Intro to Bac. Lec 1

Gain an appreciation for the diversity of the microbial world - Recognize basic features and structures of the bacteria cell - Understand differences between Gram-negative and Gram-positive bacteria -Understand what virulence factors are

What is the size of bacteria?

• micrometer

How common is it for bacteria to actually cause disease?

• There is very few bacteria that actually cause human disease (Mostly harmless)

What are 3 domains of life? Which are prokaryotes?

• Bacteria, Archaea, Eukaryotes 

• Bacteria and Archaea are prokaryotes

Does archaea cause disease

we don’t know of any of archaea that causes bacteria

What are we missing on the diagram? 

• Missing viruses on the tree of life diagram

What is the key definition of prokaryotes

lack nucleus and complex organelles 

What is the simplest, smallest and most abundant cell on Earth

Prokaryotes

What does this diagram explain

• We think life evolved 3.5 to 4 billion years ago 

• Basically microbes have been around from much longer than humans 

How does bacteria reproduce and at what speed

• reproduces by binary fission

• at a very fast speed

What are the four phases of growth

1. Lag phase

2. Log phase (exponential)

3. Stationary phase

4. Death

Lag phase

• no cell division

• there is cell growth

• cell repair

Log phase

• exponential division

• peak metabolic activity

• reaches max population

Stationary phase

• population growth flattens out

• nutrients deplete

Death phase

• nutrients exhaust

T or F: All species grow at the same speed

FALSE

• some grow fast some grow slow

In what shapes are bacteria classified in?

Coccus — sphere like shape

Rod shape — rod shape

Spirillum — spiral shape

What are the 5 ways bacteria utilizes O2

• Obligate aerobe — Need o2 to live 

• Obligate anaerobe — O2 is toxic for growth 

• Facultative anaerobe — Use 02 but dont need 

• Aerotolerant anaerobe — Dont use O2 but its not toxic 

• Microaerophile — Grow best in low o2 levels 

What slide show two e.coli

• Sequence of genome of these might only be 60% identical between the both 

• So 40% is different 

What is a gram strain

a rapid laboratory test that checks for bacteria or fungi in samples

What happens to the gram bacteria after the test

• if bacteria is gram negative, the purple washes out and become clear 

• If not positive, purple will not wash out 

Why does gram bacteria stain differently

• gram + bacteria has thick layer of peptidoglycan 

• So the thickness of the cell wall results in how they dye sticks 

Which gram has an outer membrane? What is the outer-membrane called?

Gram negative

• liposaccharides

What is another name for bacterial cell wall

• called peptidoglycan

What is bacterial cell wall made of and its purpose?

• rigid structure

• prevents osmotic lysis

What linkages go between acetylglucosamine? What does it do?

• Peptide linkages

• holds the bacterial cell wall together  

What is the naming convention for bacteria?

[Genus] [Species] [Strain]

• genus is always capitalized

• species in not capitalized

• both are italicized

What are the three components of the lipopolysaccharide

What is the O antigen and its function?

• Outermost chain that makes up lipolysacc.

• primary shield

Why is the O antigen antigenic?

antigen = substance that causes the immune system to produce antibodies against it

O antigen is a prime target for the immune system

Why is the O antigen highly variable?

Within a single species like E. coli, there are over 180 different O antigen types (serotypes)

Where is the lipid A located? What is the role of the lipid A (what is it recognized by)?

• sticks into membrane 

• Lipid A is recognized by the innate immune system which is why its important 

• Recognizes lipid A by TLR 4 and initiates immune system 

What happens if we detect too much lipid A

body can go into septic bunch

Describe the nucleoid

Not the nucleus

No surrounding membrane

Single, circular chromosome

Haploid genome

Why is MOST bacteria a singular circular molecule

an advantage for bacteria b/c it can mutate its genes faster 

Describe plasmids

Extrachromosomal DNA (Physically separate from the main bacterial chromosome)

Not required for bacterial growth

Encode for “fitness” factors

Can be transferred from bacteria to bacteria

Are our internal organs colonized by microbes?

No. Internal organs are usually sterile.

Which tissues have extensive microbial populations?

"Surface" tissues, such as skin, mouth, nose and the GI and reproductive tracts.

How does the microbiota's collective genome compare to the human genome?

It easily contains ≥100 times as many genes.

Is the microbial composition the same at every body site?

Different body sites have different microbiomes

Commensalism def

(host-microbe relationship)

one benefits without hurting the other

Mutualism def

(host-microbe relationship)

both benefit

Parasitism def

(host-microbe relationship)

One benefits (usually microbe) at expense of the other (usually host)

What are the four things that make a bacterial pathogen successful?

Colonization, invasion/toxicity, immune evasion, transmission.

What is a virulence factor?

A molecule produced by the pathogen that contributes to disease.

Does every bacterial pathogen do all four steps?

No. A good pathogen can do all four, but not all bacteria do.

What are the two groups of virulence factors?

Surface and Secreted

List the five surface virulence factors

LPS (endotoxin)

Flagella

Pili and adhesins

Capsules

Secretion systems

What is the secreted virulence factor

Exotoxins

What are flagella used for?

They allow some bacteria to be motile.

Do all bacteria have flagella?

No. Only some bacteria do

What is chemotaxis?

Directed bacterial movement in response to chemicals in the environment (moving toward an attractant).

Which direction of flagellar rotation produces a run?

Counterclockwise.

Which direction of flagellar rotation produces a tumble?

Clockwise.

How does bacterial movement look when no attractant is present?

Random movement.

What are pili?

Surface structures that allow bacteria to attach.

What three things can pili attach to?

Surfaces, host tissue, and other bacteria.

What are capsules usually made of?

(Exo)polysaccharides (sugars).

Where are capsules located?

On the outside of the bacterium, as part of the cell envelope.

What three functions of capsules are listed on the slide?

Attachment to host tissues

protection from the host immune system

formation of biofilms.

Can capsules be used in vaccines?

Sometimes, in some cases.

What is a biofilm?

A community of bacteria attached to a surface and surrounded by a slimy protective matrix that they produce themselves.

What are the four biofilm stages listed on the slide?

Attachment

microcolony development

biofilm development

maturation.

What is the key takeaway about how bacteria grow?

Bacteria grow in colonies, not alone.

What is an endospore?

A highly differentiated, dormant cell formed within the parent cell.

Which bacteria can form endospores?

Only some Gram-positive bacteria

What are endospores resistant to?

Heat, harsh chemicals and radiation.

Why are endospores described as "dormant"?

They are an inactive stage of the bacterial life cycle.

Why do we autoclave?

Because of endospores, which don't die easily.

What are exotoxins?

Toxins secreted from bacteria.

List the 4 types of exotoxins

Hemolysins

toxins that function inside host cells

extracellular enzymes

superantigens

Can exotoxins be used in vaccines?

Yes, some (inactivated) exotoxins can be used as vaccines.

What do superantigens do?

They falsely activate T cells

What is an intracellular pathogen?

A bacterium that can live inside host cells.

Do all bacteria live inside cells?

No. Only some bacteria are intracellular pathogens.

What happens to intracellular bacteria taken up by phagocytic cells?

They survive within the cells instead of being destroyed.

How do some bacteria get into epithelial cells?

They "force" their own uptake.

Why is living inside cells an advantage for bacteria?

It lets them hide from different components of the immune system.

Why are antibodies less effective against intracellular bacteria?

Antibodies mostly act outside cells, so bacteria hidden inside are out of reach