INTRODUCTION OF BACTERIA

            Introduction to Bacteria (Bacteriology)

 Shapes of Bacteria:

 Cocci

 Chain = Streptococcus                             

 Cluster = Staphylococcus

 Bacilli

 Chain = Streptobacillus

 Coccobacillus

 Vibrio = curved

 Spirillum

 Spirochete

 Square

 Star

 Bacterial Cell Structures

Flagella:

 Motility - movement

 Arrangement basis for classification

 Monotrichous: 1 flagella

 Lophotrichous: tuft at one end

 Amphitrichous: both ends

 Peritrichous: all around bacteria

Flagella Arrangement 

 Flagella 

 Pili

Capsule

Plasma Membrane

Cytoplasm

Cell Wall

Lipopolysaccharides

Teichoic Acids

Inclusions

Spores

 Bacterial Growth

Culture: Increase in the population of cells

Generation time: The time cell takes to divide (double) is called

Reproduction: Binary Fission

 Division exactly in half

 Most common means of bacterial reproduction

 Forming two equal size progeny

 Genetically identical offspring

 Cells divide in a geometric progression doubling cell number

Binary Fission: Doubling time is the unit of measurement of microbial growth

 Bacterial Culture Growth

Growth of culture goes through four phases with time:

1. Lag phase:

• Organisms are adapting to the environment

• Synthesizing DNA, ribosomes and enzymes in order to breakdown nutrients, and to be used for growth

• Little or no division

2. Log or Logarithmic phase

• Division is at a constant rate

3. Stationary phase:

• Dying and dividing organisms are at an equilibrium

• Death is due to reduced nutrients, pH changes, toxic waste and reduced oxygen

• Cells are smaller and have fewer ribosomes

4. Death or Decline phase

• The population is dying in a geometric fashion so there are more deaths than new cells

• Deaths are due to sever reduced nutrients, pH changes, toxic waste and reduced oxygen

Bacterial Growth Curve

 Factors Influencing Bacterial Growth

Nutrition, Temperature, Oxygen, Salinity, pH, Pressure, Radiation

Nutrition:

Source of Energy:

• Bacteria are found in almost every environment because they can use widely different energy sources.

• Based on their energy source bacteria can be grouped into 4 major types

– Photosynthetic Bacteria: (1) Photoautotrophs and (2) Photoheterotrophs

– Chemosynthetic Bacteria: (3) Chemoautotrophs and (4) Chemoheterotrophs

Basic bacterial requirements:

Water: Used to dissolve materials to be transported across the cytoplasmic membrane

Carbon: required for the construction of all organic molecules

• Autotrophs use inorganic carbon (CO2) as their carbon source

• Heterotrophs: use organic carbon

Nitrogen: Obtained from:

• Inorganic source: e.g. Nitrogen gas (N2), Nitrate (NO3), Nitrite(NO2), and Ammonia (NH3)

• Organic source: e.g. Proteins, broken down to amino acids

• Many organisms use nitrogen gas by nitrogen fixation to produce ammonia

Other nutrients: Required in small amounts such as Iron, Sulfur, and Phosphorus

Nutritional Patterns:

Bacterial Temperature Requirements

Psychrophiles: Some exist below 0 ºC if liquid water is available eg. Oceans, refrigerators, and freezers

Mesophiles: Most human flora and pathogens.

Thermophiles: Hot springs, effluents from Laundromat, and deep ocean thermal vents

OXYGEN

• Required for aerobic respiration and energy production

• Organisms are classified according to their gaseous requirements

1. Obligate aerobes

2. Facultative anaerobes

3. Obligate anaerobes

Salinity

Halophiles: Bacteria that specifically require NaCl for growth

Moderates Halophiles:

• Grow best at 3% NaCl solution

• Many ocean dwelling bacteria

Extreme Halophiles:

• Grow well at NaCl concentrations of greater than 15% e.g salt lakes, pickle barrels

Halophiles growing within salt lakes often turn the water pink

Bacterial pH Requirements

Microbes have different optimum pH requirements:

Acidophiles: Some bacteria can grow in acid substrates

Neutrophiles: most microbes prefer a pH near neutrality

Alkalinophiles: Microbes which can grow in very alkaline substrates

 Control of microbial growth

Sterilization: Removal or destruction of all microbial life forms

Physical Methods of Microbial growth Control:

 Heat:

Moist heat:

 Coagulation (denaturing) of proteins

 Hydrogen bonds are broken

 Boiling:

 Not always effective

 Kills most vegetative pathogens, viruses, fungi and spores within 10 minutes

Some microbes resistant to boiling e.g. endospores (20 Hours)

 Autoclave:

Preferred method

 Moist heat (steam) and pressure

 Limitations: Material must be able withstand heat and moisture

 15 psi (121° C) for 15 minutes will kill all organisms

 Pasteurization (Louis Pasteur):

 Mild heating (Initially 63° C for 30 minutes)

 Kills most pathogens and bacteria that cause spoilage

 Lowers bacterial numbers

 Preserves taste of product

 High temperature short – time pasteurization (HTST)

 Kills pathogens

 Lowers bacterial numbers, milk keeps while refrigerated

 Dry Heat Sterilization

 Flaming

 Incineration

 Hot air sterilization: Placed in oven (170 ° C for 2 hours)

 Filtration:

 Liquids and heat sensitive materials

 Filters composed of cellulose or plastic polymers. Vacuum assists gravity

 Small pores prevent passage of bacteria (0.1μm -1mm)

Sterilization by filtration

 Low Temperatures (Refrigeration):

 Bacteriostatic (stop microbial growth)

 Psychrotrophs still present and grow

 Slow freezing more harmful to bacteria than rapid.

 Ice disrupts the cell structure

 Thawing damages bacteria as well

 High Pressure:

 Applied to liquid suspensions

 Alters protein shape

 Endospores are resistant

 Can be killed by altering pressure cycles

 Endospores germinate then exposed to pressure again

 Desiccation:

 Removal of water

 Microorganisms cannot grow but still survive

 Re –introduce water microorganisms resume growth and division

 Effectiveness varies between organisms

 Neisseria withstand dryness for one hour

 Mycoplasma withstand dryness for months

 Endospores remain for centuries

 Osmotic Pressure:

 High concentrations of salt and sugar

 Creates hypertonic environment

 Water leaves microbes cell

 Molds and yeasts can grow better than bacteria in high osmotic pressure or low moisture

 Radiation:

 Ionizing radiation (gamma rays)

 High energy short wavelength

 Radioactive elements

 X- rays

 Penetrate deeply

 Require longer times

 Ionizes water to form hydroxyl radicals

 Food preservation in other countries

Chemical Methods of Microbial Growth Control:

Examples of some chemicals used for microbial growth control:

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