Chapter 6 Microbial Growth

cell growth definition

increase in number of cells, not size

physical requirements for cell growth

• temperature

• pH

• osmotic pressure

primary groups of temperature (3)

• psychrophiles

• mesophiles

• thermophiles

psychrophiles def

cold loving microbes

mesophiles

moderate temperature living microbes

thermophiles

heat loving microbes

food preservation danger zone temperature

15-50 C
60-130 F

what happens in the danger zone temperatures

bacteria grows rapidly, some produces toxins

most bacteria grow between a pH of

6.5 - 7.5

molds and yeasts grow at a pH between

5 - 6

acidophiles grow in

acidic environments

hypertonic environments def

increase in salt/sugar

hypertonic environments cause

plasmolysis

what is carbon

structural organic molecule

which troph uses organic carbon sources

chemoheterotrophs

which troph uses CO2

autotrophs

where does nitrogen appear

amino acids and proteins

most bacteria ____ proteins

decompose

bacteria who use N2 is also known as

nitrogen fixation

where does sulfur live (3)

• amino acids

• thiamine

• biotin

where can we see phosphorus (4)

• DNA

• RNA

• ATP

• membranes

obligate aerobes

• aerobic

• grows at the top

• oxygen required

facultative anaerobes

• anaerobic and aerobic

• grows throughout tube

• oxygen present

• grows better when there is O2

obligate anaerobes

• anaerobic

• bottom of tube

• no oxygen

aerotolerant anerobes

• anaerobic

• throughout the tube

• oxygen present

microaerophiles

• aerobic

• middle of tube

• oxygen required

organic growth factors

• vitamins

• amino acids

biofilms

microbial communities that form hydrogels

biofilms are sheltered from

• desiccation

• antibiotics

• immune system

biofilms are involved in 70% of infections. Name a few

• catheters

• heart valves

• contact lenses

culture medium

nutrients prepared for microbial growth

sterile

no living microbes

inoculum

introduction of microbes into medium

culture

what microbes grow on

agar

solidifying agent for culture media in petri plates, slants, deeps

agar is made of

complex polysaccharide

chemically defined media

exact chemical composition is unknown

complex media

extracts and digests of yeasts, meat, or plants

examples of complex media

• nutrient broth

• nutrient agar

anaerobic culture methods

reducing media

what is reducing media

when you have a chemical that binds to O2 so you heat it off to get rid of the O2

capnophiles

microbes that require high CO2 conditions

examples of capnophiles

• CO2 jar

• candle jar

selective media

suppresses unwanted microbes and encourages desired microbes

differential media

makes it easy to distinguish colonies of different microbes

enrichment culture

encourages the growth of desired microbes

how is enrichment culture different than selective media

it’s designed to increase numbers of desired microbes to detectable levels

pure culture

contains only one species

streak plate method

isolates pure cultures

2 methods of preserving bacterial cultures

• deep freezing

• lyophilization (freeze drying)

deep freezing temperatures

-50 -to -95 C

lyophilization temperatures

frozen and then dehydrated in a vacuum

generation time

time required for a cell to divide (20 minutes to 24 hours)

phases of growth

• lag phase

• log phase

• stationary phase

• death phase

4 DIRECT methods of measuring cell growth

• plate counts

• filtration

• most probable number

• direct microscopic count

3 INDIRECT methods of measuring cell growth

• turbidity

• metabolic activity

• dry weight

plate count advantages

measures the number of viable cells

plate count disadvantages

• long incubation time

• bacteria forms in clumps (CFU)

• too many to count

best plate count ratio

1:10,000

counting bacteria by membrane filtration advantages

• study microbes in diluted sample

• doesn’t require time

counting bacteria by membrane filtration disadvantages

hard to count

most probable number

• useful for microbes who will not grow on solid media

• useful for using differential mediums to identify microbes

advantages of direct microscopic count

• no incubation time

disadvantages of direct microscopic count

• motile microbes are difficult to count

• dead cells are also counted

• high concentration of cells are required to be countable

metabolic activities purpose

measures the amount of metabolic products such as acid or CO2

dry weight

used for filamentous bacteria and mold