Review for 10.1186/s12876-021-01613-y (2021)

Reviewer’s report
Title: 
Short chain fatty acids and colon motility in a mouse model of irritable
bowel syndrome
Version: 
1 
Date: 
30 Nov 2020
Reviewer's report:
I would like to thank the authors for 
adding 
new data on transit 
by performing
artificial pellet propulsion measurement in mouse colon in vitro and their
through revision of the discussion. However on rereading I do have some further
thoughts you might like to consider
1. Statement " However, there are no reliable data on fecal SCFAs concentrations
in IBS patients and animal" needs modifying You could quote the meta-analysis
by Sun (1)
3 . I am still puzzled by the statement "The anaerobic index decreased from -
0.352±0.052 ru in control to - 0.437±0.052 ru (n=5, p<0.05) which indicates an
overgrowth of facultative anaerobic bacteria. The reference (2) given points out
how increasing oxygen levels favours facultative anaerobes but does not report
any link between this and the ratio C3+C4/C2. Can you find a better justification
for this statement which validates the link between the Ai and redox potential.
Specifically are there studies where redox potential has been measured using a
redox meter and correlated with the Ai ?
4. I am also 
confused by the nomenclature since a fall in redox potential
indicates a more anaerobic environment which would not favour facultative
anaerobes which are associated with a rise in redox potential (3) . Furthermore it
is unclear why the ratio is negative?
5. You quote ref 53 to link butyrate to motility yet need to acknowledge that the
picture is far from clear since ref 53 shows butyrate enemas slow distal transit
not accelerate it 
6. Reference 28 refs to rats not patients so better to omit from that sentence
7. I do think there should be some discussion about the relevance of 
the high
concentrations of SCFA used in the incubation studies. Blood levels of butyrate
and pripionate are umolar and acetate is undetectable in human serum. The
luminal concentrations used are more physiological so I think these results are
more likely to relate to in vivo conditions
References
1. Sun Q, Jia Q, Song L, Duan L. Alterations in fecal short-chain fatty acids in
patients with irritable bowel syndrome: A systematic review and meta-analysis.
Medicine. 2019;98(7):e14513-e.
2. Rigottier-Gois L. Dysbiosis in inflammatory bowel diseases: the oxygen
hypothesis. The ISME Journal. 2013;7(7):1256-61.
3. Million M, Raoult D. Linking gut redox to human microbiome. Human
Microbiome Journal. 2018;10:27-32.
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