Bacterial Morphology and Growth

• Bacteria morphology and growth is covered

What is a Bacterium?

• Bacteria is the plural form of bacterium
• Bacteria are microscopic, single-celled (unicellular) organisms

Bacteria Size and Shape

• Unit of measurement is the micron or micrometer (µm)
• 1 µm = 10^-3 mm
• Bacteria size varies with the kind of bacteria, age, and external environment
• Cocci are spherical and are 1µm in diameter
• Bacilli (rods) are 0.5-1 µm in width and 3 µm in length
• Spiral bacteria are 1-3 µm in length and 0.3-0.6 µm in width.

Typical Shapes

• Most bacteria maintain a specific shape.
• Some bacteria are pleomorphic, meaning they can alter their shape

Bacterial Reproduction

• Prokaryotic cell division occurs through Binary Fission (transverse)
• A single DNA molecule replicates
• Each copy attaches to a different part of the cell membrane
• The cell starts to pull apart
• Cytokinesis results in two cells of identical genetic composition

Stages of Binary Fission

• Division
• Maturation

Division Patterns

• Cell division in one plane results in chains
• Cell division in two or more perpendicular planes results in packets
• Cell division in several random planes results in clusters

Arrangements of Cocci

• Singular coccus
• Cocci in pairs results in diplococcus
• Cocci in chains results in streptococci.
• Cocci in groups of four results in a tetrad arrangement
• Cocci in clusters results in staphylococci.
• Cocci arranged in groups of eight results in sarcina

Arrangements of Bacilli

• Coccobacillus
• Bacilli
• Diplobacilli
• Streptobacilli
• Palisade arrangement

Examples of Arrangements

• Bacillus anthracis forms chains
• Corynebacterium diphtheriae forms palisades

Types of Curved Bacteria

• Vibrio cholerae
• Campylobacter
• Spirilla
• Borrelia burgdorferi

Bacterial Growth

• Microbial growth occurs at two levels: cellular and population
• Growth at a cellular level is increase in size
• Growth at a population level is increase in number of cells

Population Growth Rate

• Generation time, or doubling time, measures the time for a complete fission cycle
• Each new fission cycle increases the population by a factor of 2 through exponential or logarithmic growth
• Generation times range from minutes to days

Population Size Equation

• Nf = (Ni​)2^n is used for calculating population size over time
  • Nf​ is the total number of cells in the population
  • Ni​ is the starting number of cells
  • n denotes the number of generations

Stages of Normal Growth Curve in Laboratory Studies

• Lag phase is a "flat" period of adjustment and little growth
• Exponential growth phase means maximum growth continues with adequate nutrients and a favorable environment.
• Stationary phase is when the rate of cell growth equals the rate of cell death due to depleted nutrients and O2, and excretion of organic acids/pollutants.
• Death phase is when limiting factors intensify and cells die exponentially.

Measuring Microbial Numbers Includes

• Indirect Measurements : Turbidity and Metabolic Activity
  • Metabolic activity can be measured through formation rate of metabolic products, substrate utilization rate, or reduction rate of certain dyes
• Direct Measurements
  • Direct Count measures cells per cumm
  • Plate count measures CFU/ml
  • Filtration counts viable cells

Methods of Analyzing Population Growth

• Turbidometry is simple and measures relative population size through degree of cloudiness or turbidity.
• Enumeration of bacteria involves viable colony count or direct cell count (automated or manual)

Bacterial Colonies

• A colony is formed by bacteria growing on solid media and undergoing 20-30 cell divisions
• Each bacterial colony is a clone of cells derived from a single parent cell

Growth Factors

• Microbes can exist in many environments as they are small and easily dispersed
• Microbes require small quantities of nutrients and have diverse nutritional needs
• Environmental factors that impact bacterial growth include pH, temperature, and moisture

Growth Factors: Physical Factors

• pH, temperature, moisture, pressure, and oxygen

pH Levels

• Acidophiles thrive in acidic environments with a pH of 1 to 5.4
  • Example organisms are Lactobacillus, Acetobacter, and Gluconobacter
• Neutrophiles prefer a neutral pH range of 5.4 to 8.5
  • This range suits most bacteria causing human disease
  • Example organisms are E. coli and Salmonella
• Alkalophiles thrive in alkaline conditions,pH 8.5 to 11.5
  • Vibrio cholerae is an example organism

