Heat-killed lactobacilli alter both microbiota composition and behaviour.

Recently it has been proposed to expand the definition of psychobiotics (beneficial bacteria (probiotics) or support for such bacteria (prebiotics) that positively impact mental health) to any exogenous influence whose effect on the brain is bacterially-mediated. This definition would include inactivated microorganisms with anxiolytic and antidepressant effects. The use of inactivated microorganisms has several advantages over living organisms, including no risk of infection in vulnerable individuals and ease of use in terms of storage and delivery options. It has been reported that consumption of inactivated microorganisms can affect behaviour, particularly in chronic or prolonged stress situations, but effects on healthy populations have not been investigated to the same extent. Also, only limited data is available on the effects of inactivated microorganisms on the microbiota of healthy individuals (animal or human). Therefore, we investigated the effect of feeding a standard mouse chow which incorporates ADR-159, a heat-killed fermentate generated by two Lactobacillus strains, on the behaviour and microbiota of healthy mice. Prolonged consumption of ADR-159 diet had no adverse effect on anthropometrics or general health, but the ADR-159 fed animals demonstrated increased sociability and lower baseline corticosterone levels (stress hormone). The diet also led to subtle but significant changes in the microbiota, with less abundant taxa being most affected. The behavioural, biochemical and microbiological results provide a new light on the impact of inactivated microorganisms and their metabolites on the social behaviour and microbiota of healthy mice.

Design and characterisation of a dissolving microneedle patch for intradermal vaccination with heat-inactivated bacteria: A proof of concept study.

This work describes the formulation and evaluation of dissolving microneedle patches (MNs) for intradermal delivery of heat-inactivated bacteria. Pseudomonas aeruginosa, strain PA01, was used as a model bacterium. Utilising a simple, cost effective fabrication process, P. aeruginosa was heat-inactivated and formulated into dissolving MNs, fabricated from aqueous blends of 20% w/w poly(methylvinylether/maleic acid). The resultant MNs were of sufficient mechanical strength to consistently penetrate a validated skin model Parafilm M®, inserting to a depth of between 254 and 381 µm. MNs were successfully inserted into murine skin and partially dissolved. Analysis of MN dissolution kinetics in murine ears via optical coherence tomography showed almost complete MN dissolution 5 min post-insertion. Mice were vaccinated using these optimised MNs by application of one MN to the dorsal surface of each ear (5 min). Mice were subsequently challenged intranasally (24 h) with a live culture of P. aeruginosa (2 × 106 colony forming units). Bacterial load in the lungs of mice vaccinated with P. aeruginosa MNs was significantly (p = 0.0059) lower than those of their unvaccinated counterparts. This proof of concept work demonstrates the potential of dissolving MNs for intradermal vaccination with heat-inactivated bacteria. MNs may be a cost effective, potentially viable delivery system, which could easily be implemented in developing countries, allowing a rapid and simplified approach to vaccinating against a specific pathogen.

In vitro and in vivo anti-microbial activity evaluation of inactivated cells of Lactobacillus salivarius CECT 5713 against Streptococcus mutans.

OBJECTIVE: Defining the etiology of dental caries is a complex problem. The microbiological approach has included Streptococcus mutans as one of the bacterial species involved in this disease. This research investigates the inhibitory effects of heat-inactivated Lactobacillus salivarius CECT 5713 against S. mutans using in vitro and in vivo assays. DESIGN: On the one hand, the effect of non-viable L. salivarius CECT 5713 on the in vitro adhesion of S. mutans to hydroxyapatite discs was evaluated. On the other hand, levels of Streptococcus mutans, amount of salivary flow and salivary pH before and after taking the rinse with the non-viable L. salivarius CECT 5713 in healthy volunteers were assessed (self-controlled open-label pilot study). RESULTS: The levels of S. mutans seemed to decrease in the in vitro and in vivo assays (p<0.05). The in vitro effect of non-viable L. salivarius was maintained until 36 months of storage. In addition, the reduction of S. mutans salivary concentration in the volunteers was statistically significant from the third day until two weeks of treatment. CONCLUSIONS: Heat-inactivated L. salivarius CECT 5713 prevents S. mutans adhesion to hydroxyapatite and could be used as a strategy to reduce the salivary concentration of this oral pathogen.