Table 1.

Clinical outcome of using probiotic bacterial strains for viral respiratory infections.

Bacterial strain	Viral respiratory infection	Outcome	Reference
Lactobacillus GG (LGG)	Respiratory tract infections	The study assessed the performance of LGG in the restriction of respiratory tract diseases in children attending daycare centers. Their results indicated that LGG treatment could be advised as a valid means of reducing the risk of upper respiratory tract diseases in children attending daycare centers.	[75]
Lactobacillus paracasei N1115	Upper respiratory tract infections (URTI)	The investigation was to evaluate whether yogurt enriched with a probiotic strain could benefit middle-aged and older adults suffering from severe URTIs in a randomized, blank-controlled, parallel-group trial. The study results recommended that yogurt with chosen probiotic strains such as N1115 may diminish the risk of severe upper tract diseases in the elderly. The augmentation of T-cell-mediated immune protection might be one of the critical underlying mechanisms by which probiotics help to alleviate infections.	[149]
Haemophilus influenzae, Streptococcus, Corynebacterium, Moraxella, Staphylococcus aureus	Respiratory syncytial virus (RSV)	The study assessed whether specific nasopharyngeal microbiota are correlated with distinct host transcriptomic profiles and infection severity in children infected with RSV. The study results showed that the interplay between RSV and nasopharyngeal microbiota might temper host immune responses, possibly altering the clinical severity of the disease.	[36]
Lactobacillus rhamnosus GG	Respiratory tract infections	The study hypothesized that early prebiotic or probiotic supplementation could decrease the risk of virus-associated RTIs throughout the first year of life in a cohort study on preterm infants. The results demonstrated that altering gut microbiota with specific prebiotics and probiotics might represent a novel and cost-effective approach to decreasing the risk of rhinovirus infections.	[113]
Lactobacillus rhamnosus GG	Respiratory illness	This study showed that long-term daily use of milk containing Lactobacillus rhamnosus GG decreased the rate of respiratory illnesses in children attending daycare centers (those who finished the treatment course, and not the whole population).	[90]
Lactobacillus rhamnosus GG	Respiratory tract infection	In this randomized, double-blinded, placebo-controlled 28-week intervention, nasopharyngeal swab specimens were obtained from children suffering from respiratory infections who were given normal milk (N = 97) or the same milk enriched with the probiotic Lactobacillus rhamnosus GG (N = 97). This study showed that children taking Lactobacillus rhamnosus GG had a shorter time with respiratory manifestations than children in the control group. However, probiotic treatment did not decrease the amount of viral shedding or the severity of respiratory signs.	[93]
Lactobacillus casei rhamnosus	Respiratory tract infection	This study examined the treatment and prevention performance of three commercial probiotic products on pediatric infectious diseases in a double-blind, randomized, controlled trial. This investigation showed that L. casei could alleviate bacterial, viral, and respiratory infections.	[106]
Bifidobacterium lactis subs plactis Bl-04 Lactobacillus acidophilus NCFM Bifidobacterium animalis subsp. Lactis Bi-07	Respiratory tract infection	This study aimed to examine the effect of supplementation with probiotics on respiratory and gastrointestinal disorders in healthy working men and women. This study indicated that the Bl-04 probiotic taken as a nutritional supplement was beneficial for decreasing the risk of URTI in healthy, physically active adults.	[201]
Lactobacillus gasseri PA 16/8, Bifidobacterium longum SP 07/3, B. bifidum MF 20/5	Common cold	This study evaluated the effects of using L. gasseri PA 16/8, B. longum SP 07/3, and B. bifidum MF 20/5 (5 × 107) cfu/tablet) for at least three months on the severity of manifestations and the frequency and duration of the common cold. This study showed that the intake of probiotic bacteria for at least three months significantly decreased the duration by approximately two days and diminished the severity of manifestations.	[38]
Lactobacillus fermentum (CECT5716)	Influenza	The co-adjuvant capacity of the oral administration of the breast-milk-isolated strain Lactobacillus fermentum (CECT5716) with an anti-influenza vaccine was evaluated. This study demonstrated that oral treatment with L. fermentum CECT5716 potentiates the immunologic responses to the anti-influenza vaccine and may enhance protection by boosting the T-helper type 1 response and eliciting the virus-neutralizing antibodies.	[135]
Lactobacillus casei DN-114 001	Respiratory tract infection	The study investigated the ability of a dairy product containing the probiotic strain Lactobacillus casei DN-114 001 to protect independently-living elderly individuals against widespread infectious diseases. The results showed that the consumption of the probiotic was correlated with a reduced duration of routine infectious disorders, particularly URTIs such as rhinopharyngitis, compared with a control group.	[63]
Lactobacillus bulgaricus OLL1073R-1	Respiratory tract infection	This study evaluated whether the consumption of yogurt fermented with Lactobacillus delbrueckii ssp. bulgaricus OLL1073R-1 had a protective effect against the common cold. The results showed that the consumption of yoghurt fermented with L. bulgaricus OLL1073R-1 increased natural killer cell activity and reduced the risk of catching a common cold in the elderly.	[119]
Porphyromonas spp., Granulicatella spp., Fusobacterium spp., Lachnospiraceae spp., Haemophilus spp.	Influenza	This study evaluated whether precise bacterial community structures in the nasopharynx of children during hospitalization are correlated with various clinical consequences of influenza. The results showed that the expanded bacterial diversity in the nasopharynx of children was considerably correlated with influenza severity. Patients with severe influenza showed a reduced relative frequency of S. aureus and increased abundance of Prevotella, Streptobacillus, Porphyromonas, Granulicatella, Veillonella, Fusobacterium, and Haemophilus in their nasopharynx. This suggests the potential application of microbial signatures as prognostic biomarkers of influenza outcome.	[96]