Actinomycetes and Bacillus are spore producing bacteria. Bacteria are single-celled organisms. While bacteria can be helpful and most are harmless, there exists harmful types of infectious bacteria that have the potential to make people extremely sick. Some bacteria produce endospores ( or internal spores) that may be allergenic. Endospores are resistant to hash environmental conditions. The most well know endospore (spore) producing bacteria belong to the genus Bacillus. Bacillus is a gram-positive, rod-shaped bacterium. Bacillus thrive on dead or decaying organic material. The spores are commonly found in soil, dust, and water.
Actinomycetes (or filamentous bacteria) is another group of spore forming bacteria. Actinomycetes are thermophilic. That is, their optimal temperature for growth ranges from 37 to 60°C. For example, Thermoactinomyces candidus grows fast between 55 and 60°C and will not grow at 37°C or below. In wet or damp indoor environments the most commonly encountered genera of actinomycetes are Micropolyspora, Thermoactinomyces, and Saccharomonospora.