Final answer:
The most prevalent bacteria in the human gut are Bacteroides, comprising about 30% of the gut microbiome and playing a vital role in the digestion and inhibition of pathogens. Hence, option (c) is correct.
Step-by-step explanation:
The bacteria that are most prevalent in the human gut are the Bacteroides species. They make up about 30% of the gut microbiome, and one gram of human feces can contain up to 100 billion Bacteroides cells. While many bacteria are present in the gut, Bacteroides are particularly important because they help digest plant food and prevent pathogenic bacteria from colonizing the large intestine.
Their presence can be reduced following antibiotic use, which sometimes leads to secondary infections due to an increase in pathogenic bacteria and fungi. Therefore, Bacteroides play a crucial role in maintaining a healthy balance of microbes in the gut.