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BIO 205 – Microbiology
Chapters 8, 9, end of Ch. 3
Chapter 8 - Growth of Microorganisms
Key words / concepts
•doubling / generation time•binary fission•the growth phases of a population
• lag, exponential, stationary, death•colony•biofilm•trance elements vs. growth factors•temperature “requirements”•oxygen requirements•pH and salt “requirements”•bacterial counts•dilution plating / spread plate technique
How do most bacteria replicate?
Some do it a bit different . . .
Listeria monocytogenes
Generation time
Growth Phase
Continuous culture in a chemostat
Types of Growth
Streak plate technique
Biofilms
Biofilms and quorum sensing
Biofilms
Microbial nutrition
Microbial nutrition
Trace elements
Growth factors
Nutritional classes of microorganisms
carbon from CO2
Defined media Produced from pure chemicals
Complex media Extracts of natural sources
▪ Beef, blood, milk, protein, yeast, soybeans
▪ Precise composition not known Selective media
Contents select for specific microorganism
Differential media Identification of microorganisms
Defined media none
Complex media Nutrient agar Mueller Hinton agar - antibiotic testing
Selective media EMB - inhibit growth of Gram positive bacteria MacConkey - inhibit growth of Gram positive bacteria Mannitol salt - high salt (staph will grow)
Differential media Sheep Blood agar - hemolysis EMB - lactose and/or sucrose fermentation - fecal
coliforms MacConkey - lactose fermentation Mannitol Salt - mannitol fermentation - pathogenic staph Enterotube - rapid ID of enteric bacteria (15 tests in 1) Synder - dental caries susceptibility - acid producers in
saliva
How temperature affects growth
Oxygen requirements
aerobe
anaerobe
obligate / strict
facultative
microaerophile
aerotolerant
Oxygen culturing conditions
• Culturing– Shaking machines
• Increase oxygen in the media
– Candle jars• Not anaerobic but
reduces available oxygen
– Anaerobic chambers• All oxygen is replaced
with other gas Figure 3.25
How do we visualize oxygen requirements in the lab? (stab vs. broth)
pH and salt and bacterial growth
halophilic
How do you know how much bacteria there is?
How do you know how much bacteria there is? Hemocytometer
Viable count = dilutions and plating
Pour vs. spread plate technique
Plate count
A little math for you!
plate 1 ml of bacteria onto agar plate
5348 672 126 28
Summary - Growth of Microorganisms
Chapter 9 - Controlling Microorganisms
How we used to protect ourselves from microbes
Sterilization
Disinfection / sanitizing
Decontamination
Antiseptics / antisepsis
Bactericide vs. Bacteriostatic
Methods of Physical Control
Heat
• moist heat
• dry heat
cold
Preserving cultures
• Cold storage– Short-term: refrigeration slows growth
• Must continually transfer
– Long-term: freezing• Add substance to reduce freeze-killing
– Glycerol, skim milk, dimethyl sulfoxide (DMSO)
– Lyophilization• Long term—freeze drying• Frozen and dried under vacuum• probiotics
Methods of Physical Control
autoclave incineration
Sterilization
Eliminating all microorganismsCulture media must be sterilizedHeat sterilization
Moist heat▪ Autoclave▪ 121oC for 20 minutes
Dry heat▪ 170oC for 90 minutes
Figure 3.20
Methods of Physical Control
pasteurization
Thermal Death What?
Thermal Death Time
Thermal Death Point
Methods of Physical Control
Radiation
• nonionizing (UV)
• ionizing
Methods of Physical Control
Methods of Physical Control
Filtration
Lyophilization
Methods of Chemical Control
germicides - activity classified as
high intermediate low
Assignment for next week:What do you use (at home or work)? How does it work?
Methods of Chemical Control
•Phenols / phenolics
•Alcohol
Methods of Chemical Control
• Halogens
• Hydrogen Peroxide
Methods of Chemical Control
•Heavy metals
• Surfactants / detergents
Testing germicides
we will do Nov. 9
Testing germicides
Less light = higher concentration of toxin = less bacteria still alive
Highest ConcentrationOf toxin
Preserving Food
Preserving Food
Fig. 1. Flow diagram of the main routes of spore contamination into foods. A circled Sp indicates possible environments for formation of endospores (sporulation).
