José L. Parada

Lactic acid bacteria growth promoters from Spirulina platensis

Spirulina has been used for many years as human food because of its high protein content and nutritional value. Some strains also produce bioactive substances that may inhibit or promote microbial growth. Lactococcus lactis, Streptococcus thermophilus, Lactobacillus casei, Lactobacillus acidophilus, and Lactobacillus bulgaricus were grown in rich media, MRS and RM, as well as in minimal saline medium with and without addition of extracellular products obtained from a late log phase culture of Spirulina platensis in Zarrouk medium. In both MRS and RM media, the extracellular products significantly promote the growth of the lactic acid bacteria assayed. This stimulatory effect was observed in media with pH adjusted to 5.3, 6.3 and 7.0. No effect was observed in minimal saline medium.

Effect of Spirulina platensis biomass on the growth of lactic acid bacteria in milk

The stimulatory effect of aqueous suspensions of Spirulina platensis dry biomass extracted at pH 6.8 and 5.5 was studied on four lactic acid bacteria (LAB) grown in milk. The addition of dry S. platensis to milk (6 mg/ml) stimulated growth of Lactococcus lactis by 27%. The growth of other strains was also promoted.

Microbiological and technological aspects of cassava-starch fermentation

The major genera found in the microflora of fermented, sour, cassava-starch were Streptococcus, Bacillus, Lactobacillus and Saccharomyces with amylase activity. Lactic acid bacteria predominated whereas the presence of moulds was not significant. No coliforms were detected. Electron microscopy showed bacteria and yeasts in contact with the starch granules and signs of erosion on the granule surface. Lactic acid was the main metabolite; no oligosaccharides, maltose or glucose were detected, indicating their rapid utilization. The degree of acidification, which correlated with the decrease in viscosity and the final quality of the product, was influenced by the variable microbial ecology.

Comparison of lactococcal bacteriophage isolated in the United States and Argentina

Bacteriophage of Lactococcus lactis ssp. lactis and ssp. cremoris, isolated in the United States and Argentina, were compared with respect to host range, adsorption, latent period, burst size and immunological cross-reactivity. Only 1 out of 13 U.S. culture isolates was sensitive to Argentinian phage. Argentinian L. lactis ssp. lactis C2 mutants were resistant to 13 U.S. phage isolates (4 prolate and 9 isometric). While Argentinian phage Stl-3 multiplied on U.S. culture isolate 59-1, low adsorption (38%) and insignificant burst size and latent period data were evident. Antisera prepared against U.S. phage D59-1 (prolate) and F4-1 (isometric) neutralized the lytic activities of all Argentinian prolate phage although the F4-1 antiserum was less effective. The data suggest homology especially between U.S. phage D59-1 and the Argentinian phage.

Assessment of virulence determinants in Yersinia enterocolitica 1A, O:5 strains isolated from chicken carcasses

The virulence potential associated with 42–45 MDa plasmid pYV, of three Yersinia enterocolitica, 1A, O:5, strains isolated previously from chicken carcasses was tested by plasmid extraction, and by four in vitro tests: (1) Auto-agglutination; (2) Calcium dependence for growth at 37 °C; (3) Congo Red and Crystal Violet binding; and (4) Resistance to the bactericidal effect of serum. The in vitro tests were negative in all strains tested, but from strain PP131 it was possible to extract a plasmid which was quite similar in size to the wild type pYV, but heavier and not observed in any other isolated strains. These contradictions between the presence of a plasmid of approximately 42–45 MDa and the in vitro tests negative results may suggest that there is no homology between the PP131 plasmid and pYV. From these results we conclude that the plasmid found in PP131 is not pYV and that the three Y. enterocolitica 1A, O:5, strains are non-pathogenic on pYV classical mechanism basis, which do not exclude the possibility of them becoming infectious by a different mechanism, especially in children or immune-depressed individuals.