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

Culture media Defined media Complex media Selective 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

Culture media that we will use Defined media none Complex media Nutrient agar Mueller Hinton agar - antibiotic testing

Culture media that we will use 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 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

plate 1 ml of bacteria onto agar plate 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 microorganisms Culture media must be sterilized Heat 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

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).