Just a quick question,

I carried out an experiment and got my bacteria to grow from (3.56 X 10(7)) to (8.5 X 10(8)) in 11 hrs.

My question is that if I half the initial inoculation amount, will it take double the time to reach the same number of bacteria? That is if I inoculate(1.78 X 10(7)) number of bacteria into the medium, will I get (8.5 X 10(8)) bacteria after 22 hrs?

Depends what growth stage they are in: i.e. lag, log, stationary, or death phase. But in a perfect world, yes.

Need to do a growth curve. Because bacteria can grow exponentially, it may only take 1 hour long to reach that number if they can replicate in 1 hour...


If you add half the inoculum and they replicate one time per hour, in one hour you will have already made up that difference.

Inoculum can be tricky, which is why I say do a growth curve. Start with different inoculums of a standard culture. For instance, do an overnight (16 hour culture), then use that to inoculate 50 mls. Inoculate 50 ul in 50 mls (1/1000), 100 ul (1/500), 500 ul (1/100), and 1000 ul (1/50), then take OD readings every few hours to see how well it grows.

With the bacteria I work with, I can get a 7x10^9 cfu/ml in 16 hours from a 1/100 inoculum. However, if I do a 1/1000 inoculum, I hardly get anything grown in 36 hours.

Im calculating this for my growth curve... Initially i carry out the experiment in 2ml medium just to estimate the time it takes to reach a certain OD because besides the growth curve, im also uusing it for other purpose.. kills 2 bird with 1 stone..

so I inoculate 50 microlit of OD 0.922 culture into 1ml and got the OD after 11 hrs...

This time Im trying to scale up to 100ml and I want it to reach the same OD in 48 hrs...

So I thought maybe if I half the initial amount I might get to the OD in 48 hrs..

By the way I have carried out enumeration so I know the exact number of bacteria corresponding to the OD

one problem you might find when scaling up is the availability of oxygen in the media. Small volumes are easier to aerate than larger volumes. So large volume cultures tend to take longer to reach the desired saturation. (which can be compensated for starting with a larger inoculation.)

To your original question - the minor difference ("halving the inoculum" of 10^7 cells/ml ) is a pretty trivial change. The numbers alomost fall within standard error of plate count. It should not take twice as long under the same conditions - it should be accomplished in about the same time - perhaps a little longer.

Sure agree with pernese - scaling up will change dynamics so you can't accurately predcit the effect on growth rates. I also wonder at the excessive precision reported.