. 2016 Aug 19;14(8):e1002533. doi: 10.1371/journal.pbio.1002533

Table 1. Bounds for bacteria number in different organs, derived from bacterial concentrations and volume.

Location	Typical concentration of bacteria ⁽¹⁾(number/mL content)	Volume (mL)	Order of magnitude bound for bacteria number
Colon (large intestine)	10¹¹	400 ⁽²⁾	10¹⁴
Dental plaque	10¹¹	<10	10¹²
Ileum (lower small intestine)	10⁸	400 ⁽⁵⁾	10¹¹
Saliva	10⁹	<100	10¹¹
Skin	<10¹¹ per m² ⁽³⁾	1.8 m² ⁽⁴⁾	10¹¹
Stomach	10³–10⁴	250 ⁽⁵⁾–900 ⁽⁶⁾	10⁷
Duodenum and Jejunum (upper small intestine)	10³–10⁴	400 ⁽⁵⁾	10⁷

⁽¹⁾ Except for skin, concentrations are according to [9]. For the skin, we used bacterial areal density and total skin surface to reach an upper bound.

⁽²⁾ See derivation in section below.

⁽³⁾ Skin surface bacteria density is taken from [11].

⁽⁴⁾ Skin area calculated as inferred from standard formula by DuBois for the body surface area [12].

⁽⁵⁾ Volume of the organs of the gastrointestinal tract is derived from weights taken from [13] by assuming content density of 1.04 g/mL [6].

⁽⁶⁾ Higher value is given in [14].