Clostridia

Clostridia are a diverse group of obligate anaerobes, spore-forming, rod-shaped bacteria that play various roles in the environment, human health, and disease. They include both non-pathogenic species that contribute to gut homeostasis and pathogenic species that can cause severe infections and intoxications
Guo et al. 2020b Journal of Animal Science and Biotechnology 11: 24

Clostridia are known for their ability to produce resistant dormant cells that can withstand heat, desiccation, and toxic chemicals.

Clostridia are among the predominant bacteria in the human [large intestine]; but they are also found in soil, and water(brain://QPZxhOYHq0CebAhpYkseNw/DistalColonColonLargeIntestine).
Ohashi & Fujisawa 2019 Bioscience of Microbiota, Food and Health 38(2): 65-68

Patients with diarrhea exhibited increased Clostridia compared to no diarrhoea patients Touchefeu et al. 2014 Aliment Pharmacol Ther 40: 409-421

Clostridia have the potential for harmful pathogenic effects (Salminen et al. 1998) and is decreased in Inflammatory Bowel Disease (IBD).