The safety of probiotics is tied to their intended use, which includes consideration of potential vulnerability of the consumer or patient, dose and duration of consumption, and both the manner and frequency of administration.

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3023597/

Common side effects of too many probiotics can lead to bloating, gas, and nausea. People at greater risk of dangerous side effects are those with a weakened immune system or serious illness, in which case you should consult a doctor before taking large amounts of probiotics. https://www.insider.com/can-you-overdose-on-probiotics

The recommended doses range from 1 billion to 10 billion colony-forming units (CFU)—the amount contained in a capsule or two—several days per week. A daily supplement for one to two weeks may improve conditions such as infectious or antibiotic-related diarrhea. https://www.health.harvard.edu/press_releases/benefit_of_probiotics_should_you_take_a_daily_dose_of_bacteria

I'm no expert but I have a keen interest in the area of probiotics.

Before you even begin to prove safety, you need to consider if it is actually worth using. Are you wanting a product which only benefits while the person is taking them and not actually colonise? There are already many products that do this.

The complexity of the microbiome is only just beginning to be understood. A probiotic that is beneficial for one person will likely NOT be beneficial to most others.

Each new species and strain you wish to introduce, needs to fit into an existing group of species and strains in the intestines of the person you want to have lasting benefits in.

There are so many products with multiple strains added that have never been shown to be able to co-exist so they all are pretty much a waste of time. And when you consider most products have only a small number of strains compared to the 1000s of strains in the typical microbiome, commercial products appear to me at least, a waste of time.

You would be better to try to commercialise a probiotic product with hundreds of species and strains. Maybe you could start with a good kefir where the strains already are happy to co-exist and turn this range into a capsulated product.

First I need to find out which strains are in each product of mine, so I am studying and knowing the variety of them in the studies, I disagree with you that a basic formula may be useful for different people, but discussing this would be a waste of time if you already have convictions, the only thing I'm sure of is that this is possible with the right combination, and many researchers say that it takes hundreds, it looks like an imitation of the answer, I'm a researcher I will test with different combinations it seems to me that combining hundreds is laziness or fear of making mistakes, so with hundreds the answer will be almost universal, it will have strains compatible with anyone, but whoever delivers the product has no idea what they are for each person, so their claim of benefit is a bit of a fraud, and if not work, if the strains that benefit the person are the weakest colony, that's why it is better to study before stating

Andre you missed completely what I was getting at.

The reason probiotics don't colonise is because one strain is not allowed to colonise in most peoples guts, whereas a large group that already co-exist and know how work together, have a much better chance. They protect each other. Groups of probiotics that have not grown together, will fight with each other and with the recipients species and strains.

As far as I'm concerned, probiotics that don't colonise, are a waste of time. They really are ripping off the consumer.

Agree with you sir @Jacobsimons

Kindly check https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3023597/

These microorganisms are ubiquitous, and hence going to expose in variable body physiology and organisms, normally if we check their Hemolytic Activity, , recognition of Virulence factor ,Antibiotic Susceptibility, Bile Salts Hydrolysis. It will be further assure the safety.