Colonization and persistence of S.salivarius 24 SMBc in human rhinopharynx

Much attention has recently been devoted to the analysis of the oral microbiota to develop a bacteriotherapy focused on prevention and/or treatment of upper respiratory tract infections. The oral cavity harbours some beneficial bacterial species such as Streptococcus salivarius which is considered the predominant 'safe' colonizer, capable of fostering more balanced, health-associated oral microflora, interfering with potential pathogens. This antagonist activity is often mediated by competition for nutriments, better adhesion to target cells and release of bioactive agents such as bacteriocins. [1-2] In our laboratory, we characterized one strain of S.salivarius 24SMB, isolated from healthy children, as a potential oral probiotic for its characteristics: i) safety for the host, ii) potent capacity of adhesion to HEp-2 cells and iii) excellent inhibitory activity against S.pneumoniae and S.pyogenes. In this study, we evaluated the safety and ability of S.salivarius 24 SMB to colonize and persist in the upper respiratory tract by a clinical trial protocol conducted on healthy adult volunteers. Material and methods The study enrolled 17 patients: the nasal spray formulation of S.salivarius 24 SMB was given for 3 days after azithromycin treatment and the presence of S.salivarius 24 SMB in rhinopharynx tissue was determined after 2/4/24 h, and 7 days from nasal administration. The nasal swabs for each time were plated onto MSA, a selective medium for streptococci, used for differentiation of the viridans strains. Cultures were incubated overnight at 37°C in 5% CO2 in air. The presence of our strain was determined by molecular identification, antagonism tests to evaluate BLIS production and RAPD-PCR to distinguish the S.salivarius 24 SMB genotype from other S.salivarius strains. ResultsOur results were obtained by analysis of each a-haemolitic streptococci isolated on MSA using antagonism tests to evaluate BLIS production and RAPD-PCR to distinguish S.salivarius 24 SMB’s genotype from other S.salivarius strains. This study demonstrated: i) the absence of adverse effects for all subjects enrolled, and ii) the capability of S. salivarius 24 SMB to persist in rhinopharynx tissue in 50% of subjects after 7 days from the last dose of the formulation (105 CFU/mL). Only one patient was colonized by S.salivarius 24 SMB and another by S.salivarius Today there are some candidate probiotic strains based on the species S.salivarius that have been proposed to control microbial upper respiratory tract diseases. However, there is still only relatively limited clinical evidence on oral probiotics. In this study, we demonstrated that the use of S.salivarius 24 SMB by nasal spray was well tolerated in all patients and this strain was able to colonize the rhinopharynx making it suitable for use in bacteriotherapy.For these peculiar characteristics of S.salivarius 24 SMB this strain was involved in a randomized double blind trial to prevent and/or treat chronic otitis media in pediatric age patients. The statistical analysis and final evaluation of this study are ongoing.