Science Buddies: "Ask an Expert"

Hello. I actually only have a simple question. Let's say I have a broth solution that had already been inoculated and incubated. After incubation, there were no changes on the physical appearance of the solution. However, you just want to make sure that there really weren't any growth so you plan to analyze that sample solution using a spectrophotometer. You first read a blank solution and then read your sample solution. Is it okay to use a spectrophotometer to makes sure that your sample solution has no bacterial growth? My guess is that you can, but I'm not so sure.'ve been trying to find answers almost everywhere.

Many thanks to whoever will answer this.

Hi, thanks for the question! The simplest way to tell if there is significant bacterial growth in your broth is to look at the telltale signs: cloudiness, chunks, and possible rings (sometimes the bacteria will float or sink in the broth). Even though bacteria is microscopic, data-significant colonies should appear under the naked eye.

However, if a near exact measurement of bacterial growth is desired, it would be possible to incubate some of the broth in a sterile medium (a petri dish) and then you'd determine the number of colonies per volume. Certain equipment that detects bacterial byproducts (such as oxygen) is very useful in determining the volume and presence of bacterial colonies.

Good luck with your experiment!