Growth curve - (May/13/2014 )

hello! My question is quite basic as i havent done this before or learned it.

.I am working on antibacterial tests and i normally incubate bacteria for 18hrs at 37C ..later i dilute it to 01OD to get an approx of 10OE8.But for reassurance i want to know in which stage is the bac at 18hrs incubation .so what i do is basically take a single colony and put it in 10ml broth..then start from time zero until 18hrs reading OD at hourly basis or take 0.1microliter and perform serial dilutions and enumerating by plate counting. First is that correct?? Second how would i determine the growth over all the 18hrs?! How to manage reading after 15-18 hrs??And pls if anyone has a written method to follow i greatly appreciate if you share it.Thx in advance for your comments And help..!

At 18th hr. bacterial culture will be in declining phase of growth- Next expected phase is stationary phase. But if you want to monitor growth after 18th hr. you need to replenish culture nutrient and remove products - sort of continuous culture.

Inbox's comments are only relevant for fast growing bacteria such as E. coli - other species may well have a different profile.  The easiest and best way to determine the stage of growth is to do a growth curve - every hour or so take a sample and measure absorbance at OD600, read and plot the graph of absorbance over time.  You can do CFU too if you wish, but it will be more or less pointless for early time points up to about 3 hours or more depending on strain and species.

Thx a lot for the replies!! But if i do monitor the growth on hourly basis by taking a sample and reading its OD on spectro. How can i continue this in the late night until early next day?? Do i incubate another culture at the end of that same day till the next morning and coninue reading hourly basis ? Any idea pls?

It depends on how much you take out - you can get cuvettes that will work with as little as 100 ul.  You could also replace the culture back into the broth.    For your early time points you don't need to sample so often, every 2 hours will probably be fine, it should be more frequent as the cells enter log-phase growth, and you can do less frequent again as the population plateaus.

Thx again for the helpful tips!