Antibiotic susceptibility of deoxyribonuclease-positive enterococci isolated from milk and milk products and their epidemiological significance

Cholesterol-lowering effects and safety assessment of Lactobacillus spp. in vivo and in vitro testing for human use as probiotic from the dairy product in Egypt

BACKGROUND

The toxicity profile of lactobacilli may be strain dependent, so it should be considered for safe utilization of probiotics. Further, in vivo studies are necessary to evaluate their safety.

RESULT

The ability of various probiotic strains to hydrolyze bile salts has been confirmed without noticeable hemolytic activity. Results revealed the presence of α-glucosidase, β-glucosidase, α-galactosidase, and β-galactosidase activity in all investigated isolates, while none of the isolates produced the carcinogenic enzyme β-glucuronidase. The probiotic strains exhibited remarkable cholesterol-lowering impact. Also, we found no evidence of chronic toxicity under the experimental conditions based on gross pathological examination of the viscera and study of the spleen and liver weight ratios. These findings indicated that the investigated strains, either alone or combined with their metabolites, had no obvious adverse effect on the mice's general health status.

CONCLUSION

There is prove that the investigated probiotic strains are safe to be utilized for enhancing of the growth performance and are free of adverse side effects.

Antifungal activity of the components of Melaleuca alternifolia (tea tree) oil

AIMS

To investigate the in vitro antifungal activity of the components of Melaleuca alternifolia (tea tree) oil.

METHODS AND RESULTS

Activity was investigated by broth microdilution and macrodilution, and time kill methods. Components showing the most activity, with minimum inhibitory concentrations and minimum fungicidal concentrations of < or =0.25%, were terpinen-4-ol, alpha-terpineol, linalool, alpha-pinene and beta-pinene, followed by 1,8-cineole. The remaining components showed slightly less activity and had values ranging from 0.5 to 2%, with the exception of beta-myrcene which showed no detectable activity. Susceptibility data generated for several of the least water-soluble components were two or more dilutions lower by macrodilution, compared with microdilution.

CONCLUSIONS

All tea tree oil components, except beta-myrcene, had antifungal activity. The lack of activity reported for some components by microdilution may be due to these components becoming absorbed into the polystyrene of the microtitre tray. This indicates that plastics are unsuitable as assay vessels for tests with these or similar components.

SIGNIFICANCE AND IMPACT OF THE STUDY

This study has identified that most components of tea tree oil have activity against a range of fungi. However, the measurement of antifungal activity may be significantly influenced by the test method.

Antifungal activity of volatile compounds generated by essential oils against fungi commonly causing deterioration of bakery products

AIMS

To investigate the volatile fractions of 16 essential oils for activity against the more common fungi causing spoilage of bakery products, Eurotium amstelodami, E. herbariorum, E. repens, E. rubrum, Aspergillus flavus, A. niger and Penicillium corylophilum.

METHODS AND RESULTS

The study applied 50 microl of pure essential oils in a sterilized filter paper, were carried out at pH 6 and at different water activity levels (0.80-0.90). First, a wheat flour based agar medium was used, where cinnamon leaf, clove, bay, lemongrass and thyme essential oils where found to totally inhibit all microorganisms tested. These five essential oils were then tested in sponge cake analogues, but the antifungal activity detected was much more limited.

CONCLUSION

Five essential oils showed potential antifungal capacity against all species tested, over a wide range of water availability. Their activity, however, seems to be substrate-dependent. More research is needed to make them work in real bakery products, as in the preliminary study limited effectiveness was found.

SIGNIFICANCE AND IMPACT OF THE STUDY

The potential of the cinnamon leaf, clove, bay, lemongrass and thyme essential oils against species belonging to Eurotium, Aspergillus and Penicillium genus has been demonstrated.

In-vitro and in-vivo anti-Trichophyton activity of essential oils by vapour contact

The minimum inhibitory doses (MIDs) of essential oils by vapour contact to inhibit the growth of Trichophyton mentagrophytes and Trichophyton rubrum on agar medium were determined using airtight boxes. Among seven essential oils examined, cinnamon bark oil showed the least MID, followed by lemongrass, thyme and perilla oils. Lavender and tea tree oils showed moderate MID, and citron oil showed the highest MID, being 320 times higher than that of cinnamon bark oil. The MID values were less than the minimum inhibitory concentration (MIC) values determined by agar dilution assay. Furthermore, the minimum agar concentration (MAC) of essential oils absorbed from vapour was determined at the time of MID determination as the second antifungal measure. The MAC value by vapour contact was 1.4 to 4.7 times less than the MAC remaining in the agar at the time of MIC determination by agar dilution assay. Using selected essential oils, the anti-Trichophyton activity by vapour contact was examined in more detail. Lemongrass, thyme and perilla oils killed the conidia, inhibited germination and hyphal elongation at 1-4 micrograms ml-1 air, whereas lavender oil was effective at 40-160 micrograms ml-1 air. The in-vivo efficacy of thyme and perilla oils by vapour contact was shown against an experimental tinea pedis in guinea pigs infected with T. mentagrophytes. These results indicated potent anti-Trichophyton action of essential oils by vapour contact.

