chapter 12

bacteria growth

increase in cell number, parent cell doubles in size and duplicates cell contents

budding

small new cell develops on the surface of an existing cell, yeast does this

binary fission

cell duplicates its contents and divides into two cells, most bacteria does this

bacterial growth curve

1. Lag phase

   1. organisms are active but not increasing that much in numbers

   2. they are getting reading to divide by increasing in size

   3. may be 1 hr to multiple days depending on species

2. Log phase

   1. organism adapted to environment

   2. growth occurs logarithmically or exponentially

   3. dividing at their most rapid rate

   4. can take 20 min to 20 hrs to double in size (generation time)

3. Stationary phase

   1. limitation of nutrients

   2. new cells produced at the same rate old cells die

4. Death phase

   1. medium becomes less favorable

   2. less nutrients, space, and more waste

   3. dying at logarithmic rate

   4. some produce spores

quorum sensing

molecular signaling system that lets other bacteria know what is out there and coordinate processes with each other like bio film

biofilm

large community of bacteria in one spot that is like a slimy layer and its a community where different bacteria have different jobs

sociomicrobiology

study of how bacteria behave and interact with each other

colony forming unit (CFU)

when a single bacterium is deposited on a plate it divides to form a colony

a colony is a distinct growth and clones from a single cell

count colonies to determine the number of cells on a plate

why are CFUs an underestimation

• not every cell will survive on a plate

• 2 organisms might be too close so both colonies look like a single colony

• nutritional requirements

2 ways to obtain CFUs

• streaking for isolation

  • useful for getting single colonies

• dilution plates

  • each amount of sample that you spread around the whole plate is diluted each time

  • useful for determining how many organism are in a specific sample

ways to count colonies

1. directly count CFUs on a plate

2. use a hemocytometer

   1. put a sample of bacteria on a coverslip and slide with wells and a grid

   2. count the number of bacterial cells in the squares of the grid

selective media

• encourages the growth of some organisms but suppresses others

• ex: MSA and MAC plates

  • MSA has high salt concentration so organisms that can’t survive in salty environments won’t grow

  • selective for gram + and differential for mannitol fermentation bc it has a pH indicator and has mannitol in it

differential media

• has an ingredient that causes an observable change when a biochemical reaction occurs

• ex: MAC, MSA

  • MAC differential for lactose fermentation bc it has a pH indicator and has lactose in it

    • turns yellow when there is not a lactose fermentor

  • also it is selective for gram - bacteria bc it has crystal violet and bile salts

enrichment media

has special nutrients in it for example blood agar and chocolate agar (lysed blood cells)

nutritional influences on bacteria growth

availability of carbon, nitrogen, sulfur, phosphorus, trace elements, vitamins

physical influences

pH, temp, oxygen concentration, pressure, etc

temperature influence on growth

• most enzymes have an optimal temp that is near the organisms optimal temp where the have the highest activity

• when the temp gets too high the enzymes denature —> can’t carry out organisms function and organism dies

• organisms that infect humans have similar optimal temp to humans

names of organism classifications at optimal temp

0-20º C —> psychrophile

15-45 —> mesophile

40-70 —> thermophile

70 - 100 —> extreme thermophile

pH influence on growth and classifications

• enzymes work best at optimum pH and have a range

• pH 0.1 to 5.4 —> Acidophile

• Neutrophiles pH 5.4 to 8.0

• Alkaphiles pH 8.0 to 11