It is important to know the most predominant bacteria in each part of the gastrointestinal tract. In the upper G.I.T the aerobic organisms are more common as in stomach we can find lactobacilli or streptococcus species. While in the lower G.I.T we can find anaerobic organisms more than aerobes as in large intestine we find bacteroides and lactic acid bacteria are more common. This graph shows the dominant organisms in the major parts of gastrointestinal tract along with its function.