Behavior of enterotoxigenic strains of Staphylococcus aureus in milk fermented with a yogurt starter culture.

The ability of a yogurt starter culture formed by Streptococcus salivarius subsp. thermophilus and Lactobacillus delbrueckii subsp bulgaricus to inhibit the growth of four enterotoxin type A and B producers Staphylococcus aureus strains (ATCC 6538, S6, FRI-100 and a strain isolated from milk) during fermentation of milk and subsequent storage was investigated. Sterile skim milk was inoculated with about 10(6) CFU/ml of S. aureus and with about 10(6) CFU of starter culture, and incubated at 42 degrees C during 8 h, followed by refrigeration at 4 degrees C. Samples were taken every 2 h during fermentation and every 2 days during storage. Viable count of lactic acid bacteria and S. aureus as well as pH, acidity, thermostable deoxyribonuclease (TNase) and staphylococcal enterotoxin A (SEA) production were evaluated. Behavior of four strains was similar; S. aureus survived the 8 h fermentation with LAB, and its population began to decrease from the first day of storage, being completely inhibited at 9-10 days. TNase and SEA production were positive in all samples taken along the study. It was demonstrated that enterotoxigenic strains of S. aureus were able to survive the fermentation of milk with a yogurt starter culture and they were inhibited after several days during storage of the fermented product, contrary to the general belief which considered it very difficult due to the low pH. Even though S. aureus was inhibited, TNase and SEA were demonstrable along the storage. Therefore, fermented milks may play an important role in the transmission of this organism.

[Biological flow tracers: growth and survival of Bacillus subtilis 65-8 under environmental stress]. / Trazadores biológicos de flujos: crecimiento y sobrevivencia de Bacillus subtilis 65-8 bajo estrés ambiental.

Microbial flow tracers are presently limited to a strain of Bacillus globigii and a few highly specific bacteriophages. Bacillus subtilis 65-8 produces a black pigment as part of the primary metabolism under minimal nutritional conditions, with glucose as the sole carbon and energy source. This work shows that Bacillus subtilis 65-8 spores are thermostable (55 degrees C during 150 días), halotolerant (they germinate and grow in an enriched medium with up to 12% NaCl), persistent in a system of sand-soil and sewage, even in the presence of added commercial oil derivatives (kerosene, leaded gasoline and unleaded diesel), they are capable to move through porous systems even as the liquids, viscous as they may be, move through. Moreover, spores were resistant to the presence of autochtonous microorganisms in sewage, where we did not detect any other organism with differential characteristics like our strain (black pigment production in minimal medium) which could interfere with the identification of our biological flow tracer. The characteristics of Bacillus subtilis 65-8 make it a suitable biological flow tracer.

[Classification of Klebsiella strains with lectins]. / Clasificación de cepas de Klebsiella con lectinas.

Fourteen different plant seeds were used to obtain lectins which in turn were used to agglutinate 72 different serological strains of Klebsiella. The results were used to design a scheme which distinguishes 62 serotypes (91.6%) with a unique agglutination pattern with lectins. Two pairs of strains as well as two sets of three strains gave the same patterns. This procedure is useful as an alternative in the identification of strains for epidemiological purposes.

Paraoxon hydrolysis in human serum mediated by a genetically variable arylesterase and albumin.

Gel filtration chromatography resolves human serum paraoxonase into two fractions: (1) a high molecular weight fraction that is completely inhibited by EDTA and coelutes with arylesterase (E.C.3.1.1.2); and (2) a second fraction that is closely associated with albumin, is only partially inhibited by EDTA, and has relatively little arylesterase activity under the assay conditions used. The activity of the high molecular weight fraction is stimulated by NaCl, whereas the albumin associated activity is partially inhibited by NaCl and is not present in serum derived from an analbuminemic individual. Our data suggest that albumin itself, rather than a protein bound to or cofractionating with albumin, mediates paraoxonase activity. The variation in levels of the activity of the nonalbumin, high molecular weight enzyme is responsible for the observed polymorphism of paraoxonase activity in human serum or plasma. An optimal assay of polymorphic paraoxonase activity should be based on activity measurements of the nonalbumin fraction. It is considered likely that only the nonalbumin fraction is responsible for in vivo hydrolysis of paraoxon.

Phosphate dependence of monosaccharide transport in Nocardia.

Uptake of the monosaccharides d-glucose and d-mannose by Nocardia asteroides and N. brasiliensis is dependent on the presence of an adequate phosphate concentration in the environment. When phosphate is replaced by solutions of sodium chloride or potassium chloride of identical ionic strength, there is no sugar uptake. In the presence of iso-osmolar concentrations of sodium arsenate, there is, however, sugar uptake activation. When nonmetabolizable 3-O-methyl d-glucose is used, most of the sugar taken up can be shown to be in the cell at a concentration never exceeding that of the external medium. Phosphate, or arsenate, seems to be essential for the actual migration of the sugar through the cell envelope. The transport of the nonmetabolizable 3-O-methyl glucose also requires phosphate, and the transport seems to be of a type that does not require energy.