SIBO: symptoms and treatments of this infection ?

The term SIBO stands for "small intestinal bacterial overgrowth" and refers to a bacterial swarm of the small intestine, which is characterized by an excessive number of bacteria in this part of the intestine and malabsorption. Diarrhoea, flatulence and malabsorption symptoms are the most common clinical manifestations. The factors predisposing to bacterial swarm are either anatomical (diverticulosis, blind loop, etc.) or functional (disorders of intestinal motor skills, absence of gastric acid secretion). Treatment consists of a high-fat, low-carbohydrate diet, the management of deficiencies, broad-spectrum antibiotic therapy and the avoidance of promoting factors in order to avoid recurrence.

What is SIBO ?

The term SIBO means" small intestinal bacterial overgrowth " or bacterial overgrowth of the small intestine. It is characterized by an excessive number of bacteria in the small intestine (>105 / ml) that can cause malabsorption disorders, that is, insufficient assimilation of food substances.

What causes SIBO ?

In normal conditions, the proximal part of the small intestine contains less than 105 bacteria / ml, mainly Gram-positive aerobic bacteria. This low bacterial concentration is maintained by :

• the effect of normal intestinal contractions (or peristalsis) ;
• normal gastric acid secretion ;
• mucus ;
• secretory immunoglobulins A ;
• a functional ileocaecal valve.

In case of bacterial swarm, an excess of bacteria, > 105 / ml, is found in the proximal intestine. This can be related to :

• abnormalities or anatomical changes in the stomach and / or small intestine (diverticulosis of the small intestine, surgical blind loops, post-gastrectomy states, stenoses or partial obstructions) that promote slowing of intestinal contents, leading to bacterial proliferation ;
• digestive tract motor disorders associated with diabetic neuropathy, scleroderma, amyloidosis, hypothyroidism, or idiopathic intestinal pseudo-occlusion that may also decrease bacterial evacuation ;
• an absence of gastric acid secretion (achlorhydria), which may be of medicinal or surgical origin.

What are the symptoms of SIBO ?

The most common bacterial species in case of bacterial swarm of the small intestine include :

• Streptococcus sp ;
• Bacteroides sp ;
• Escherichia coli ;
• Staphylococcus sp ;
• Klebsiella sp ;

and Lactobacillus.

These excess bacteria reduce the absorption capacity of intestinal cells and consume nutrients, including carbohydrates and vitamin B12, which can result in carbohydrate malabsorption and nutrient and vitamin deficiency. Moreover, these bacteria also act on bile salts by altering them, they prevent the formation of micelles which leads to malabsorption of lipids. Severe bacterial swarm finally leads to damage to the intestinal mucosa. 

Many patients have no symptoms. In addition to initial weight loss or deficiencies in nutrients and fat-soluble vitamins (including vitamins A and D), the most common symptoms include :

• abdominal discomfort ;
• more or less severe diarrhoea ;
• steatorrhea, that is, an abnormally high amount of lipids in the stool, resulting from lipid malabsorption and mucosal damage ;
• bloating ;
• excessive flatulence, caused by gases produced by the fermentation of carbohydrates.

How to cure SIBO ?

Antibiotic therapy should be put in place, not to eradicate the bacterial flora but to modify it in order to obtain an improvement of the symptoms. Due to the polymicrobic nature of the intestinal flora, broad-spectrum antibiotics are needed to cover all aerobic and anaerobic bacteria.

The treatment of SIBO is thus based on taking, for 10 to 14 days, orally, one or two of the following antibiotics :

• Amoxicillin / clavulanic acid 500 mg 3 times / day ;
• Cephalexin 250 mg 4 times / day ;
• Trimethoprim / sulfamethoxazole 160 mg / 800 mg 2 times / day ;
• Metronidazole 250 to 500 mg 3 or 4 times/day ;
• Rifaximin 550 mg 3 times / day.

This broad-spectrum antibiotic treatment can be cyclical or even modified, if symptoms tend to recur.

At the same time, factors that promote bacterial overgrowth (anatomical and functional abnormalities) should be eliminated and a change in diet is recommended. This is because excess bacteria metabolize mainly carbohydrates in the intestinal lumen rather than lipids, a diet high in fat and low in fiber and carbohydrates - lactose - free-is advocated. Vitamin deficiencies, in particular vitamin B12, must also be corrected.