No abstract

Strontium-releasing injectable bone cements may have the potential to prevent implant-related infections through the bactericidal action of strontium, while enhancing bone formation in patients suffering from osteoporosis. A meltderived bioactive glass (BG) series (SiO 2 -CaO-CaF 2 -MgO) with 0-50% of calcium substituted with strontium on a molar base were produced. By mixing glass powder, poly(acrylic acid) and water, cements were obtained which can be delivered by injection and set in situ, giving compressive strength of up to 35 MPa. Strontium release was dependent on BG composition with increasing strontium substitution resulting in higher concentrations in the medium. Bactericidal effects were tested on Staphylococcus aureus and Streptococcus faecalis; cell counts were reduced by up to three orders of magnitude over 6 days. Results show that bactericidal action can be increased through BG strontium substitution, allowing for the design of novel antimicrobial and bone enhancing cements for use in vertebroplasty or kyphoplasty for treating osteoporosis-related vertebral compression fractures.

It is common practice to freeze dry probiotic bacteria to improve their shelf life. However, the freeze drying process itself can be detrimental to their viability. The viability of probiotics could be maintained if they are administered within a microbially produced biodegradable polymer - poly-γ-glutamic acid (γ-PGA) - matrix. Although the antifreeze activity of γ-PGA is well known, it has not been used for maintaining the viability of probiotic bacteria during freeze drying. The aim of this study was to test the effect of γ-PGA (produced by B. subtilis natto ATCC 15245) on the viability of probiotic bacteria during freeze drying and to test the toxigenic potential of B. subtilis natto. 10% γ-PGA was found to protect Lactobacillus paracasei significantly better than 10% sucrose, whereas it showed comparable cryoprotectant activity to sucrose when it was used to protect Bifidobacterium breve and Bifidobacterium longum. Although γ-PGA is known to be non-toxic, it is crucial to ascertain the toxigenic potential of its source, B. subtilis natto. Presence of six genes that are known to encode for toxins were investigated: three component hemolysin (hbl D/A), three component non-haemolytic enterotoxin (nheB), B. cereus enterotoxin T (bceT), enterotoxin FM (entFM), sphingomyelinase (sph) and phosphatidylcholine-specific phospholipase (piplc). From our investigations, none of these six genes were present in B. subtilis natto. Moreover, haemolytic and lecithinase activities were found to be absent. Our work contributes a biodegradable polymer from a non-toxic source for the cryoprotection of probiotic bacteria, thus improving their survival during the manufacturing process.

A major hurdle in producing a useful probiotic food product is bacterial survival during storage and ingestion. The aim of this study was to test the effect of γ-PGA immobilisation on the survival of probiotic bacteria when stored in acidic fruit juice. Fruit juices provide an alternative means of probiotic delivery, especially to lactose intolerant individuals. In addition, the survival of γ-PGA-immobilised cells in simulated gastric juice was also assessed. Bifidobacteria strains (Bifidobacteria longum, Bifidobacteria breve), immobilised on 2.5% γ-PGA, survived significantly better (P<0.05) in orange and pomegranate juice for 39 and 11 days respectively, compared to free cells. However, cells survived significantly better (P<0.05) when stored in orange juice compared to pomegranate juice. Moreover, both strains, when protected with 2.5% γ-PGA, survived in simulated gastric juice (pH2.0) with a marginal reduction (<0.47 log CFU/ml) or no significant reduction in viable cells after 4h, whereas free cells died within 2h. In conclusion, this research indicates that γ-PGA can be used to protect Bifidobacteria cells in fruit juice, and could also help improve the survival of cells as they pass through the harsh conditions of the gastrointestinal tract (GIT). Following our previous report on the use of γ-PGA as a cryoprotectant for probiotic bacteria, this research further suggests that γ-PGA could be used to improve probiotic survival during the various stages of preparation, storage and ingestion of probiotic cells.

In this study, a new rapid automated yeast cell counter was assessed. The cell counter (Aber Countstar) uses bright-field microscopy and a dye-exclusion method. This study's aim was to determine whether this method could be effectively employed in an automated slide based counter to assess viability and to compare this method with results from traditional microscopy and from a radio-frequency impedance-based instrument (Aber Compact Lab Yeast Analyser). Excellent correlations were observed between methods. The instrument performed well over a range of yeast concentrations (R 2 = 0.9913 correlation between automated and manual live cell concentrations). Cell diameters compared well with manual recordings. The instrument was also able to track decreasing cell viability in conjunction with the haemocytometer at viabilities over 20%. The radio-frequency impedance based instrument exhibited the smallest deviation between 10 repeats, followed by the cell counter (SD: ± 1.08 × 10 7 ; ± 5.97 × 10 7 , respectively). Manual counts using a haemocytometer exhibited the largest error between repeats (SD: ± 2.63 × 10 8 ) and also required substantially more time (2.28 min) compared with the cell counter (7 sec). The automated cell counter successfully reduced inter-operator errors, a major hindrance with manual analyses. Tests carried out at a brewery in the UK demonstrated that the cell counter provides consistent counts for assorted yeast strains. External tests highlighted the instrument's ease of use and consistency among different strains of brewing yeast and various stages in the brewing process.