Chapter 13.15 : Quantitative Culture of Small-Bowel Contents

Abstract:

The microbial content of the normal gastrointestinal tract varies with the precise site ( 2 , 5 ). The concentration of bacteria in gastric aspirates from fasting patients is fewer than 103/ml. Duodenal and jejunal organisms are normally present at fewer than 105/ml ( 3 ) and consist of primarily gram-positive bacteria (staphylococci, streptococci, and lactobacilli) and yeasts. Members of the family Enterobacteriaceae are occasionally present in small numbers. Strict anaerobes are notably absent. Postprandially, the microbial content of the proximal small bowel is increased by the introduction of food and oropharyngeal microorganisms. The ileal microbiota more closely resembles that of the colon, with the ileocecal valve incompletely regulating backwash from the colon. In the distal ileum, the bioload consists of 107 to 108 aerobes and anaerobes per ml, whereas in the colon, a significant rise in anaerobes to 1010 to 1011 organisms per ml and of aerobes to 108 organisms per ml is found ( 3 ). (See Appendix 13.15-1 for further discussion.)