A survey of the enterococci isolated from an artisanal Italian goat's cheese (semicotto caprino)

Enterococci were isolated from semicotto caprino cheese, a traditional cheese produced in Southern Italy: they were a significant part of the microbial population of this cheese, confirming the importance of the presence of these micro-organisms during cheese-making and ripening. They were also identified and studied for their phenotypic and genotypic characteristics: Enterococcus faecalis and Ent. faecium were the most frequently isolated species, followed by Ent. durans, Ent. hirae and Ent. gallinarum. None of the isolates showed lipolytic activity, whereas they were characterized by a relevant proteolytic activity as well as an antagonistic activity towards Listeria innocua. One strain of Ent. gallinarum showed a low-level resistance to vancomycin, while six out of the 79 Ent. faecalis strains possessed beta-haemolysis reaction. The highest acidifying potential in skim milk was obtained by Ent. faecalis isolates. Thirty enterococcal strains representative of the different species at different ripening times were analysed by means of RAPD-PCR, and revealed species-specific profiles for all the considered species.

Antimicrobial agents from plants: antibacterial activity of plant volatile oils

The volatile oils of black pepper [Piper nigrum L. (Piperaceae)], clove [Syzygium aromaticum (L.) Merr. & Perry (Myrtaceae)], geranium [Pelargonium graveolens L'Herit (Geraniaceae)], nutmeg [Myristica fragrans Houtt. (Myristicaceae), oregano [Origanum vulgare ssp. hirtum (Link) Letsw. (Lamiaceae)] and thyme [Thymus vulgaris L. (Lamiaceae)] were assessed for antibacterial activity against 25 different genera of bacteria. These included animal and plant pathogens, food poisoning and spoilage bacteria. The volatile oils exhibited considerable inhibitory effects against all the organisms under test while their major components demonstrated various degrees of growth inhibition.

Enterococci at the crossroads of food safety?

Enterococci are gram-positive bacteria and fit within the general definition of lactic acid bacteria. Modern classification techniques resulted in the transfer of some members of the genus Streptococcus, notably some of the Lancefield's group D streptococci, to the new genus Enterococcus. Enterococci can be used as indicators of faecal contamination. They have been implicated in outbreaks of foodborne illness, and they have been ascribed a beneficial or detrimental role in foods. In processed meats, enterococci may survive heat processing and cause spoilage, though in certain cheeses the growth of enterococci contributes to ripening and development of product flavour. Some enterococci of food origin produce bacteriocins that exert anti-Listeria activity. Enterococci are used as probiotics to improve the microbial balance of the intestine, or as a treatment for gastroenteritis in humans and animals. On the other hand, enterococci have become recognised as serious nosocomial pathogens causing bacteraemia, endocarditis, urinary tract and other infections. This is in part explained by the resistance of some of these bacteria to most antibiotics that are currently in use. Resistance is acquired by gene transfer systems, such as conjugative or nonconjugative plasmids or transposons. Virulence of enterococci is not well understood but adhesins, haemolysin, hyaluronidase, aggregation substance and gelatinase are putative virulence factors. It appears that foods could be a source of vancomycin-resistant enterococci. This review addresses the issue of the health risk of foods containing enterococci.

Enterococci in milk and milk products

Enterococci are widely distributed in nature. They gain entry into milk and milk products through the water supply, equipment, and insanitary and unhygienic conditions of production and handling. They have been incriminated as direct or indirect agents of disease. The evidence concerning their involvement is only circumstantial. These reports are also disputed as the disease symptoms have not been experimentally induced in animal models. However, there is sufficient evidence to indicate that prolific growth of enterococci in foods may lead to formation of clinically significant levels of pressor amines. These amines are very thermostable and therefore remain active even after heat processing, which eliminates all viable streptococci. These pressor amines may be involved in the onset of migraine attacks and produce hypersensitive crises in psychiatric patients who are being treated with monoamine oxidase inhibitors for depression.