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Small Bowel Bacterial Overgrowth (SBBO)

Define SBBO?

SBBO usually is defined as an overgrowth of more than 105 CFU/mL of bacteria in
the proximal small bowel.

Discuss the mechanism of malabsorption in SBBO?

Malabsorption is due to the intraluminal effects of proliferating bacteria (degrading CHO and protein, using up B12) combined with damage to mucosal enterocytes. This damage lead to diminished disaccharidase activity; decreased transport of monosaccharides, amino acids and fatty acids; and protein losing enteropathy.
Fat malabsorption results from bacterial deconjugation of bile salts to form bile acids. These are readily absorbed in the jejunum leading to insufficient concentrations for normal fat absorption.
Discuss the disorders associated with bacterial overgrowth?
Growth of bacteria in small bowel is normally controlled by the ability of gastric acid to kill swallowed microorganisms and the cleansing effects of normal intestinal motility. Immunoglobulins in intestinal secretions and an intact IC valve are also important.

  • Small intestinal stasis-
    • Anatomic abnormalities- Small intestinal diverticulosis, surgically created blind loops (end-to-side anastomosis), Strictures (Crohn’s disease, radiation, surgery)
    • Abnormal small intestinal motility- Diabetes mellitus, Scleroderma, Idiopathic intestinal pseudo obstruction, Radiation enteritis, Crohn’s disease.
  • Abnormal communication between the proximal and distal gastrointestinal tract- Gastrocolic or jejunocolic fistula, Resection of the ileocaecal valve.
  • Associations usually with multifactorial causes- Hypochlorhydria due to atrophic gastritis or medications (These are usually not clinically significant unless there coexist concomitant motility disturbances of the small bowel, so malabsorption may be precipitated by the use of PPI in scleroderma), Immunodeficiency states (common variable immunodeficiency, AIDS, severe malnutrition), Chronic pancreatitis, Cirrhosis, Alcoholism, End stage renal disease, Advanced age (mechanisms not fully understood)

Some authorities think that SBBO is perhaps the most discernible cause of malabsorption in geriatric populations.
Discuss the clinical features of SBBO?
Abdominal discomfort, bloating, diarrhoea, flatulence, wt loss, weakness, neuropathy
Discuss the diagnosis of SBBO?
Patients should be tested and treated for SBBO in the presence of symptoms and a known predisposition to SBBO even in the absence of malabsorption.

  • Small bowel (jejunal) aspiration and culture- ideal but cumbersome
  • 14C glycocholate breadth test- small bowel bacteria would deconjugate this bile salt releasing 14CO2. Specificity is poor because of colonic bacterial deconjugation of unabsorbed bile slat when there is ileal damage or resection
  • H2 breadth tests- Breath hydrogen testing is performed by administering a test dose of carbohydrate (usually lactulose or glucose). Excess bacteria in SBBO breakdown CHO to release H2. Breath hydrogen testing is safe, easy to perform, and can be used in women of child-bearing age and children as no radioisotope is involved.

In these breath tests, the diagnosis of SBBO is established when the exhaled breath H2 level increases by more than 10 parts per million greater than baseline on 2 consecutive samplings or if the fasting breath hydrogen level exceeds 20 parts per million. In patients with SIBO and an intact intestine, a peak occurs within 1 hour and is less prominent than the normal colonic peak.

The specificity is compromised when hydrogen is produced by colonic bacteria, especially when transit times are accelerated by the osmotic load of the substrate dose. Further upto 18% of persons are H2 non excretors. The test will false negative in these pts as H2 is metabolised by bacteria to methane.
Discuss the treatment of SBBO?

  • Correct the underlying small intestinal abnormality, if possible
  • Antibiotics- Effective antibiotic treatment should cover both aerobic and anaerobic enteric bacteria. A single course of therapy for 7 to 10 days may improve symptoms and have an effect lasting for months.
  • Adequate antimicrobial coverage can be achieved with the following combinations: Amoxicillin-clavulanate (500mg tds), metronidazole (250 tds), ciprofloxacin (250 BD), rifaximin (1200mg/day), doxycycline (100 BD) etc
  • In some symptoms promptly recur on stopping antibiotics.  Recurrent SBBO can be treated by cyclic (e.g. 1 week of 4) or continuous long-term antibiotics. Rotating antibiotic regimens may help to prevent the development of resistance.
  • Prokinetics may help propel bacteria through the stagnant small bowel
  • Nutritional support- replace deficient vitamins. Avoiding lactose- as lactase deficiency develops in many pts with SBBO.

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