Topic I: Intro to Bacteriology

What are microbes?

Small organisms only visible w/ a microscope

• Cellular & acellular

What are the cellular microbes?

• Fungi (yeast)

• Bacteria (e. coli)

• Protists (algae, protozoa)

• Parasitic worms (flatworms, roundworms, flukes)

What are the acellular microbes?

• Viruses (made of proteins & nucleic acids)

• Prions (made of protein only)

• Viriods & virusoids (made of RNA only)

Who discovered microorganisms?

Antony van Leeuwenhoek (1632-1723)

• First person to observe & describe microorganisms accurately

• Microscope: 50-300x

• Observed bacteria & protozoa

Who discovered indirect evidence that microorganisms were casual agents of disease?

Joseph Lister (1827-1912)

• Developed antiseptic surgery techniques (~1865)

  • Heat sterilization; phenol

    • Prevent microorganisms from entering wounds

• Fewer postoperative infections

Who established relationship b/w Bacillus anthracis & anthrax?

Robert Koch (1843-1910)

• Injected healthy w/ material from sick

• Sick spleen into culture

• Spores into healthy mice

• These criterial now known as Koch’s postulates

  • Still used today to establish link b/w microorganisms & disease

What is Koch’s postulates?

To prove a casual relationship b/w microorganisms & disease

1. Microorganisms must be present in every case of disease but absent from healthy individuals

2. Suspected microorganism must be isolated & grown in a pure culture

3. Same disease must result when isolated microorganism is inoculated into a healthy host

4. Same microorganism must be isolated again from diseased host

What is Koch’s postulates applied to TB (example)?

1. Koch developed staining technique for TB in human tissue. Mycobacterium tuberculosis Could be identified in each case of TB

2. Koch grew M. tuberculosis in pure culture on coagulated blood serum

3. Koch injected cells from pure culture of M. tuberculosis into guinea pigs- they died of TB

4. Koch isolated M. tuberculosis in pure culture from dead guinea pigs

What are the limitations of Koch’s postulates?

• Some microbes are found in both sick & healthy individuals

• Microbes may not cause disease in every person

• Ex. Helicobacteria pylori → GI tract of 50% population (causes >90% of stomach ulcers)

What is the recent update w/ molecular postulates?

1. Sometimes only difference b/w pathogenic (disease-causing) & non-pathogenic bacteria is 1 gene

• Virulence gene- expresses a trait that is responsible for causing disease

2. Antibodies against virulence gene product → may lead to protection from disease

• Can be a goal of vaccine development

• Ex. “ap” in Tdap vaccine= “acellular pertussis”

Do all microbes cause disease?

Most do not, many are quite beneficial for us

What is the microbiome/“normal flora”?

You have more bacterial cells than human cells on your body rn

• Normal human body;

  • 10^13 human cells

  • 10^14 bacterial cells

  • Bacterial out number our cells 10 to 1

What are the surfaces covered in large amounts of bacteria?

• Skin

• Nose/mouth

• Gi tract

• Vagina

What are areas where bacteria are in transit, but shouldn’t colonize?

Bladder

What are areas where bacteria should NEVER be (sterile!)?

• Blood

• CSF

How can normal flora be beneficial?

Compete for space & nutrients w/ pathogenic bacteria

• Advantage of previous occupancy (“exclusionary effect”)

• Gut, vagina

  • Ex. Lactobacilli → producing lactic acid → decreases pH in vagina → prevents yeast growth

How can normal flora be pathogenic in certain locations/circumstances?

Entry unto a different tissue

• Ex. E. coli → normal flora in gut → if it enters urinary tract → UTI

• Immunocompromised patients

What is the induction of immunity w/ normal flora?

• Hygiene hypothesis

  • Immature immune system needs to be exposed to a variety of antigens to learn what’s dangerous & what’s benign

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

• Normal flora may influence susceptibility to autoimmune diseases

  • Question of bacterial numbers & diversity

  • Obesity, diabetes, irritable bowel syndrome (IBS), asthma, atrophy (hyperallergic)

  • Ex. Risk of asthma & gut bacteria in infants