over the counter bactericidal/bacteriostatic compounds for growth media

[KyleWolf]

Hey everyone.

I traditionally don't use slants or plates for yeast isolation and growth, but I now have a few reasons (other than just curiosity) to do so.

I have what I suspect is a lightly infected culture of a retired yeast strain that I am very partial to. I want to do a culture on an agar medium to isolate a single colony. At the same time I don't want to pull any potential bacteria with it (I know, isolation techniques are made just for this reason, but I am just being cautious).

I am a microbiologist by trade, so I do have access to antibiotics like Ampicillin Pen/Strep, etc. but I figured if I am doing this at home, might as well find a way to do it that people at home can reproduce.

So, long story short, I am looking for something I can add to my media (DME/agar) that has bactericidal or bacteriostatic properties to allow the yeast, but not bacteria, to grow. I thought about hops, honey, or garlic. I know they aren't antibiotics, but I they could at least give the yeast an advantage.

Thoughts?
TL;DR- looking for something to reduce bacterial growth on agar/slants.

 

[DudleyDoLeft]

unsure the best regime -
Within what I can think of perhaps a combination with isolating, growing it as a small starter. washing with chlorine dioxide then feeding and plating it again would be the best method.

I do not understand about the methods of using other substances on plates. but due to potential altering factors or stresses on the yeast it seems to me that if a accepted brewing method is used, coupled with sensory perception of the starter, perhaps microscope visual inspection.. resulting in a plate that is purely wort and agar that is clean this may be for the best.

-Adding other material may certainly be worth a try but also could add too much uncontrollable factor or warp or mutate the yeast away from the same floculation, viability or flavor properties.

 

[AK7007]

I usually do successive streaks onto selective media (antibiotics). I've never used home remedies as a way to separate yeast from bacteria, but do commonly spike my malt agar plates with hops as a light antibacterial.

Main caution I'd give though - don't use raw honey. It contains dormant lactobacilli. I've isolated them through rehydration and subsequent streaking, then grown up a starter for a quick sour beer.

Best course of action is going to be to use Amp plates. I don't actually know that spiking with hop pellets does anything for me, but I do it anyways for normal plates.

 

[KyleWolf]

I had never thought of doing a chlorine dioxide wash nice idea! I take it you have done that and it is pretty effective? I would have thought it would damage the yeast too, but again I can see why it wouldn't.

AK7007- Where do you get your Amp from? I know I can get it from my lab or places like Sigma and the like, but I figured for the everyday homebrewer it wasn't a viable option. Also, the honey wouldn't be raw, it would have been boiled with the malt and agar. I like the idea of culturing the lacto though. How much hops do you spike with? I am interested in doing a few experiments.

 

[bucketnative]

ClO2 is used as a sterilant in pharma and med device, which means that it has been shown to be effective against all microorganisms. In fact, here's some marketing literature from ClorDiSys (ClO2 gas sterilant), where they mention the effectiveness of ClO2 against Saccharomyces cerevisiae: http://www.clordisys.com/pdfs/articles/bioprocess_part_1.pdf

 

[KyleWolf]

Right, I know is can be used as a sterilant, it's what we use to de-con our BSL-3 lab space. Though I imagine for the application DudleyDoLeft is probably using the ClO2 water treatment tablets. I is quite possible it is time dependent (a small amount of time to kill bacteria, a longer time required for yeasts).

 

[bucketnative]

Right, I know is can be used as a sterilant, it's what we use to de-con our BSL-3 lab space. Though I imagine for the application DudleyDoLeft is probably using the ClO2 water treatment tablets. I is quite possible it is time dependent (a small amount of time to kill bacteria, a longer time required for yeasts).

The article I linked to also discussed liquid ClO2 applications. I work with another chemical sterilant (similar in nature) on the med device side, and I know that for our process, the yeast (candida) are typically less resistant than bacteria (particularly spore formers). You may be able to find D-value results somewhere in the literature for aqueous ClO2 and different organisms; that would give you the relative kinetics of inactivation.

You also might want to consider if the ClO2 would be mutagenic towards the yeast that did survive. that would be another literature dive.

 

[KyleWolf]

Those are excellent points and thank you for the clarification! With that I don't think I would be using the ClO2. Maybe I will just ditch the whole home remedy and grab some Amp from the lab haha.

 

[Anatidaephobic]

Do you have a pH meter and have you considered passing a small batch of the yeast through an acid wash?

Normally brewers use phosphoric acid to lower the pH to around 2.2 and hold it there for 2 hours at fridge temp. This kills off the vast majority of bacteria, but not yeast. It may decrease the viability of the yeast somewhat though. If you really wanted to go for the home remedy you could try lemon juice. I've read anecdotally that even star san can be used.

 

[trentm]

Hops are very effective in suppressing the growth of some lactobacillus species/strains. However some have adapted to a beer (therefore hop) environment. ClO2 is being used to "wash" yeast slurries destined to re-pitch in commercial breweries. Here is link to a bit of info on that: http://www.brewingscience.com/
You might consider acidifying your media to ~pH 4. Yeast like that pH but many bacteria don't (LABs excluded). It is likely that your contaminate is an LAB as these are the most common beer spoilage organisms. I was just reading where corriander has bacteriostatic properties and is used in making Biltong to suppress bacterial growth during drying. Of course salt (NaCl) suppresses bacterial growth but not sure about yeast (many Brett strains are salt tolerant). While I have no experience sorting out yeast from a bacterial contaminated culture, I have often had success in separating Brett from Sacch in a mixed culture without any selective media. In that situation, you can enrich the culture with wort, incubate for about a week. After that time, most of the sacch will have dropped out of suspension and you can simply do a dilution streak from the upper portion of the liquid and pick out the Brett and/or Sacch after colonies have developed. The advantage here is Brett is slow to grow on a plate compared to Sacch. So it's easy to pick out a Brett colony (it's the small one). But with Sacch you cannot be sure there is not Brett within the apparent Sacch colony. You would have the same issue sorting out bacteria as many bacteria grow slower (colony size not necessarily numbers of cells) on plates compared to Sacch.

 

[Legume]

http://www.allivet.com/mobile/p-2377-fish-mox-amoxicillin.aspx?gclid=CPa158_fnswCFdKIfgodeJACVQ

antibiotics are commonly used in aquariums to treat fish diseases.