Chapter 6: Microbial Growth

Micro baddies

Describe how bacterial infections are diagnosed

- identify if bacteria belongs in a certain setting
- clinical samples are taken (throat swab, urine sample etc.)

clinical samples incubated and assessed for growth of bacteria
- there is no culture without growth; it is a culture assay unless it is positive

What bodily fluids/tissues are examples of where clinical samples can be taken from?

- blood
-cerebral spinal fluid
- urine
- throat swab
- saliva

Describe how bacterial species are determined/identified

- gram staining can be done
- identifying glucose v. other structures
- oxygen requirements
- physiological enzymes
- hemolytic activity

Define colony

A population of cells arising from a single cell or spore or from a group of attached cells

Describe how pure cultures can be isolated using the streak plate method

It progressively dilutes a mixed microbial sample across a sterile agar plate using a sterile inoculating loop in a series of streaks
-the more the loop is dragged the more isolated the organisms will be
-enough spacing is achieved after a few passes for individual, isolated colonies after incubation

Define bacterial growth, including binary fission

Bacterial growth is the reproduction of bacteria by splitting in two
- bacterial growth is the increase of number of cells, not size
-binary fission divides one cell into 2 identical daughter cells

What is binary fission

A form of asexual reproduction in single-celled organisms where one cell divides into 2 identical daughter cells

1) cell elongates and DNA is replicated
2) cell wall and plasma membrane begin to constrict
3) cross-wall forms, completely separating the two DNA copies
4) cells separate = 2 identical daughter cells

Compare the phases of microbial growth, and describe their relation to generation time

Generation time is DIRECTLY RELATED TO LOG PHASE
- represents the time for a population to double under ideal conditions

- Generation time is not yet established in lag phase
- In stationary & death stages generation time is not relevant (decrease/stabilization in population size)

What are the four direct methods of measuring cell growth?

1. Plate counts
2. Serial dilutions
3. Filtration
4. Direct microscopic count

Differentiate direct and indirect methods of measuring cell growth

Direct- counts cells individually, providing exact number but not distinguishing between dead or alive cells

Indirect- measures characteristics (cloudiness, metabolic activity, etc.) to estimate cell population size

Explain three indirect methods of measuring cell growth

1. Turbidity
2. Metabolic activity
3. Dry weight

Classify microbes into five groups on the basis of preferred temperature range

Psychrophiles: -10 - 18degrees C
Pscyhrotrophs: 0 - 31 degrees C
Mesophiles: 10 - 48 degrees C
Thermophiles: 40 - 72 degrees C
Hyperthermophiles: 67 - 110 degrees C

Identify how and why the pH of culture media is controlled

- pH of culture media is controlled
- buffers like sodium bicarbonate are added to the media to neutralize acids or bases during growth
- done to maintain optimal pH

Explain the importance of osmotic pressure to microbial growth

-if concentration of solutes is higher in surrounding medium, water leaves the cell
-inhibiting cell growth

Name a use for each of the four elements (carbon, nitrogen, sulfur, and phosphorus) needed in large amounts for microbial growth

Carbon- autotrophs use CO2
Nitrogen- in amino acids and proteins
Sulfur- used in protein decomposition
Phosphorous- in DNA, RNA, ATP, and membranes

Explain how microbes are classified on the basis of oxygen requirements

Identify ways in which aerobes avoid damage by toxic forms of oxygen

Use superoxide dismutase (SOD)
- converts superoxide into oxygen and hydrogen peroxide

Also use catalase or peroxides
-break down hydrogen peroxide into water and oxygen

Describe the formation of biofilms and their potential for causing infection

- bacteria attracted by chemicals (form slime or hydrogels)
- share nutrients
-shelter bacteria from antibiotics and immune system

What is a chemically defined medium?

A medium whose exact chemical composition is known

What is a complex medium?

A medium made up of nutrients including extracts from yeast, meat, plants, or digest of proteins
-varying chemical composition from batch to batch

Justify the use of enrichment medium

- selectively increases the population of specific microbial group in a culture
- provides nutrients and conditions to promote growth while limiting growth of other organisms
- useful for rare or slow growing bacteria

Justify the use of selective media

Selective: contains substances inhibiting growth of some organisms while allowing others to flourish
- isolates organisms from a mixed population

Justify the use of differential media

Differential: allows for visual differentiation of different colonies based on metabolic properties

Justify the use of candle jars

- burning a candle in a sealed jar
- consumes oxygen and increases CO2 levels
-allows for growth of bacteria that require low oxygen concentration

Justify the use of living host cells

viruses require a host to survive
- allows for observation of the replication process
- helps to understand virus interaction with host

Justify the use of anaerobic techniques

-environment with little to no oxygen
-allow for study of anaerobic organisms that would otherwise die

Differentiate biosafety levels 1, 2, 3, and 4

1. no special precautions
2. lab coat, gloves, eye protection
3. biosafety cabinets to prevent airborne transmission
4. sealed, negative pressure (exhaust air filtered twice)