Friday July 5th

What process do bacteria us to exponentially grow under optimal conditions?

Binary Fission

For each generation of bacteria, how many times do bacteria grow?

double in size

Describe the Process of Binary Fission

• Asexual Reproduction

• Step 1: Duplicate DNA

• Step 2: Cytokines and each new organism gets one copy of DNA

Generation Time

Average time for bacterial population to double

lower generation time = faster growth rate

*cold slows bacterial growth

What is a Semilog Scale

• easier to graph bacterial growth

Explain the growth curve using the semilog scale

• lag phase: adaption to the environment

• log phase: exponential growth, cell population doubles every generation time

• stationary phase: waste accumulation, nutrients are gradually used up, cells growing and dying at the same rate

• death: toxic waste abundancy, nutrients depleted

How do you measure the number of bacterial cells?

• Serial Dilution (#’s more manageable): diluting bacteria with liquid media and plate diluted cells on an agar plate

• Used Colony-Forming Unit (CFU) Count: count bacterial colonies from a diluted bacterial sample, then calculate number of bacterial cells in the original sample

How does serial dilution work?

• taking 1ml from original solution = 1:10 dilution

• taking 2 ml from original solution = 1: 100 dilution (1:10 × 1:10)

Spectrophometer

• measure bacterial density using the property of light

• the more cloudy a tube is the more cell growth there is

• indirect method of measuring bacteria

• as cells grow, the culture becomes more turbid (cloudy), measures absorbance (optical density)

• can NOT differentiate between living or dead bacteria

How does a spectrometer work?

Sample without bacterial cells (Sample Clear)

• incoming light → cell sample → outgoing light linear

Sample with bacterial cells

• incoming light → cell sample → light scattering and detector will get less light

Understanding Absorbance: If the ingoing light intensity is = to the outgoing light intensity?

Absorbance = 0

Understanding Absorbance: If the ingoing light intensity is more than the outgoing light intensity?

Absorbance greater than 0

Understanding Absorbance: If the ingoing light intensity is much more than the outgoing light intensity?

Absorbance is much greater than 0

What is absorbance and density relationship?

higher absorbance = higher density

How do you calculate absorbance?

Beers Law

What are bacterial biofilms?

• collective of microorganisms in which cells stick together and often to a surface

• composed of extracellular polymeric substances (EPS) - mix of polysaccharides, proteins, lipids and dna

• Difficult to remove and penetrate

Name the steps for biofilm formation?

• Step 1: Planktonic (free floating) attach to the surface- eventually get tired and attach themselves to a surface

• Step 2: formation of a monolayer and production of matrix

• Step 3: Microcolony formation (multiple layer)

• Step 4: Biofilm matures, formed of polysaccharides

• Step 5: detachment and reversion to planktonic growth→ new cycle starts

Why is it difficult to remove biofilms with antibiotics?

• biofilms have a slimy texture which make it difficult to reach cells deep inside the biofilms →incomplete killing of bacteria

• antibiotics only kill the top layer of biofilms

• leftover cells from the biofilms can regenerate and form new biofilms

How do biofilms form on medical implants?

• implants can be contaminated by the microorganisms (planktonic) which can lead to colonies of bacteria that spread to other parts of the body, usually older individuals do not have a strong immune system→illness

• biofilms form on the body from implants and single cells can potentially infect the rest of the body by using the blood circulatory system

How do biofilms cause urinary tract infections?

• Biofilms form in the bladder

• Free floating bacteria turn into bacterial biofilm

• re-occuring cycle of infection - antibiotics - infection not cleared → symptoms reappear after a few days

What are the oxygen requirements for bacterial growth?

• obligate aerobes

• obligate anaerobe

• facultative anaerobes

• aerotolerant anaerobes

obligate aerobes

• need oxygen to grow

• killed by lack of oxygen

obligate anaerobe

• bacteria killed by oxygen

faculatative anaerobes

• Can do both but prefer oxygen

• grow best with oxygen, grow slower without oxygen

aerotolerant anaerobes

• grow regardless of oxygen presence or absence

What is the effect of pH in microbrial growth?

• Acidophile: grow best in acidic environments with low pH

• Neutrophile: grow best in neutral environments

• Alkaliphile: grow best in basic environments with high pH

Name the different types of growth media?

• defined media

• complex media

• selective media

• differential media

• enriched media

selective media

• inhibits the growth of a group of organisms

• bile salts interfere with the growth of many gram positive bacteria and favor the growth of gram negative bacteria

differential media

• distinguishes different types of organisms on a single plate

• crystal violet differentiates two types of bacteria

enriched media

• promotes the growth of bacteria that are normally hard to grow in lab

• ex: lysed blood cells are added to promote bacterial growth in chocolate agar

defined media

• exact chemical composition is known

complex media

• one or more compositions are known

• often contains yeast, meat, plants extract

• Contains many nutrients that may support the growth of many organism