You can't be sure...It is a qualitative method normally used to carry out the initial strain selection.

Dear

The growth on CaCO3 MRS agar media is one step for lactic acid bacteria isolation but the growth condition under anaerobic.

You are right that other acids may also react with CaCO3 and produce clear zone. MRS with CaCO3 can only be a screening method to isolate lactic acid bacteria from samples. Other methods should be further employed to identify the presumptive colonies. If you only want to know if the colonies are lactic acid bacteria or not, you can further determine the morphological, physiological and biochemical characteristics of the colonies using microscope and API 50 CHL kit. If you want to determine the specific strains of the bacteria, genotypic identification should be used. The genomic DNA of the colonies will be extracted, sequenced and compared to GeneBank database to determine the specific strain.

Same as Yezhi Fu's answer. Also, Gram staining should be done after purification. Motility and catalase tests can also be included.

This is a preliminary step but became old in recently. OK it could be LAB. Because many species can do such reaction now. I prefer to run other fast identification step by Vitek-2. It takes only 48 hours.

You can easily differentiate Lactobacillus from other related bacteria through oxygen requirement for growth (-), Catalase test (-), Oxidase test (-), Benzidine test (-), Nitrate reduction (-), Endospores (-), Motility test (+-), and m-A2PM (+-) in cell wall.

You need simple test for screening many isolates. Most lactic acid bacteria can produce acid curd in skim milk medium. Then, you can use biochemical confirmation tests, API, Vitec, Biolog or genetic methods for accurate identification.

Lactic acid bacteria are facilitative anaerobes, so I am not sure if the test for O2 requirement is really needed. Gram positive, catalase negative and non-spore forming bacteria can be initially considered as lab which can be confirmed by 16S rRNA gene sequence analysis.