What is mesophilic starter cultures?

Starter cultures that grow best between 18 - 32 C (65 - 90 F).

Used for the production of fermented milk products, fresh cheese, soft cheese, semi-hard cheese, hard cheese and butter.

e.g. Probat M 4, 505 & Probat 222, Choozit Alp D (gas formers)

e.g. Choozit 230,  Choozit 102,  Choozit Alp, Choozit Feta B & A
(O-cultures, which mean they do not ferment citrate, therefore no gas normally)

What is thermophilic starter cultures?

Starter cultures that grow best between 37 - 45 C ( 99 - 113 F).

Thermophilic starter cultures are mainly used for the production of

yoghurt, hard cheese and soft cheese.

Lactobacillus Cultures (strong acidifying) Used for hard cheese and varioud types of Italian cheese, where cheese making is performed at a relativ high temperature.

e.g. Lb. bulgaricus (yoghurt), lb. helveticus (cheese)

e.g. St. thermophilus cultures (mild souring in yoghurt & cheese)

e.g. Probiotic Cultures such as Bifidobacteria, Lb. acidophilus,
Lb. casei & Lb. rhamnosis.

Joghurt 621 contains St. thermophilus and Lb. bulgaricus
Jo-Mix 401 is a mild multi-species culture.
JoMix 215 is mild also with bifido +
Lb acidophilus, Lb. lactis & st. thermophilus

So as you can see each has its purpose.
When you are looking for cultures do not hesitate to ask
question.
It is important you get you on the right track from the start.