How to measure growth differences with Bacteria?

Question

How to measure growth differences with Bacteria?

Answer 1

Ok, first you weigh the empty petri dish without bacteria. Then you weigh the one with bacteria, do some math and there you have the weight of the bacteria. However, you would have to have a pretty sensitive scale to measure the weight of bacteria... How much does bacteria weigh, .00001 grams? Most scientists count bacteria colonies that develop over time and track their progress that way as they see what factors contribute to their growth.

Answer 2

excelent

your planning is not bad at all. the overll approach is good and you have thought it through

now..the devlil is in the details

the machine is probably a spectrophotometer. it measures how much light is absorbed by a solution. a solution with a lot of suspended material in it [like...oh i dont know..say a whole load of bacteria] would absorb a lot of light. there are wel known standards for calculatign bacterial concentration his way..go google them. then try to remember the terms etc, it impresses people more if you can use the right name, not 'the mesury-thing' :)



now..your specific questions... 5 plates? no.

in an ideal situation you would want to use the rule-of-threes.

so...for each concentration you do 3 plates, and treat all teh the same [so you have 3 plates treated the same, you count the bacterial growth on each one and get the average...this makes your results statisticaly more accurate]



yes you wil be able to see/count the colonies quite easily.





my suggestions...



grow up the bacterial culture to about 100000000 cells/ml. thats a good, cloudy lookign solution. then dilute it down using growth-medial [do a 1 in 10 dilution, then a 1-in-10 dilution of that, then a 1-in-10 dilution of that etc etc] right down to 1000 cells/ml. that last solution is about 100cells in 100ul [there are 1000ul in 1 ml].



test 3 bacterial concentrations. i would suggest you want to be adding [in triplicates remember] 100 bacterial, 1000 bacterial and 10,000 bacteria.

thats 9 plates already.

we need to have a set of these 9 plates for the negative-control [so this is the set where you add no soap]

then you are looking to test the concentration of the soap and how effective it is.



i would suggest diluting the soap.

a 1/10 dilution, a 1/100, a 1/1000 and a 1/10000 dilution.

so, we are now up to 47 plates.

ask for an even 50 plates and you wil have spares

if you have any plates left at the end you could add undiluted soap to a few of the plates to see the effect [but this should nuke the hell out of any poor bugs]



for your calculations you first count up the un-treated, or negative-control plates. eg, you know that you added 100 cells [you added 100ul of the 1000 cells/ml [or 1000 cells/1000ul] solution] to 3 plates. count how many grew. if you have roughly 100 colonies then you know 2 things....

1- your dilutions are good

2- your techniques good.

if you have 50 when you expect 100 then you know that you are loosing about 50% of what you plate out. understand?

dont forget to get the average for the 3 plates, an average of just 1 plate is worthless



now...this data from the untreated plates is important. you are looking to calculate the %-killing by the different solutions, so you need to know how many bacteria would be there without soap and then how many are there with the soap, the difference is the %-killing



so...count the cells on he plates with added soap and calculate [the average of the 3 plates for each group] the % killing

then plot a quick graph showing increasing concentration and increasing bacterio-cydal effect



good luck and i hope it works out.

if you have to reduce the number of plates, try duplicates insted of triplicates

try missing out the middle concentrations of the soap, just do 1/10 and 1/10000

keep the untreated standards though, you will need these

Answer 3

Below is the Link for a short communication btw

Johannes Rouska, , and Nalini M. Nadkarnib from Lund University



If you click on source below you will find all the related tables and formullas ;)

Good Luck



aDepartment of Microbial Ecology, Lund University, Ecology Building, Solvegatan 37, SE-223 62 Lund, Sweden



bThe Evergreen State College, 2700 Evergreen Parkway, Olympia, WA 98505, USA





Received 24 November 2008; revised 25 January 2009; accepted 6 February 2009. Available online 26 February 2009.

Answer 4

After you make the solution with bacteria (called broth culture), you measure the cell density (or growth) of bacteria using a spectrophotometer at an 600 nm wavelength.In this step use the media you used to culture the cells as the blank.



then you need to do serial dilution of the bacterial culture and then use the spread plate method to introduce bacteria into the agar plates..

then place the antibacterial discs ( 2 of them onto the plates using sterile forceps..



If antibacterial discs are not available, you could make paper discs using a punching machine and then pour 5 to 10 microlitres of the antibacterial substance onto the discs..



Following incubation for 24 to 48 hours, a zone of clearance can be observed around the discs..this happens because the anti-bac substance diffuses from the disc and destroys the bacteria.



measure the zone of clearance to determine which detergent is the most effective.



this is the best method as far as i know..

about the concentration of the bacterial solution-- it is best to do serial dilution upto 10^-4...

and you also could do serial dilutions of the detergent..

the number of plates you need will depend on the number of anti-bac detergents u are using...



the entire expt must be done in a laminar flow hood..

just mail me if u need help...