Temperature Preferences

• Psychrophiles/Cryophiles thrive in cold environments from 0°C to 15°C
  • Bacillus psychrophilus is an example
  • Psychrotrophs include the organisms Listeria monocytogenes and Pseudomonas fluorescens
• Mesophiles grow best at 20°C to 40°C
  • Most human pathogens fall into this category
• Thermophiles require heat to grow at 50°C to 60°C
  • These organisms are found in compost heaps & boiling hot springs
  • Examples include Bacillus stearothermophilus and Thermus aquaticus
• Hyperthermophiles exist at extreme temperatures from 80°C to 113°C
  • Sulfolobus, Pyrococcus, and Pyrodictium are examples

Extremophiles

• Able to live in unusual conditions such as absence O2, increase temperature and below earth´s surface.
  • ex: Bacillus infernus

Thermal Death Point

• The lowest temperature required to kill an organism at constant temperature.

Thermal Death Time

 - The lowest minimum temperature required to kill organism in a constant temperature.

Cardinal Temperatures

• Minimum temperature allows microbial growth and metabolism
• Maximum temperature is the highest temperature that permits microbial growth and metabolism
• Optimum temperature promotes the fastest rate of growth and metabolism.

Moisture Content

• Moisture is important for bacterial growth and is measured by Aw, which should be 0.85 to 0.95
• Only spores of spore-forming bacteria can exist in dormancy when dry
• Osmotolerant organisms do not require high solute concentrations, but can tolerate it
• Xerophiles can grow in extremely dry environments

Salt Concentration

• Halophiles are salt-loving and thrive in high salt concentrations through increased NaCl
• Example organisms are Staphylococci (7.5%) and Halobacterium

Pressure Requirements

• Barophiles grow rapidly in the presence of high pressure between 600 to 1100 atm
  • Examples are Photobacterium, Shewanella, and Colwellia

Carbon Dioxide Requirements

• Capnophiles need high CO2 concentrations
• Normally 0.3% CO2 is needed by pathogenic bacteria
• They require 5 – 10% CO2 and 15% O2
  • Hemophilus influenzae, Neisseria gonorrheae, Streptococcus pneumoniae are examples

Oxygen Requirements

• Aerobes need 21% O2 and 0.03% CO2
  • Obligate aerobes strictly need O2 to survive
    • Ex. Bordetella, Pseudomonas
  • Microaerophiles survive in reduced O2 from 2-10%, and 8-10% CO2
    • Ex. Campylobacter, T. pallidum
  • Facultative anaerobes can survive in low or absent O2
    • Ex. E. coli
• Anaerobes
• Obligate die if O2 is present and lack peroxidases
• Clostridium, Bacteroides are examples
• Aerotolerant do not die in the presence of O2 and grow well with or without oxygen via peroxidases
• S. pyogenes, E. faecalis, Lactobacillus are examples
• Facultative grow better with O2

Thioglycollate Broth

• This broth can identify a culture's oxygen requirements by the location of growth
• From left to right, the cultures are: aerobes, microaerophiles, facultative anaerobes, and obligate anaerobes

Nutritional Requirements

• Carbon source
• Energy source
• Electron source

Carbon Source

• Autotrophs: use carbon dioxide as sole source of carbon
• Heterotrophs use reduced preformed organic molecules from other bacteria ex. Glucose

Energy Source

• Phototrophs use light; absorb sunlight to produce ATP.
• Chemotrophs use energy produced by the oxidation of organic/inorganic compounds

Electron Source

• Lithotrophs get their energy from reduced inorganic molecules
• Organotrophs require organic substances, such as CHO, CHON, and lipids, for growth and multiplication Ex: all bacteria inhabiting the human body

Nutritional Terms

• Saprophytes require dead organic substances.
• Parasites require organic substances from living tissues.

Nutritional Groups

• Photoautotrophs use light energy, and get carbon from CO2
• Photoheterotrophs use light energy, and get carbon from organic compounds
• Chemoautotrophs use energy from chemical compounds, and get carbon from CO2
• Chemoheterotrophs use energy from chemical compounds, and get carbon from organic compounds