Lactobacillus brevis - Part II

Here are the results from the plating experiment! 

1. Apple Juice Agar

No growth! Sorry for the poor pic quality - those whitish specks are surface marks on the Petri dish, and not colonies. 

2. Malt Extract Agar

Good growth, with a confluent morphology. This may be from swarming due to the relatively higher pH of malt agar. 

3. Modified MRS agar

Good growth, with discrete white colonies. 

4. Lactose-MRS agar

Again with discrete colonies, but growth is less luxuriant than modified MRS. 

It is surprising that nothing grew on the apple juice agar. I used a brand that claims to be 100% pure juice with no preservatives, but clearly there's something that's inhibiting the growth of Lactobacillus in it. Perhaps a natural preservative that doesn't need to be/wasn't declared? Fishy! 

Growth was best on the modified MRS agar compared to Lactose-MRS, suggesting that Lactobacillus may indeed prefer simple sugars. The evident growth on malt extract agar however suggests that at a pinch, simple malt extract agar can indeed be used to grow Lactobacillus brevis. If you have also noticed, the colony count is quite different from the estimated/theoretical count based on dilution - this is especially evident when looking at both the MRS plates. I was expecting about 20 colonies, but this turned out to be way more than that. I have to admit it is probably due to an error in dilution - I did use a very accurate micropipette to measure out volumes less than 1ml, but I got lazy during the dilution and used a sterile 5ml syringe for the sterile water. That may have accounted for some of the inaccuracy, but thankfully absolute count wasn't really the primary measure in this quick plating experiment. My wife will probably give me no peace for such shoddy measurements. :) 

As a follow-up to this, I have prepared culture flasks/slants containing all 4 media. I plan to slant the Lactobacillus into them for storage, but this time they will not be in an anaerobic environment.