They remain solid, as very few bacteria are able to decompose agar (the exceptions being those in the following genera: Cytophaga, Flavobacterium, Bacillus, Pseudomonas, and Alcaligenes).
Most cultures available contain a research based consortium of Microbial cultures, containing all necessary microorganisms (B. licheniformis, B. thurengensis, P. polymyxa, B. sterothemophilus, Penicillium sp., Aspergillus sp., Flavobacterium, Arthrobacter, Pseudomonas, Streptomyces, Saccaromyces, Triphoderma, etc.).