Abstract
BackgroundPneumococcal adherence to the nasopharyngeal epithelium is a critical step in colonisation and disease. The probiotic bacterium, Streptococcus salivarius, can inhibit pneumococcal adherence to epithelial cells in vitro. We investigated the mechanism(s) of inhibition using a human pharyngeal epithelial cell line (Detroit 562) following pre-administration of two different strains of S. salivarius.ResultsWhilst the bacteriocin-encoding megaplasmids of S. salivarius strains K12 and M18 were essential to prevent pneumococcal growth on solid media, they were not required to inhibit pneumococcal adherence. Experiments testing S. salivarius K12 and two pneumococcal isolates (serotypes 19F and 6A) showed that inhibition of 19F may involve S. salivarius-mediated blocking of pneumococcal binding sites: a negative correlation was observed between adherence of K12 and 19F, and no inhibition occurred when K12 was prevented from contacting epithelial cells. K12-mediated inhibition of adherence by 6A may involve additional mechanisms, since no correlation was observed between adherence of K12 and 6A, and K12 could inhibit 6A adherence in the absence of cell contact.ConclusionsThese results suggest that S. salivarius employs several mechanisms, including blocking pneumococcal binding sites, to reduce pneumococcal adherence to pharyngeal epithelial cells. These findings extend our understanding of how probiotics may inhibit pneumococcal adherence and could assist with the development of novel strategies to prevent pneumococcal colonisation in the future.Electronic supplementary materialThe online version of this article (doi:10.1186/s12866-016-0843-z) contains supplementary material, which is available to authorized users.
Highlights
Pneumococcal adherence to the nasopharyngeal epithelium is a critical step in colonisation and disease
S. salivarius reduces pneumococcal adherence to pharyngeal epithelial cells Previous studies in our laboratory demonstrated that S. salivarius K12 inhibits pneumococcal adherence to CCL-23 human epithelial cells in vitro, with the strongest effect seen when K12 was added before pneumococci
In this study, we found that various bacteriocin-producing strains of S. salivarius can prevent pneumococcal growth on solid media and that the commercial probiotic strains, K12 and M18, inhibit pneumococcal 6A and 19F adherence to a pharyngeal epithelial cell line
Summary
Pneumococcal adherence to the nasopharyngeal epithelium is a critical step in colonisation and disease. The probiotic bacterium, Streptococcus salivarius, can inhibit pneumococcal adherence to epithelial cells in vitro. We investigated the mechanism(s) of inhibition using a human pharyngeal epithelial cell line (Detroit 562) following pre-administration of two different strains of S. salivarius. PCVs have successfully reduced carriage and disease caused by vaccine serotypes, they are expensive to produce and have led to an increase in colonisation by non-vaccine serotypes (serotype replacement) [3]. There has been increased interest in the use of Manning et al BMC Microbiology (2016) 16:225 probiotics, which are defined as live microorganisms that can confer a health benefit to the host, to reduce pathogen colonisation and respiratory tract infections [4]. Proposed mechanisms of probiotic action include inhibition of pathogen colonisation via competition for binding, direct inhibition due to the activity of secreted antimicrobial molecules and the induction of immunomodulatory effects in the host [5,6,7,8,9]
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