La policaprolactona o PCL

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The association between relative abundance of F. prausnitzii, D. formicigenerans, B. longum and ponderal (weight-related) growth has been shown before in murine studies. A study that compared fecal microbiota composition of mice transplanted with fecal samples from malnourished or healthy Malawian children reported a positive association between relative abundance of B. longum, F. prausnitzii, D. formicigenerans and weight gain in mice that harbored fecal samples from healthy children76_{. The present study} found a negative association between intestinal carriage of B. longum, F. prausnitzii and anthropometric scores of ponderal growth (WAZ and WHZ). Intestinal carriage of B. longum and F. prausnitzii was associated with lower WAZ. Additionally, an increase in the relative abundance of B. longum was associated with increase in WHZ while an increase in the abundance of F. prausnitzii was associated with lower WHZ. To date there is no data on the association between presence or absence of B. longum, F. prausnitzii and ponderal growth in children but data exists on the association between relative abundance of genus Bifidobacterium and WHZ in children. Subramanian et al. found a lower abundance of the genus Bifidobacterium in Bangladeshi children with poor WHZ compared to children with better WHZ168_{. This finding is supported} by data from this study that showed a positive relationship between relative abundance of B. longum and WHZ although the study by Subramanian et al. did not assess the associations at species level.

The negative associations between intestinal carriage of B. longum, F. prausnitzii and WAZ have not been reported before in human studies. This data suggests a potential role of these bacteria in ponderal growth. Murine studies have reported a positive association between the relative abundance of B. longum, D. formicigenerans, F. prausnitzii and weight gain, which is different from the data shown here. The inconsistency between these results suggests that these bacteria might have different effects on ponderal growth in mice and humans.

This study was limited by a number of factors. The use of commercial qPCR kits to describe prevalence of bacterial carriage limited the number of bacterial targets studied as primers and probes for other targets were not commercially available. The lack of standards in the commercial PCR kits precluded absolute quantification of each bacterium. The availability of data for a few demographic

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variables limited the number of possible covariates that could have been considered in the analyses. Data analysis in the present study involved multiple comparisons, which could have had an effect on the interpretation of the results. Benjamini-Hochberg false discovery rate, Bonferroni correction and permutation are some of the methods used to correct for multiple comparisons. Further more refined analysis exploring multivariate models to examine collinearity in explanatory variables and examination of co-variance within the data are also methods by which the effect of individual predictors may be identified.

The use of a published bacterial qPCR assay that allowed relative quantification of each bacteria was one of the strengths of this study. Relative quantification of B. longum had a different relationship with WHZ compared with presence or absence of the bacterium suggesting that the association between B. longum and WHZ is dependent on the abundance and not just the presence of the bacterium. 5.3.4 Conclusion and future work

This study showed high prevalence of F. prausnitzii and D. formicigenerans in fecal samples from rural Malawian children. Carriage of these bacteria was more prevalent in older children compared to younger children. B. longum was found to be the least prevalent bacteria in the fecal samples and its carriage was associated with younger age. These results are consistent with existing data. A. muciniphila, which was present in almost half of the samples, was also shown to be associated with geographic location. Further investigations are needed to understand how the environment affects carriage of A. muciniphila and establish any subsequent effects in the context of EED and child growth. The study also found a relationship between B. longum or D. formicigenerans and biomarkers of EED. The positive relationship between B. longum and biomarkers of EED reported by this study is unusual as B. longum is widely thought of as beneficial to gut health. Therefore, there is need for further research to confirm the existence of such an association in this population. Additionally, future studies might sequence B. longum strains carried by children in this population to establish if there are any genetic differences with the strains that have been identified as beneficial in other populations as such data is lacking. Further studies should investigate if breastfeeding, hygiene, sanitation and other factors

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confound or interact with the relationship between B. longum and biomarkers of EED.

This study also reported negative associations between intestinal carriage of B. longum, D. formicigenerans, F. prausnitzii (identified by qPCR) and ponderal growth in children from low-income settings for the first time. These findings are different from results of experimental studies in mice that indicated a positive association between relative abundance of these 3 bacteria and weight gain. As such, there is need for further studies to validate such associations in children. Future studies could also investigate the effects of absolute bacterial count on ponderal growth compared to presence or absence of a bacterium. Interestingly, this study found a positive association between relative abundance of B. longum and WHZ. This finding supports data reported previously in children from similar low-income settings.

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