Lactobacillus Acidophilus Growth

[deleted-858583]

Hello,
I am researching the impacts of artificial sweeteners (sucralose, acesulfame potassium, aspartame, saccharin) on the growth of lactobacillus acidophilus. I purchased five tubes of the freeze dried viable cultures from Carolina and am planning to inoculate the bacteria for 48 hours at 37° C in the provided medium. After, I plan to expose the bacteria to a solution made of artificial sweetener and distilled water and again incubate them for 48 hours at 37 °C in the same test tubes and growing media. I hope to analyze the amount of bacterial growth when exposed to each of the artificial sweeteners compared to the untouched control. However, I am concerned as how to tell if the bacteria are alive or dead. Is there a way to determine if bacteria grown in liquid media are alive or dead? Thank you for your help.

[deleted-785995]

Hi there!

This sounds like a great project idea! I'm not sure if you have access to a microscope, but that is usually the easiest method to determine whether bacteria are viable. There are other methods that require more sophisticated equipment, but a microscope should suffice for your project.

If you have extra media, you could try to grow more of your bacteria from an isolate of your original culture, but it can be difficult to validate what you're growing (aka if you have contamination) without a microscope.

Best of luck!

[deleted-860560]

You would count all bacteria as an absolute number. The way this is done is to report the number of bacteria for a microliter. There are specialized microscope slides for this (Which are normally used for blood cell counts) referred to as cell counting slides. The process for an accurate count is basically the same basic process for doing a manual Complete Blood Count (CBC), where you can find lots of tutorials on the internet about how it's done. The only exception to this would be the study of an anti-biotic type property, e.g. if you were studying the effectiveness of a substance to kill a specified bacteria.

That said, you wouldn't grow bacteria in the medium and then inncoulate the grown bacteria with the scientific variable (e.g. the sweetner) Rather, you would use two separate but identical growth mediums incubated under identical conditions, one with the sweetner and one without, which is the control.

[pharrast]

Another option would be to mix the solutions as bakertaylor said, and then spread the solutions with bacteria on different agar plates. After a day or two, you can count the number of colonies with the naked eye! One way to be objective about it if you have too many colonies to count is to draw lines on the plates and count only a couple small portions on each plate. Some sweeteners may lead to zero which can be your answer. Or, you can do the experiment again and wait longer to see if colonies eventually show up in all of groups.