Small Bowel Bacterial Overgrowth
Small Bowel Bacterial Overgrowth
Small Bowel Bacterial Overgrowth
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<strong>Small</strong> <strong>Bowel</strong> <strong>Bacterial</strong> <strong>Overgrowth</strong><br />
Stephen A. McClave,MD<br />
Professor of Medicine<br />
University of Louisville School of Medicine<br />
Louisville, Kentucky
Introduction<br />
• Definition<br />
Abnormal bacterial proliferation in upper SB<br />
>10,000 colony forming units (cfu/ml)<br />
Syndrome of weight loss, diarrhea and malnutrition<br />
Malabsorption of macro and micronutrients<br />
• History<br />
1897 - Association between bowel strictures and Vit<br />
B 12 deficiency (pernicious anemia)<br />
1939 - Association due to bowel stasis and bacterial<br />
overgrowth (“putrefaction”)
Normal Intestinal<br />
Ecology<br />
• <strong>Bowel</strong> colonization<br />
Sterile (birth) → Full flora at 1 month<br />
Factors – Gestational age,<br />
delivery, feeds<br />
• Levels of colonization<br />
Stomach to jejunum – sterile up to<br />
1,000-10,000<br />
10,000 cfu/ml<br />
Ileum – higher concentration<br />
100,000-1,000,000,000 1,000,000,000 (10 9 ) cfu/ml<br />
Ileocecal valve – steep gradient, some stasis<br />
Colon – Mainly anaerobes<br />
10 9 -10<br />
12 cfu/ml
Variance in <strong>Bacterial</strong> Species<br />
“Good Guys”<br />
“Bad Guys”<br />
Faculative Anaerobes<br />
Gram Positives<br />
True Anaerobes<br />
Gram Negative<br />
Coliforms
Normal Intestinal Ecology<br />
Beneficial Effects of Enteric Bacteria<br />
• <strong>Bacterial</strong> enzymes (disaccharidases) break down carb<br />
sugars to short chain fatty acids to be absorbed in colon<br />
• Some meds require bacterial metabolism for their action<br />
• Enteric bacteria produce folate, vit K<br />
• Enteric nonpathogenic bacteria (“good(<br />
guys”)<br />
prevent colonization by pathogenic orgs (“bad(<br />
guys”)
Host Defense Mechanisms<br />
• Gastric acid<br />
• Intestinal motility<br />
• Intestinal secretions with immunologic properties (IgA)<br />
• Bacteriostatic pancreatic and biliary secretions
Conditions Favoring<br />
SBBO<br />
• Anatomic<br />
SB diverticulosis<br />
Intestinal strictures (Crohn’s, XRT, Ca)<br />
Surgical blind loops (BII, JI bypass)<br />
• Motility disorders<br />
Scleroderma<br />
Diabetic autonomic neuropathy<br />
Idiopathic intestinal pseudoobstruction<br />
• Achlorhydria<br />
Surgical<br />
Atrophic gastritis, chronic H. Pylori
Conditions Favoring SBBO<br />
• Abnormal connections between proximal and distal bowel<br />
Resection IC valve<br />
Fistulas (Crohn’s, PUD, Ca)<br />
• Immunodeficiency states<br />
Common variable immunodefic<br />
Acquired immunodeficiency<br />
Malnutrition<br />
• Other conditions<br />
Cirrhosis<br />
End-stage renal disease<br />
Chronic pancreatitis<br />
Fistula
Pathogenesis of SBBO<br />
• Fat malabsorption<br />
Bacteria unravel (deconjugate) ) bile acids<br />
A toxic lithocholic acid is produced<br />
Action of bile salts
Gut<br />
Lumen<br />
Brush<br />
Border<br />
Pathogenesis<br />
of SBBO<br />
Carbohydrate metabolism<br />
Bacteria digest carbs<br />
Fermentation (hydrogen, CO 2 )<br />
Maldigestion, , osmotic load,<br />
diarrhea, pain
Pathogenesis of SBBO<br />
• Protein metabolism – lesser effect<br />
Bacteria degrade proteins, reduce AA absorption<br />
Less output of pancreatic protease enzymes
Pathogenesis of SBBO<br />
• Alterations in vitamin metabolism<br />
Bacteria utilize Vit B 12<br />
Fat-soluble<br />
Vits A,D,K,E malabsorbed<br />
Bacteria produce folate, Vit K
Clinical features<br />
• Predisposing past history<br />
Surgery<br />
Diabetes<br />
Scleroderma<br />
Crohn’s Disease<br />
Immunodeficiency<br />
Radiation Rx<br />
• Usual symptoms<br />
Asymptomatic<br />
Diarrhea<br />
Weight loss<br />
Abd pain<br />
Bloating<br />
Steatorrhea<br />
• Symptoms related to deficiencies<br />
Night blindness (Vit A)<br />
Osteomalacia (D)<br />
Anemia (B 12 ) Loss of balance (B 12 )
Diagnosis<br />
• <strong>Small</strong> bowel aspirate ( Dx >10 5 cfu/ml )<br />
Special tube to avoid contamination<br />
Best test for now<br />
• Bile acid breath test ( radiolabeled carbon C 14* )<br />
<strong>Bacterial</strong> deconjugation liberates glycine*<br />
Poor test (↓(<br />
specificity, sensitivity)<br />
• D-Xylose<br />
breath test ( radiolabeled carbon C 14 * )<br />
SB absorption occurs before sugar reaches colon<br />
Metabolism produces 14 CO 2 *<br />
Good test (85% pos 1 hr, 100% pos 3 hr)<br />
• Hydrogen breath test<br />
Bacteria ferment carb (lactulose) ) to produce H 2<br />
Early peak (represents SB) vs late peak (represents colon)<br />
Poor test (sensitivity 55%, false pos and neg)
Treatment<br />
• Correct fluid, electrolyte, nutrient deficiencies<br />
• Correct underlying anatomic abnormalities<br />
Surgery<br />
Promotility agents – Reglan, Octreotide,<br />
Erythromycin<br />
• Empiric antibiotic therapy<br />
Rationale – Rx aerobes, O2 kills anaerobes<br />
Examples – TCN, ampicillin, Flagyl, Septra<br />
Monotherapy 7-107<br />
days – Some sustained remission<br />
Rotating combination more effective<br />
• Probiotic therapy – unproven as yet<br />
Examples – Yogurt, lactobacillus GG, Saccharomyces Boulaardi<br />
Promote growth of nonpathogenic “good guys”
Syndrome of<br />
D-Lactic Acidosis<br />
• Definition – Syndrome of<br />
neurologic dysfunction<br />
• Predisposing factors<br />
Short bowel<br />
Intact colon<br />
• Physiology<br />
Fermentation of carbohydrates<br />
Production of D-LactateD<br />
• Diagnosis<br />
Metabolic acidosis<br />
Lab assay for D-Lactate D<br />
(Mayo Clinic)<br />
• Treatment<br />
Limit carbohydrates (simple >> complex)<br />
Antibiotics<br />
TPN, bicarbonate
Conclusions<br />
• Clinical consideration in complex patient<br />
• Identifying likely candidates<br />
• Empiric diagnosis and treatment
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