Lacticaseibacillus rhamnosus GG inhibits infection of human keratinocytes by Staphylococcus aureus through mechanisms involving cell surface molecules and pH reduction

Abstract

Beneficial bacteria represent an emerging tool against topical diseases, including infection caused by Staphylococcus aureus. Here, we investigated several anti-pathogenic mechanisms of the model probiotic Lacticaseibacillus rhamnosus GG against a clinical S. aureus isolate by implementing various mutants lacking important cell surface molecules. We analysed adhesion of L. rhamnosus and competitive adhesion with S. aureus to primary human keratinocytes, L. rhamnosus and S. aureus auto- and co-aggregation, S. aureus growth inhibition, keratinocyte viability increase, and monocyte Toll-like receptor (TLR) activation by L. rhamnosus as such, or with S. aureus. L. rhamnosus mutated in SpaCBA pili exhibited reduced adhesion to keratinocytes, reduced ability to prevent S. aureus adhesion to keratinocytes and reduced co-aggregation with S. aureus. Mutants in cell wall exopolysaccharides showed enhanced adhesion to keratinocytes and TLR activation in monocytes, suggesting involvement of additional cell surface molecules masked by exopolysaccharides. All L. rhamnosus strains inhibited S. aureus growth, likely due to acidification of the medium. Live (but not UV-inactivated) L. rhamnosus significantly reduced inflammatory TLR activation in monocytes by S. aureus. These data suggest the key role of SpaCBA pili and additional contribution of other cell surface molecules as well as secreted components of L. rhamnosus GG in the multifactorial inhibition of S. aureus adhesion and toxicity in the skin niche.

Lactic acid bacteria as probiotics for the nose?

“…For instance, in the model strain Lactocaseibacillus rhamnosus GG, SpaCBA pili have been described that mediate adhesion to intestinal mucus and epithelial cells (Kankainen et al, 2009). Recently, we also demonstrated that these pili are one of the key factors promoting its adhesion to human epithelial keratinocytes and interfering with adhesion of S. aureus (Spacova et al, 2020a(Spacova et al, ,2020b showing that the SpaCBA pili are adaptation factors in other body sites than the gut. For the URT, relatively good adherence of L. rhamnosus GG to the respiratory epithelial cell line Calu-3 and nasal epithelial cells of patients and healthy controls was observed ).…”

“…For CRS in particular, the EPOS2020 (European Position Paper on Rhinosinusitis and Nasal Polyps) steering group recently concluded, based on the small studies with limited sample sizes that are conducted up to now, that there is currently no evidence for the use of oral or topical URT probiotics as treatment option for CRS patients (Fokkens et al, 2020). It should be noted however that analysing probiotic interventions is highly challenging, and sweeping generalizations on their efficacy based on this limited amount of available studies is difficult, as also mentioned by the EPOS2020 steering group, considering the probiotic strain-specificity and multifactorial mechanisms of action that furthermore depend on the application site (Spacova et al, 2020a(Spacova et al, ,2020b. Such screenings for probiotic efficacy and safety demands a dedicated pipeline, where a combination of in silico, in vitro and in vivo models are advised.…”

“…Traditional in vitro screening methods are the first step to evaluate the probiotic efficacy and safety (Irina Spacova et al, 2020a,2020b. In addition, whole-genome sequencing of probiotic candidate strains followed by detailed in silico analysis at gene level can detect potential probiotic and adaptation factors, as well as virulence and antibiotic resistance genes (Salvetti et al, 2016).…”

Bacteria autoaggregation: how and why bacteria stick together

“…Adhesins, particularly short ones like integral outer membrane proteins and autotransporters can be masked or shielded by exopolysaccharides (EPS), fimbriae and even secreted proteins [ 23 , 35–38 , 39 19]. In Lacticaseibacillus rhamnosus , EPS production masked adherence by spaCBA pili [ 38 ] and encapsulated Pasteurella multocida cells autoaggregated less than non-encapsulated (capsule-deficient) P. multocida [ 40 ]. Capsule interference could be due to its electrostatic negative charge [ 40 ] or sterical obstruction of autoaggregation factors [ 41 ].…”

“…Probiotic organisms often protect against infection by autoaggregating or coaggregating with pathogens. Autoaggregation allows competitive exclusion and displacement of pathogens while coaggregation increases proximity of the co-aggregating probiotic bacteria's Type VI secretion systems and releases antimicrobial substance to the target pathogen [ 38 ]. The well-documented probiotic potential of Lacticaseibacillus rhamnosus GG lies in its immunogenic SpaCBA pili that mediate mucosal adherence and autoaggregation [ 70 ].…”