Review Reports

Round  1

Reviewer 1 Report

The manuscript: “Analysis of health benefits conferred by Lactobacillus species in kefir” by Slattery et al aimed to shed light on the direct and indirect impact of some specific lactobacillus strains on several in vitro and in vivo experimental models. 

General comments

The article offers a very interesting review/overview on both the key and even lacking evidences for the specific role of such various lactic acid bacteria strains on animal and human health. It is always a “tricky” issue to comment or circumvent a review paper, as it depends on author's choice and selected opinions. The collected information and the comments that are generated in this paper are consistent and useful, especially those dealing with the anti-infection processes. The specific field of Kefir as “probiotic provider” is unexplored and this paper may serve as a state of the art. It is resctricted to lactobacilli from Kefir origins. Comparison with similar effects and lactobacilli from other fermented produt could be a plus.

The authors deliberately decided to describe such potentials “strain after strains” rather than based on the distinct mode of actions. Although it is less conventional, it has the merit to emphasize on the extreme importance of the strain dependent effects.

The MS is clear and concise and the discussion through all the text is well conducted and documented. I do appreciate the section dealing with the knowledge gaps.

Some involved mechanisms in immunomodulation and anti-oxidant properties are evoked in a very superficial way to my opinion, but I acknowledge that it was not the main purpose of the review. (I mean that it is not a referee’s exigency …). Similarly, the distinct role of the matrix is not much discussed and most examples are based on strains derived or isolated from Kefir but cultivated in laboratory culture media.

 Anyway, according to the general value of this paper that strengths the concept that (i) colonic metabolism is a key point to control human health including further development of systemic metabolic syndrome and (ii) data are still lacking and required more and appropriate studies to substantiate specific Kefir-based intervention; I consider it suitable for publication in Nutrients and I recommend that it could be accepted in its present form.

 As a specific remark,

1. the beginning of the sentence L692 is missing.

2. L763-766: “The anti-diabetic effects” … As mentioned by the authors, data are not consistent and out of the scope; so I suggest this short paragraph be discarded.

3. Should the title be “Analysis of health benefits conferred by Lactobacillus species from kefir” rather than “… Lactobacillus species in kefir” as most studies described here are not using whole kefir (to feed mice or even clinical studies) but single strains, without providing the role of other bacteria and yeasts ?

 Author Response

Response to Reviewer 1 Comments
Point 1: the beginning of the sentence L692 is missing.
Response 1: We thank the reviewer for his observation, and the text has been corrected accordingly.
Point 2: L763-766: “The anti-diabetic effects” … As mentioned by the authors, data are not consistent and out of the scope; so I suggest this short paragraph be discarded.
Response 2: Upon reviewing the paragraph, we agree with the reviewer in this regard, and this paragraph has been discarded.
Point 3: Should the title be “Analysis of health benefits conferred by Lactobacillus species from kefir” rather than “… Lactobacillus species in kefir” as most studies described here are not using whole kefir (to feed mice or even clinical studies) but single strains, without providing the role of other bacteria and yeasts ?
Response 3: Agreed, "from" kefir is the most accurate term, and the sentence has been altered accordingly.

Reviewer 2 Report

Dear Authors,

You have written a detailed review, with many good critical side notes to the literature that was discussed. High quality of scientific content and flawless language. I have a few small comments:

 Page 5, line 277. Please provide a small comment on the meaning of decreased NPC1L1 in the text.

 Page 7, line 390. Is the amount of detected bacteria shed in the faeces a good measure for colonisation? Shouldn't there also be a microbial assessment of the intestinal mucosal layer to be 100% sure that colonisation has not occurred? It would be good to make a small comment on this issue.

 Page 8, line 424. Although it is a promising result, the statement that high doses of Lb. kefiranofaciens are certainly within a safe range can be misleading. The study was performed in rats and it could be read as though the safety will also automatically apply to humans. This statement deserves a more precise and cautious wording.

 Page 14, line 692. There appears to be a part of the sentence or paragraph missing, please insert the appropriate text.

