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

Administration of a cocktail of lactic acid bacteria consisting of Lactobacillus crispatus JB/SL-10,
Limosilactobacillus oris JB/SL-20, L. reuteri JB/SL-25, Lactobacillus johnsonii (L. johnsonii) JB/SL-39, and
Ligilactobacillus salivarius (L. salivarius) JB/SL-43 improved common enteric disease caused by Clostridium
[26]
perfringens in chickens by improving intestinal morphology and modulating innate immune responses .
Although these studies were aimed at improving livestock productivity, they show that select lactic acid
bacteria used as probiotics are also effective in livestock.

On the contrary, there are typically 500 to 1,000 species of bacteria residing in the intestinal tract,
10
12
collectively forming the intestinal flora. In the gastrointestinal tract, there are approximately 10 -10 cells/g
of bacteria inhabiting the large intestine [3,27] . Nevertheless, the diversity and abundance of bacteria in the
intestine may vary depending on the study. The intestinal flora is intricately linked to the health condition
of the host, being influenced by the host’s physiological state.

In recent years, biologists have accumulated evidence for a close relationship between host health and
intestinal flora. The intestinal microbiota is affected by the physical condition of the host; for instance,
individuals with obesity have a high proportion of Bacillota bacteria. In addition, the intestinal microbiota
of individuals without obesity contains a larger proportion of Bacteroidota bacteria than that of individuals
with obesity [28-32] . The different compositions of these intestinal microbiota can be ascribed to the fact that
[33]
Bacillota bacteria are energy-efficient and can use sugars in foods that humans cannot digest . Diet is the
most prominent factor affecting the composition of the intestinal microbiota, including the presence of
Lactobacillaceae [34,35] . Consuming an animal or plant diet causes changes to the intestinal microbiota that
activate the immune system and induce inflammation [36,37] . Diets high in saturated fat and animal proteins,
such as Western diets, increase the population of Bacteroides in the gut, whereas diets high in dietary fiber
and carbohydrates increase the population of Prevotella . However, individual fixed intestinal flora species
[38]
fluctuate as a result of short-term dietary changes and general antibiotics .
[39]
As mentioned earlier, the composition of the intestinal flora varies between individuals consuming animal-
based and plant-based diets. When lactic acid bacteria are consumed as probiotics, they do not work in
isolation but are believed to influence the existing intestinal flora. This interaction with the intestinal flora is
considered one of the key effects of probiotics. However, if inappropriate bacterial species are introduced,
they may not survive in the intestinal tract and could prove ineffective as probiotics. Therefore, to optimize
the efficacy of lactic acid bacteria as probiotics, it is crucial to combine them with bacterial species naturally
present in the intestinal flora. While research on the intestinal flora of humans and laboratory animals,
primarily rodents, as well as livestock like pigs, cows, and sheep, is advancing, there is limited knowledge
regarding zoo animals.

To maintain the health of zoo animals, lactic acid bacteria supplements are sometimes administered.
However, it’s uncertain whether the selected strains are suitable for the host animals. Analysis of the gut
microbiota in insectivorous bats, Nyctalus noctula (N. noctula) and Vespertilio murinus (V. murinus), and
frugivorous bats, Carollia perspicillata, revealed notable differences in microbial diversity between the two
dietary groups. Conversely, the disparities between N. noctula and V. murinus were less pronounced. These
findings indicate that the gut microbiota of bats is not strictly species-specific but rather influenced by
dietary preferences .
[40]

Choosing the optimal lactic acid bacteria that harmonize with the intestinal flora based on dietary habits is
crucial for the health and welfare of zoo animals. Hence, this study aimed to explore the varieties of lactic
acid bacteria and the intestinal flora in three common feeding habits among zoo animals: carnivorous,
herbivorous, and piscivorous.