Berry phenolics selectively inhibit the growth of intestinal pathogens

AIMS

To investigate the effects of berries and berry phenolics on pathogenic intestinal bacteria and to identify single phenolic compounds being responsible for antimicrobial activity.

METHODS AND RESULTS

Antimicrobial activity of eight Nordic berries and their phenolic extracts and purified phenolic fractions were measured against eight selected human pathogens. Pathogenic bacterial strains, both Gram-positive and Gram-negative, were selectively inhibited by bioactive berry compounds. Cloudberry and raspberry were the best inhibitors, and Staphylococcus and Salmonella the most sensitive bacteria. Phenolic compounds, especially ellagitannins, were strong inhibitory compounds against Staphylococcus bacteria. Salmonella bacteria were only partly inhibited by the berry phenolics, and most of the inhibition seemed to originate from other compounds, such as organic acids. Listeria strains were not affected by berry compounds, with the exception of cranberry. Phenolic compounds affect the bacteria in different mechanisms.

CONCLUSIONS

Berries and their phenolics selectively inhibit the growth of human pathogenic bacteria.

SIGNIFICANCE AND IMPACT OF THE STUDY

Antimicrobial properties of berries could be utilized in functional foods. Furthermore these compounds would be of high interest for further evaluation of their properties as natural antimicrobial agents for food and pharmaceutical industry.

Stationary-phase acid and heat treatments for improvement of the viability of probiotic lactobacilli and bifidobacteria

AIMS

To investigate whether sublethal treatments of stationary-phase probiotic cultures enhance their survival during lethal treatments and to adapt these treatments to the fermenter-scale production of probiotic cultures.

METHODS AND RESULTS

Conditions for acid and heat pretreatments were screened for three Lactobacillus and two Bifidobacterium strains. Strains were sublethally treated both at laboratory scale and at fermenter scale in a strain-specific manner and exposed to a subsequent lethal treatment. At laboratory scale viability improvement was detected in each strain. However, improvement was more pronounced in the Lactobacillus than in the Bifidobacterium strains. At fermenter scale three strains were tested: for the two Lactobacillus strains a marked improvement in viability was obtained whereas for the Bifidobacterium strain the improvement was either minor or not detected.

CONCLUSIONS

Development of treatments for viability enhancement of probiotic strains is feasible, but strain-specific optimization is necessary to obtain notable improvements.

SIGNIFICANCE AND IMPACT OF THE STUDY

Strain-specific treatments were developed for the viability enhancement of stationary-phase probiotic cells both at laboratory and fermenter scale. These results can be utilised in the production of probiotic cultures with improved viability.

Antimicrobial properties of phenolic compounds from berries

AIMS

To investigate the antimicrobial properties of phenolic compounds present in Finnish berries against probiotic bacteria and other intestinal bacteria, including pathogenic species.

METHODS AND RESULTS

Antimicrobial activity of pure phenolic compounds representing flavonoids and phenolic acids, and eight extracts from common Finnish berries, was measured against selected Gram-positive and Gram-negative bacterial species, including probiotic bacteria and the intestinal pathogen Salmonella. Antimicrobial activity was screened by an agar diffusion method and bacterial growth was measured in liquid culture as a more accurate assay. Myricetin inhibited the growth of all lactic acid bacteria derived from the human gastrointestinal tract flora but it did not affect the Salmonella strain. In general, berry extracts inhibited the growth of Gram-negative but not Gram-positive bacteria. These variations may reflect differences in cell surface structures between Gram-negative and Gram-positive bacteria. Cloudberry, raspberry and strawberry extracts were strong inhibitors of Salmonella. Sea buckthorn berry and blackcurrant showed the least activity against Gram-negative bacteria.

CONCLUSION

Different bacterial species exhibit different sensitivities towards phenolics.

SIGNIFICANCE AND IMPACT OF THE STUDY

These properties can be utilized in functional food development and in food preservative purposes.

Ultrastructure of a Bacillus sp. strain KL8 isolated from indoor dust

A motile Gram-positive bacterial strain (KL8) was isolated from indoor dust. It was identified by API-test50 CHB as a species of Bacillus. This Bacillus sp. strain KL8 was described using different electron microscopic techniques: negative staining, thin sectioning, metal shadowing and freeze-etching. An additional surface layer (S-layer) was the outermost layer of the cell wall of this flagellated bacterium. The hexagonally arranged protein lattice covering the cells had a lattice constant about 9-10 nm, which falls in the same range as that of Bacillus anthracis.