 Page 14, line 724. Please elaborate a bit more on how increased Th1 cytokines or an altered Th1/Th2 balance can fit well with the observed decreases in expression of genes involved in the classical and lectin complement pathways, this could also be an interesting field for further research.

 Page 14, line 727. What do you mean by environmental factors? And, if this strain acts on TLR2 to alleviate DSS induced colitis, isn't it a more tempting assumption that by ligating TLR2, the intestinal barrier is tightened, releasing less intestinal content into the surrounding tissues, with a subsequent decrease of inflammatory cytokine production? TLR2, if dimerised with the right partner and ligated by the right ligand, can stimulate anti-inflammatory reactions and PKC-isoform activation that leads to barrier tightening.

 Page 15, Conclusions. I agree that it is of great scientific interest to link each beneficial health effect to a certain strain, just for the sake of knowledge, and to research the underlying mechanisms. However, if we want to harnass the beneficial effects, wouldn't it be of much more use to set up human studies with people being supplemented with full kefir, and then measuring (the feasible) physiological parameters and looking directly into their faecal microbiome, but including analysis of functional groups of the microbiome? Isn't it likely that the combined effects of this ingested ecosystem are stronger than the separate strains? Please address these issues in brief.

Author Response

Response to Reviewer 2 Comments
Point 1: Page 5, line 277. Please provide a small comment on the meaning of decreased NPC1L1 in the text.
Response 1: An explanatory comment has been added.
Point 2: Page 7, line 390. Is the amount of detected bacteria shed in the faeces a good measure for colonisation? Shouldn't there also be a microbial assessment of the intestinal mucosal layer to be 100% sure that colonisation has not occurred? It would be good to make a small comment on this issue.
Response 2: We thank the reviewer for their observation, and have clarified the language surrounding this section. 
Point 3: Page 8, line 424. Although it is a promising result, the statement that high doses of Lb. kefiranofaciens are certainly within a safe range can be misleading. The study was performed in rats and it could be read as though the safety will also automatically apply to humans. This statement deserves a more precise and cautious wording.
Response 3: Agreed. We have altered the interpretation of this finding accordingly.

Point 4: Page 14, line 692. There appears to be a part of the sentence or paragraph missing, please insert the appropriate text.
Response 4: We thank the reviewer for this observation ,and have corrected it accordingly.
Point 5: Page 14, line 724. Please elaborate a bit more on how increased Th1 cytokines or an altered Th1/Th2 balance can fit well with the observed decreases in expression of genes involved in the classical and lectin complement pathways, this could also be an interesting field for further research.
Response 5: We have added a further discussion on the putative link between the downregulation of these pathways with the upregulation of of Th1 cytokines. 
Point 6: Page 14, line 727. What do you mean by environmental factors? And, if this strain acts on TLR2 to alleviate DSS induced colitis, isn't it a more tempting assumption that by ligating TLR2, the intestinal barrier is tightened, releasing less intestinal content into the surrounding tissues, with a subsequent decrease of inflammatory cytokine production? TLR2, if dimerised with the right partner and ligated by the right ligand, can stimulate anti-inflammatory reactions and PKC-isoform activation that leads to barrier tightening.
Response 6: We have clarified the language surrounding the use of the term "environmental factors", and have included the assumption regarding TLR-2 and the strengthening of the intestinal epithelium.
Point 7: Page 15, Conclusions. I agree that it is of great scientific interest to link each beneficial health effect to a certain strain, just for the sake of knowledge, and to research the underlying mechanisms. However, if we want to harnass the beneficial effects, wouldn't it be of much more use to set up human studies with people being supplemented with full kefir, and then measuring (the feasible) physiological parameters and looking directly into their faecal microbiome, but including analysis of functional groups of the microbiome? Isn't it likely that the combined effects of this ingested ecosystem are stronger than the separate strains? Please address these issues in brief.
Response 7: We thank the reviewer for this observation, and have added a clarifying section towards the end of the conclusion.