exp 28: effect of osmotic pressure on microbial growth

define hypotonic

low solute content with a higher osmotic pressure in the cell

define hypertonic

high solute content = growth may be inhibited

what does the degree of inhibition rely on?

type of solute and nature of the organism

staphylococcus aureus

halo-tolerant: grows on skin, tolerant to salt

halobacterium salinarium

halophile: likes and needs high salinity to grow

effect of osmotic pressure on growth

why are bacteria generally resistant to hypotonic environments whereas animal cells are not?

the presence of a rigid cell wall in bacteria helps them resist the osmotic influx of water in hypotonic environments. animal cells, lacking such a protective structure are more susceptible in hypotonic conditions and need to actively regulate their internal osmotic balance to prevent damage

how do hypertonic environments negatively affect most bacterial cells?

hypertonic environments cause bacterial cells to lose water, resulting in cell shrinkage, plasmolysis and potential cell death

why are staphylococci well suited for colonization of skin?

ability to produce adhesive molecules that enable them to adhere to and colonize the skin’s surface + tolerance

explain how foods can be preserved using salt or sugar. give two examples of foods preserved this way

salt or sugar is added to foods, creating a hypertonic environment that draws water out of microorganisms, thereby inhibiting their growth and preventing spoilage

ex. salted fish and preserved fruit jams