Overgrowth of the indigenous gut microbiome and irritable bowel syndrome

Table 1 Studies investigating the prevalence of small intestinal bacterial overgrowth in patients with irritable bowel syndrome, using culture-based assessments of proximal small intestinal luminal secretions

Country	IBS patients	Controls	Mean age (yr)	Aspirate details	Definition and prevalence of SIBO in patients and controls
Sweden[21]	n = 162 IBS-D, n = 49 IBS-C, n = 37 IBS-A, n = 76	n = 26, healthy	IBS: 38Controls: 40	Non-fasting; via water-perfused manometry catheter from jejunum	≥ 105 CFU/mL colonic-type bacteria:	IBS patients	7/162 (4%)
						IBS-D	2/49 (4%)
						IBS-C	3/37 (8%)
						IBS-A	2/76 (3%)
						Controls	1/26 (4%)
					≥ 5 × 103 CFU/mL colonic-type bacteria:	IBS patients	17/162 (11%)
						Controls	1/26 (4%)
					≥ 5 × 103 CFU/mL any bacteria:	IBS patients	70/162 (43%)1
						Controls	3/26 (12%)
The Netherlands[22]	n = 8 (out of a cohort of 12 symptomatic patients)	n = 9, healthy	Symptomatic: 39Control: 26	Fasting; via weighted catheter from jejunum	> 105 CFU/mL colonic-type bacteria:	Symptomatic patients	1/12 (8%)
						Controls	0/9 (0%)
					Colonic-type bacteria: Enterobacteriaceae≥ 103 CFU/mL, Bacteroides species ≥ 102 CFU/mL or Clostridium species ≥ 102 CFU/mL	Symptomatic patients	1/12 (8%)
						Controls	0/9 (0%)
United States[23]	n = 148	n = 527, symptomatic	Overall: 53	Fasting; via endoscopy from duodenum	≥ 105 CFU/mL colonic-type aerobic bacteria OR ≥ 104 CFU/mL anaerobic bacteria:	IBS patients:	2%
						Controls	10%
Greece[24]	n = 112 IBD-D, n = 35 IBD-C, n = 19 IBD-A, n = 58	n = 208, symptomatic	SIBO: 63.6No SIBO: 69.5	Fasting; via endoscopy from duodenum	> 105 CFU/mL colonic-type aerobic bacteria:	IBS patients	24/112 (21%)2
						Controls	11/208 (5%)
					> 103 CFU/mL colonic-type aerobic bacteria:	IBS patients	42/112 (38%)2
						IBS-D	21/35 (60%)25
						IBS-C	6/19 (32%)3
						IBS-A	15/58 (26%)4
						Controls	20/208 (10%)

¹P = 0.002 compared to controls;

²P < 0.0005 compared to controls;

³P = 0.012 compared to controls;

⁴P = 0.003 compared to controls;

⁵P = 0.001 compared to controls. IBS-D: Diarrhoea predominant-type irritable bowel syndrome; IBS-C: Constipation predominant-type irritable bowel syndrome; IBS-A: Alternating-type irritable bowel syndrome; CFU: Colony forming units; SIBO: Small intestinal bacterial overgrowth; IBS: Irritable bowel syndrome.