Page 31 - Read Online

Horie et al. Microbiome Res Rep 2024;3:35 https://dx.doi.org/10.20517/mrr.2024.08 Page 9 of 12

Bacteroidota and Actinomycetota were more prevalent in the fecal microbiota of cats. Additionally, in the
intestinal flora of dogs fed a 5% chicken liver and heart hydrolysate plus 20% chicken meal diet instead of a
25% chicken meal diet, fecal microbiota was shifted to higher abundance in Ruminococcus gauvreauii group
[55]
as well as lower Clostridium sensu stricto, Sutterella, Fusobacterium, and Bacteroides . These results suggest
that proteins influence the composition of Paeniclostridium and Fusobacterium in the intestinal flora. Fish-
based diets predominantly consist of animal protein, but fecal flora and isolated lactic acid bacteria of
piscivorous animals were different from those of carnivorous animals. The factors that determine the
intestinal flora of piscivorous animals are still unknown. Analysis of gut microbiota composition in raccoon
dogs fed three different diet types (fish and amphibians, mixed protein with maize, and solely maize)
exhibited notable variations in the relative abundances of Bacteroidota, Proteobacteria, and
Verrucomicrobiota depending on the dietary composition. On the other hand, Bacillota remained the most
dominant phylum regardless of feeding habits. Racoon dogs solely fed maize exhibited a significant increase
[56]
in Proteobacteria, potentially linked to dietary fiber and lignin degradation .

The selective pressure acting on the different types of lactic acid bacteria related to the host feeding habits
has yet to be clarified. It has been reported that protease activity was high in the fermented liquid of
L. salivarius, which was found in many carnivorous animals in this study . L. salivarius may be compatible
[57]
with carnivores.

Another possibility is the variety of sugar utilization by these bacteria. Herbivore-derived Lactobacillus
strains tended to rely on more types of sugar than carnivore-derived strains. For example, L. equi isolated
from the horse could use arabinose, rhamnose, and inulin, which are found in plants. In herbivores, plant-
derived polysaccharides may be degraded by other bacteria, and Lactobacillus spp., which can use a wide
variety of sugars, may be predominant. As an example, genomic analysis of carbohydrate-active enzymes
suggested that porcine-derived L. johnsonii was capable of utilizing a wide range of carbohydrates .
[58]
However, the origin of lactic acid bacteria living in the intestinal tract and the mechanisms by which they
colonize the intestine deserve attention in the future. Nutrient of diet is important for the selection of lactic
acid bacteria species. In this study, only the sugar utilization of isolated lactic acid bacteria was investigated.
Meat is rich in protein, while fish is abundant in docosahexaenoic acid and eicosapentaenoic acid. To
understand why dietary habits exert greater influence on dominant lactic acid bacteria than host species, it
is essential to investigate whether these amino acids and fatty acids impact the metabolism and growth of
lactic acid bacteria.

Although many types of herbivores were included in the present study, a bias existed in the selection of
carnivores. Except for the polar bear, all carnivores included in this study belong to the family Felidae. In
this study, we were able to find basic trends in the distribution of intestinal lactic acid bacteria, but the
number of samples was insufficient for a complete picture. Thus, other carnivorous families, such as weasel,
hyena, wolf, and fox, should be investigated. In addition, herbivores such as ruminant animals may have
different Lactobacillus species coexisting in their intestinal tracts that warrant further investigation. In
ruminants, metabolism by microorganisms occurs in the rumen; thus, food is digested differently when it
reaches the intestinal tract, which could affect the lactic acid bacteria in the flora. In the present study,
Lactobacillus species were neither found in, nor determined by, 16S rRNA gene amplicon sequencing of the
feces of giraffe, a ruminant animal.

Considering the above results, we suggest that the selection of lactic acid bacteria strains used as probiotics
should depend on their suitability for the host animals. For example, L. salivarius and L. saerimneri may be
more effective probiotics than L. equi in feline carnivores. The administration of L. equi to carnivores may