O'Donnell Intro to Microbiology

Microbe

Small organism visible only with a microscope

What are the two types of microbes?

Cellular

• Ex. Fungi, Bacteria, Protists, Parasitic Worms

Accellular

• Ex. Viruses, Prions, Viriods, Virusoids

Which acellular microbes are made of protein only?

Prions

Which acellular microbes are made of RNA only?

Virioids and virusoids

What are Koch’s Postulates used for?

Used to establish link between a microorganism and a disease

What are Koch’s Postulates?

1. Microbe must be present in every case of disease

2. Suspected microbe must be isolated and grown in pure culture

3. Same disease must result when the isolated microbe is inoculated into a new host

4. Same microbe must be isolated again from the sick host

What are the main limitations of Koch’s Postulates?

Some microbes are found in both sick and healthy individuals, so the microbe may not cause disease in every person

What does Helicobacter pylori cause?

Almost all stomach ulcers

Can also cause gastric cancer

What molecular “updates” have been discovered for Koch’s postulates?

Sometimes, the only difference between a pathogenic and non-pathogenic strain of bacteria is one gene (virulence gene)

Antibodies against virulence gene product may be enough to protect from disease

• Can be a goal of vaccine development

Do all microbes cause disease?

Most do not, many are beneficial for us

How does the microbiome benefit the immune system?

Teaches the immune system how much to react

• Sweet spot betwen overactive and underactive

How does the number of bacterial cells compare to the number of human cells in the body?

Bacterial cells outnumber human cells approximately 10 to 1

What surfaces in the body are covered in large amounts of bacteria?

Skin

Nose/oropharynx

Mouth

GI tract

Vagina

Where in the body are bacteria in transit but should not colonize?

Bladder

• Colonization → UTI

Where in the body should bacteria never be found?

Blood and Cerebrospinal Fluid (CSF)

• If bacteria are found here, it is life threatening and requires aggressive treatment

In what ways are normal flora beneficial?

Compete for space and nutrients with pathogenic bacteria

• Advantage of previous occupancy (Exclusionary Effect)

  • Gut, vagina

  • Ex. Lactobacilli - normal flora in vaginal tract → produce lactic acid → lowers pH → prevents growth of yeast

Synthesize vitamins (Vitamin K, B12) and remove toxins (nitrosamine)

How can normal flora be pathogenic?

Entry into different tissue

• Ex. E. coli is a normal part of gut flora

  • If it enters urinary tract → UTI

Immunocompromised patients

The Hygeine Hypothesis

The immature immune system needs to be exposed to a variety of antigens in order to learn what’s dangerous and what’s benign

Extremely clean environments may not provide enough “education” (germs) to develop the immune system

Numbers and diversity of normal flora may influence susceptibility to _____

Autoimmune diseases