a specific location in the body (aka a pathogen’s tropism)

tropism

where in the body a pathogen causes disease

ideal growth conditions

conditions that maximize growth rate

growth conditions that impact growth rate

availability of nutrients, vitamins, biological molecules, temperature, pH, salt concentration, oxygen availability, immune system activity

the broader the conditions that allow growth…

the broader the tropism will be

staph aureus

a generalist that can live in many environmental conditions and cause infections almost anywhere in the body

is c-diff an obligate anaerobe?

yes, and it has highly specific nutrient requirements for growth

why is c-diff’s tropism limited to the large intestine only?

because it is an obligate anaerobe and

it has highly specific nutrient requirements in order to grow

why is viral tropism different?

because all viruses infect the inside if human cells

are the chemical conditions for growth inside of cells different in each type of cell?

the chemical conditions are roughly the same in all types of cells

attachment stage

the first stage of viral replication and infection, the virus binds to a protein in the plasma membrane (this protein is called the viral receptor)

viral tropism depends on what?

where the viral receptor (the protein that the virus binds to during the attachment stage) is found on the cells in the body

where is flu virus tropism?

In the respiratory tract

flu virus receptor is a sugar called sialic acid and it can only be found where?

cells of the lungs

where is ACE 2 (receptor) found

found in most organs of the body, but is MOST abundant in the lungs and blood vessels.

what receptor does COVID use?

ACE 2

explain how it makes sense that COVID is a lung clotting disease and it can have other long term effects

because it uses a receptor called ACE 2 that is most abundant in the lungs and blood vessels

pathogenicity

the ability of a microbe to cause a disease

pathogenicity is a binary state because

a microbe either can potentially cause a disease or it can not.

define virulence, and what does it depend on?

the degree or extent to which a pathogen causes disease, it depends on both the physiology of the microbe and the physiology of the host’s interactions with it. (virulence of a pathogen can vary between individuals)

virulence is comparative which means what?

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

virulence factors

a variety of proteins and cellular structures that help them when causing infections

the more virulence factors…

the more virulence

where are flu infections most virulent?

in people who are immunosuppressed or have immature immunity

what is a microbial toxin?

harmful substances produced by microorganisms like bacteria, fungi, and viruses, which can damage host tissues and disable the immune system. They can be classified as exotoxins (actively secreted) or endotoxins (part of the bacterial outer membrane)

difference between an endotoxin and an exotoxin

Search Assist

Endotoxins are part of the outer membrane of Gram-negative bacteria and are released when the bacteria die, while exotoxins are proteins secreted by both Gram-positive and Gram-negative bacteria during their metabolic processes. Exotoxins are generally more toxic and can cause harm at lower concentrations compared to endotoxins.

three types of exotoxins and how they damage cells of the body

The three main types of exotoxins are superantigens (Type I), which activate a large number of T cells leading to an overwhelming immune response; membrane-damaging toxins (Type II), which disrupt cell membranes causing cell lysis; and A-B toxins (Type III), which interfere with cellular functions by entering cells and disrupting internal processes. Each type damages cells through specific mechanisms that can lead to severe health