Microbes in Household Products

Probiotics are live micro-organisms which, when taken in adequate amounts, give a health benefit to the host.
They include species of Lactobacillus and Bifidobacterium and some yeasts.
They are taken as a live microbial food supplement, for example in curd, yoghurt and other fermented milk products.
On ingestion they beneficially affect the host by improving the balance of the intestinal microflora and checking the growth of disease-causing microbes.
They are not antibiotics (which are chemicals that kill microbes), not allergens and not cancer-inducing microbes.
So probiotics are live microbial food supplements.

Dough for bread or idli contains yeast (Saccharomyces cerevisiae) or bacteria.
In warm conditions these microbes ferment the sugars in the dough anaerobically, producing ethyl alcohol and carbon dioxide:
$C_6H_{12}O_6 \rightarrow 2C_2H_5OH + 2CO_2$
The $CO_2$ gas gets trapped in the dough as bubbles, making it rise and become soft and spongy. Warm weather speeds up the activity of the microbes.
The $CO_2$ is produced inside the dough, not absorbed from the atmosphere.
So the dough becomes soft and spongy because of fermentation.

Bread dough is mixed with baker's yeast, Saccharomyces cerevisiae.
The yeast ferments the sugars in the dough, producing ethanol and carbon dioxide: $C_6H_{12}O_6 \rightarrow 2C_2H_5OH + 2CO_2$
The $CO_2$ gas forms bubbles that make the dough rise; on baking, the bread becomes soft and porous (spongy), and the alcohol evaporates.
So bread becomes porous due to $CO_2$ released by the action of yeast.