[Stability of Lactococcus lactis phages treated with sodium hypochlorite and during storage]. / Estabilidad de fagos de Lactococcus lactis frente al hipoclorito de sodio y durante el almacenamiento.

Survival of lytic bacteriophages active against Lactococcus lactis ssp. lactis and ssp. cremoris was determined after treatment with sodium hypochlorite and during storage at 4 degrees C. Three phages were isolated from dairy plants in Argentina (ARG) and the other phages were isolated in the United States of America (US). All of them represent phages that infected cheese manufacture industries and belong to different morphological or serological groups. These phages showed higher survival in M17 broth, buffered with sodium glycerophosphate, than in trypteine soy broth (TSB). Phage populations did not decrease significantly during 14 weeks in M17 broth, whereas in TSB the titers of phage suspensions began to decline around 9 days. In addition, the effect of sodium hypochlorite was more marked in broth than in milk. A higher surviving fraction was obtained in milk, even when tenfold higher concentrations of chlorine were used. The effect of hypochlorite on phages of the same serological group was quite similar and independent of phage morphology. However, phage 137-1, which belongs to other serological group, showed lower resistance to sodium hypochlorite. Comparing the hypochlorite inactivation for ARG and US phages, it was observed that they have their own inactivation values, independently of their origin and morphological group. Long periods of time and high concentrations of chlorine were necessary to reduce the surviving fraction in milk. This indicates that hypochlorite concentrations and times of contact can be critical for the efficiency of the operative sanitization processes.

Estabilidad de fagos de Lactococcus lactis frente al hipoclorito de sodio y durante el almacenamiento. / [Stability of Lactococcus lactis phages treated with sodium hypochlorite and during storage]

Survival of lytic bacteriophages active against Lactococcus lactis ssp. lactis and ssp. cremoris was determined after treatment with sodium hypochlorite and during storage at 4 degrees C. Three phages were isolated from dairy plants in Argentina (ARG) and the other phages were isolated in the United States of America (US). All of them represent phages that infected cheese manufacture industries and belong to different morphological or serological groups. These phages showed higher survival in M17 broth, buffered with sodium glycerophosphate, than in trypteine soy broth (TSB). Phage populations did not decrease significantly during 14 weeks in M17 broth, whereas in TSB the titers of phage suspensions began to decline around 9 days. In addition, the effect of sodium hypochlorite was more marked in broth than in milk. A higher surviving fraction was obtained in milk, even when tenfold higher concentrations of chlorine were used. The effect of hypochlorite on phages of the same serological group was quite similar and independent of phage morphology. However, phage 137-1, which belongs to other serological group, showed lower resistance to sodium hypochlorite. Comparing the hypochlorite inactivation for ARG and US phages, it was observed that they have their own inactivation values, independently of their origin and morphological group. Long periods of time and high concentrations of chlorine were necessary to reduce the surviving fraction in milk. This indicates that hypochlorite concentrations and times of contact can be critical for the efficiency of the operative sanitization processes.

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.

[A mutant of Streptococcus lactis with resistance to bacteriophages isolated in Argentina and the United States of America]. / Mutante de Streptococcus lactis con resistencia a bacteriófagos aislados en Argentina y Estados Unidos de América.

Streptococcus lactis and Streptococcus cremoris have an important role in the fermentation of milk during the manufacturing of lactic products. Bacteriophages are spread in the plant environment and they may infect the starters causing technical and economic problems to the dairy industry. It is now known that the usual methods of control are not completely safe against the proliferation of phages. It is necessary therefore to include resistant strains to the phages which infect the plant. This study introduces a simple and direct method to obtain spontaneous mutants which have performed clear resistance to a certain phage. The prolate (ARG) phages used in this work St11, St13 and St15 were isolated in Argentina, on S. lactis C2 while the prolate and isometric (AM) phages phi C2, D59-1, I16-1, and G72-1, F4-1, I37-1 respectively, were isolated in Cornell University. on the corresponding S. lactis strains except the phage D59-1 isolated on an S. cremoris strain. The propagation of phages was performed using M and M17 broth. The phage sensitivity was tested through spot test and overlay plaque plating method expressing the titre of phage suspension. as PFU/ml. In order to obtain spontaneous resistant mutants of S. lactis C2 to phage St15, and active culture of S. lactis C2 (sensitive) was spread on agar M plates, inoculated with drops of a suspension of phage St15 (10(8)PFU/ml) and incubated at 30 degrees C for 48 h. Colonies of mutants grown in the lytic areas caused by the phage were isolated and selected.(ABSTRACT TRUNCATED AT 250 WORDS)

Mutante de Streptococcus lactis con resistencia a bacteriófagos aislados en Argentina y Estados Unidos de América. / [A mutant of Streptococcus lactis with resistance to bacteriophages isolated in Argentina and the United States of America]

Streptococcus lactis and Streptococcus cremoris have an important role in the fermentation of milk during the manufacturing of lactic products. Bacteriophages are spread in the plant environment and they may infect the starters causing technical and economic problems to the dairy industry. It is now known that the usual methods of control are not completely safe against the proliferation of phages. It is necessary therefore to include resistant strains to the phages which infect the plant. This study introduces a simple and direct method to obtain spontaneous mutants which have performed clear resistance to a certain phage. The prolate (ARG) phages used in this work St11, St13 and St15 were isolated in Argentina, on S. lactis C2 while the prolate and isometric (AM) phages phi C2, D59-1, I16-1, and G72-1, F4-1, I37-1 respectively, were isolated in Cornell University. on the corresponding S. lactis strains except the phage D59-1 isolated on an S. cremoris strain. The propagation of phages was performed using M and M17 broth. The phage sensitivity was tested through spot test and overlay plaque plating method expressing the titre of phage suspension. as PFU/ml. In order to obtain spontaneous resistant mutants of S. lactis C2 to phage St15, and active culture of S. lactis C2 (sensitive) was spread on agar M plates, inoculated with drops of a suspension of phage St15 (10(8)PFU/ml) and incubated at 30 degrees C for 48 h. Colonies of mutants grown in the lytic areas caused by the phage were isolated and selected.(ABSTRACT TRUNCATED AT 250 WORDS)