**6. Role of probiotics as antiviral**

A number of microorganisms have been found in the human respiratory tract as the primary source of the respiratory virus. We may reduce the occurrence of disease development in humans by limiting the penetration of respiratory tract viruses into the membranes of mucosal epithelial cells. The human body contains a diverse community of mutually advantageous commensal bacteria known as microbiota [49]. Probiotics are microorganisms that have potential health benefits when eaten in a specific amount. There are two basic types of probiotics: Lactobacillus and Bifidobacterium and Both have a positive impact on human health since it acts as an antiviral agent, lowering the binding ability of viruses to the host receptor and thereby capturing the virus. Probiotics administering protects individuals from various respiratory viral infections like Respiratory syncytial virus, SARS-CoV-2, Influenza A virus. This antiviral activity was investigated by the strain's specificity as well as the host immune status [50].

*L. casei shirota* (LcS) is a lactobacillus probiotic strain isolated from the oral microbiota. It has been stated that when Lcs was presented to influenza (H1N1) infected mice, the viral titer declined. Furthermore, LcS stimulates the innate or nonspecific immune system by increasing the production of antiviral cytokines like IFN-α. Another study discovered immunomodulatory activity against Respiratory syncytial virus. LcS, on the other hand, has shown negligible findings into clinical trials, especially among older community, when compared to the control group [51]. Clinical trials were conducted on *L. Casei* (DN-114,001) demonstrated substantial antiviral activity in separate studies in infants, adults, and the elderly. It decreases the clinical signs and symptoms of respiratory tract infection in infants, adults, and the elderly [52].

*L. fermentum* is a bacteria present in both people and animals microbiota and is commonly used it as a probiotic in people. This probiotic was tested in clinical studies, specifically in children and young adults, as well as lab animals to examine the process of viral prevention toward respiratory infections. The efficacy of *L. fermentum* CJL-112 and *L. fermentum*-1 have been studied against Influenza virus (H1N1) infected with mice and the findings indicate a marked decline in viral count, with significant stimulation of IL-12 and Immunoglobulin (IgA) development, allowing for an improvement in mouse longevity. The combined effect of probiotic (*L. fermentum* CECT5716) and prebiotic (galacto-oligosaccharides) had assessed in healthy infants, and this research showed a significant decrease in the incidence of urinary and respiratory tract illness [53].

*L. acidophilus* is a well-known lactic acid bacteria strain that is used in medicinal treatments. Since *L. acidophilus* is commonly used to treat gastrointestinal issues, just few researchers have examined into its antiviral activity. *L. acidophilus* L-92, retrieved from a healthy Japanese citizen, demonstrated antiviral activity against influenza virus through IFN-α and natural killer cell modulation. The antiviral activity of *L. brevis* KB-290 against H1NI was examined, and virus levels were found to be depleted as a result of IgA and IFN-α stimulation [54]. Bifidobacteria aids in digestion, immunity, and the prevention of almost all gastrointestinal infections. These strains have been used in several clinical studies against viral respiratory diseases to determine the mechanism of antiviral effect [55].

*B. longum* (BB536) demonstrated anti-H1N1 activity in mice after parenteral route for two weeks prior to disease, owing to a decrease in IL-6 and IFN production. Moreover, this probiotic strain exhibited the potential to dramatically reduce the clinical signs and symptom. The combination of *B. animalis ssp. Lactis and L. reuteri* indicated the strongest antiviral activity against respiratory system microbes. *L. rhamnosus* GG is the most extensively researched probiotic, with substantial reductions in diarrhea length and rotavirus pathogenicity [56].

The COVID-19 disease affects the lungs and the gastrointestinal tract, inducing pro-inflammatory Th1-cells to release various cytokines such as TNF-alpha leading to the establishment of the cytokine storm. Dysregulation in the intestinal microbiome contributes to an imbalance of Th1 and Th2, which stimulates the formation of pro-inflammatory cytokines and, eventually, a cytokine storm in epithelial cells in the lungs [57]. Probiotics promote the proliferation of "beneficial bacteria" in the intestine, resulting in a change in the stability of Th1/Th2 cells, which lowers the cytokine storm and the severity of infections. It was recently found that using probiotic bacteria derived from Lactobacillus and Bifidobacterium improves the chance of healing from COVID-19 patients. *L. paracasei* and *L. coryniformis* has the ability to bind angiotensin converting enzyme type 2, which is a receptor needed by the SARS-CoV-2 virus for attachment, preventing its entrance into cell and thereby decrease the possibility of COVID-19 infection [58].

#### **7. Role of probiotics as antifungal**

The global fungal load is extremely high, and it is expected to rise even higher as the proportion of immunocompromised people rises. In contrast, the drugs used to treat fungal pollutions are extremely small, and some of them are extremely dangerous. *Candida gullemondii*, *C. auris, C. glabrata,* Aspergillus and Fusarium species are evolving as impervious and hazardous fungal pathogens. These species are responsible for 5–10% of global food spoilage [59].

Aflatoxin is an extremely hepatotoxic bioactive compound produced by fungi, which is a major global concern. A toxin-free feed is demanded by the existing agriculture and livestock production industries. Use of such microbes to food preservation has grown in popularity in recent years, owing to customer needs for less reliance on chemical preservatives. Lactic acid bacteria are widely regarded as a "beneficial organism," that is used to avoid contamination of food and feed, as well as to chemically store food. It is also intended to produce antimicrobial agents [60].

*L. fermentum* L23 and *L. rhamnosus* L60 produced bioactive compounds such as hydrolytic enzymes, organic acids, bacteriocins, and hydrogen peroxide and blocked the fungal growth of most all aflatoxigenic strains. L60 has decreased Aflatoxin B1 output by greater than 90 percent and L23 by up to 100 percent. As a result, L23 and L60 have been used to properly manage aflatoxigenic fungi in livestock feed [61].

Probiotics have been shown to decrease *C. albicans* infections in a variety of body organ systems and are widely regarded as important for good health. Probiotics, for example, can treat gastroenteritis, dairy allergy, and the signs and symptoms of irritable bowel syndrome. *C. albicans* has been assigned two virulent functions: filamentation and biofilm growth. We can minimize both of these virulent functions through using probiotics. The yeast form of candida is more readily phagocytized than the hyphal form, and probiotics help the host organism combat pathogens by preventing filamentation. However, the exact mechanisms by which fungal infections are prevented are unknown [62].

#### **8. Conclusion**

Nowadays, the discovery of the use of probiotic strains has improved our understanding of the relationship between diet and people's health. Probiotics boost *The Immunomodulatory Role of Probiotics DOI: http://dx.doi.org/10.5772/intechopen.98839*

innate and humoral immunity against pathogens. Probiotic bacteria bind to gut epithelial cells and release cytokines (IFN-γ) and interleukins (IL-10) that establish a microclimate in the tracheae, bronchi, and reproductive organs and gut lamina propria, triggering clonal proliferation of B cells to make IgA and activating Treg cells, thereby maintaining immune balance in the gastrointestinal tract. COVID-19 is a newly emerging virus that causes deadly disease all over the world. Probiotic strains, especially lactobacillus species therapy, may be critical in controlling COVID-19, and probiotic treatment may be considered as a choice for the reduction and mitigation of COVID-19 infection globally.
