Lactulose breath hydrogen test and Enterotest string test were carried out simultaneously on 19 children 3–5 years old. Bacteria isolated from the jejunal fluid in upper small intestines of these children were incubated with lactulose at neutral pH. Anaerobes were present in all but one child, and in 15 children they were present in numbers greater than 5 log10 organisms per ml. Most of these bacteria did not produce hydrogen in vitro. Hydrogen production (>100 ppm) was observed with the following bacteria: Bacteroides (5%), Clostridia (8%), anaerobic corynebacteria (5%), Escherichia coli (67%), Lactobacillus (8%), Staphylococcus (8%), and Streptococcus (9%). The following bacteria did not produce hydrogen in vitro: Actinobacter, Actinomyces, anaerobic cocci, Bifidobacterium, Fusobacterium, micrococci, Neisseria, Sarcina, and Veillonella. This study suggests that in the diagnosis of small bowel bacterial overgrowth using lactulose breath hydrogen test, it is important to consider that patients with a flat breath hydrogen response to a carbohydrate challenge during the first 60 min may be infected with enteric bacteria which are not capable of producing H2.
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