# Plant-Derived Phytobiotics as Emerging Alternatives to Antibiotics Against Foodborne Pathogens
## 4 Impact of Phytobiotics on Microbiota of Food and the Intestine
### Impact on Gut Microbiota  
Polyphenols also act as prebiotic-like compounds. Because they are not fully digested in the small intestine, they reach the colon, where they are degraded by the microbiota into simpler phenols and acids, which in turn stimulate the growth of fiber-fermentingbeneficial bacteria [176; 177]. It is important to note that the gut microbiota itself metabolizes flavonoids into active compounds--such as phenolic acids and dihydrohalos--which can inhibit pathogens or exert anti-inflammatory effects in the gut [178]. Thus, a bidirectional interaction exists: polyphenols shape the microbiota, and the microbiota transforms polyphenols, enhancing their bioavailability and bioactivity [76]. In vitro studies have demonstrated that anthocyanins--such as those derived from raspberries, purple potatoes, black rice, or malvidim-3-glucoside from grapes--have a significant impact on the growth of intestinal bacteria. Specifically, these compounds have been shown to stimulate the proliferation of _Bifidobacterium_ spp. and _Lactobacillus_ spp., while concurrently inhibiting the growth of potentially pathogenic bacteria such as _Staphylococcus aureus_ and _Salmonella enterica_ sv. _Typhimuriumium_ during in vitro fermentation experiments [179]. Simultaneously, specific bacterial species have been shown to catalyze the degradation of anthocyanins. For example, _Eubacterium rannulus_ and _Clostridium saccharogumia_ participate in the deglycosylation of cyanidin-3-glucoside--one of the principal anthocyanins--by removing glycosidic residues [180]. The metabolites derived from anthocyanin degradation can further modulate the microbiota. In an animal model, administration of a black raspberry extract rich in anthocyanins restored the abundance of beneficial bacterial species such as _Eubacterium rectale_, _Faecalibacterium prausnitzii_, and _Lactobacillus_ spp., while reducing the overgrowth of pro-inflammatory sulfate-reducing _Desulfoibrio_ spp. and _Enterococcus_ spp. in mice [181]. Significant shifts in the overall gut microbiota composition have also been observed: raspberry anthocyanins altered the proportions of dominant bacterial phyla by increasing the relative abundance of _Frimicutes_ (including _Clostridium_ spp.) and reducing _Bacteroides_ (e.g., _Barnesiella_ spp.) [182]. Moreover, an eight-week supplementation with anthocyanins combined with prebiotic fiber in adults led to beneficial alterations in microbiota composition, marked by an increase in _Bacteroidetes_ and a decrease in _Frimicutes_ and _Actinobacteria_[183]. It is important to highlight that some compounds known primarily for their immunomodulatory effects--such as urolithins--are in fact metabolites produced by the gut microbiota. Urolithins (including several distinct forms) are derived from ellagic acid; for example, ellagitannins are metabolized in humans primarily into urolith A and urolith B [184]. Additionally, urolithins C and D have also been detected in the gastrointestinal tract, indicating that gut bacteria convert ellagic acid into a range of structurally diverse metabolites [185]. This bioconversion occurs mainly in the lower gastrointestinal tract (colon) and is dependent on the presence of a functional gut microbiota. Studies have shown that in individuals consuming ellagitannin-rich extracts from walnuts or pomergranates, bacterial genera such as _Bacteroides_, _Prerotella_, and _Ruminococcus_ dominate the gut microbiota. Furthermore, there is a correlation between the abundance of the _Coriobacteriaceae_ family and the production of urolithins, as well as a concurrent reduction in blood cholesterol levels [186]. Interestingly, different microbial species produce distinct urolithins. For example, _Bifidobacterium_ and _Clostridium_ have been identified as capable of metabolizing pomeramate ellagitannins, with species-specific pathways leading to the formation of different urolithin profiles [187].