Heterotrophic soil bacteria, actinomycetes, and fungi produced nitrite when grown in media containing various reduced forms of nitrogen. Amines, amides, N-alkylhydroxylamines, oximes, hydroxamic acids, and aromatic nitro compounds served as substrates for nitrite formation by individual microorganisms. The yield of nitrite varied with the organism and the substrate, ranging from 190 ppm of nitrite-nitrogen with acetaldoxime as a nitrogen source to a few ppm with certain substituted ureas. None of the microorganisms formed nitrate from the substrates tested. One isolate, identified as a species of Fusarium, converted more than 90% of the nitrogen of pyruvic oxime to nitrite. Cell extracts of the fungus catalyzed the production of nitrite from the oxime.

Studies have been carried out on 86 samples of raw milk, 50 taken from the reception department of a dairy industry and the rest from three milking-sheds in the province of León. After a preliminary study of the properties of each sample (pH, total acidity, temperature, total number of microorganisms, staphylococci, probable positive coagulase staphylococci, and the verification, in 24 samples, of some staphylococci which survived a temperature of 71.5° C for a period of 16 seconds) the isolation of the distinguishable strains was carried out according to the different morphologies of the colonies. A total of 208 staphylococci were isolated, of which 58 proved to be coagulase positive. The isolated microorganisms have been amply characterized from the point of view of physiology, biochemistry and toxicity (verification of hemolysins and enterotoxin, but the latter in only 18 coagulase positive staphylococci). At the same time the coagulase positive microorganisms were submitted to phage typing (INTERNATIONAL SERIES and SETO-WILSON) and to antibiotic action in order to establish the proportion of staphylococci of milk origin resistant to these drugs. For the purpose of this study a new medium of selective culture (MAF) was used, based on the growth of staphylococci in anaerobic and semianaerobic conditions and the use of mannitol as a source of carbon in these circumstances. Due to the favourable results obtained with this medium, and also with the variation MAF-2, using egg-yolk, we propose its use as a new technique for the isolation of staphylococci of milk origin. From the results obtained in the preliminary study of the samples (all with minimum differences in acidity) it is deduced that the correlation intensity between some qualities of the samples is not as high as was to be expected if the principles on which these properties depend are taken into consideration (increase in acidity due to the fermentation of the lactose produced by lactic bacteria, and at the same time in relation with the temperature, number of microorganisms, etc.) underlining in this way the role of other milk qualities which are normally considered secondary (initial bacteriostatic power, buffer effect, fodder influence in its acidity, etc.). Enzymatic characterization has enabled a comparison of the tests used, underlining the fermentation of mannitol, phosphatase and desoxyribonuclease production as the most outstanding to determine the pathogenic capacity of staphylococci deduced in this case from its ability to coagulate rabbit and human plasma. Enterotoxin production was checked by inoculation in cats and was confirmed by gel-diffusion techniques in the 5 positive cases of the 18 tested. Experiments using the histamine valuation technique on an isolated organ (guinea pig ileum) and on cats' blood pressure, to diagnose enterotoxin, gave no practical result, but it was noticed, in all the microorganisms of complex enzymatic qualities tested, a light but persistent action, in the culture filtrates, on the guinea pig ileum submerged in a nutritious liquid. This action was of an antihistaminic nature. The phages which most frequently affected staphylococcus strains which were submitted to test were the 42E, 42D, 83A, 54 and 81 of the INTERNATIONAL SERIES and the S2, S5 of the SETO-WILSON SERIES. The signs of resistance to antibiotics in staphylococci of bovine origin are surprisingly high (22.2 % of the coagulase positive microorganisms) in a country in which the use of antibiotics in bovine medical treatment is not yet widely extended | Se han sometido a estudio 86 muestras de leche natural: 50 recogidas en la plataforma de recepción de una industria lechera y el resto en tres establos de la provincia de León. Después de un estudio previo de las propiedades de cada muestra (pH, acidez total, temperatura, número total de gérmenes, número de estafilococos, de estafilococos probables coagulasa positivos y determinación en 24 muestras de estafilococos supervivientes a la temperatura de 71,5 °C durante dieciséis segundos), se procedió al aislamiento de las cepas diferenciables por los caracteres de las colonias. Se aislaron un total de 208 estafilococos, de los cuales 58 resultaron ser coagulasa positivos. Los gérmenes aislados han sido ampliamente caracterizados desde los puntos de vista fisiológico, bioquímico y tóxico (determinación de hemolisinas y de enterotoxina, aunque esta última solamente en dieciocho estafilococos coagulasa positivos). Asimismo, los gérmenes coagulasa positivos fueron sometidos a la tipificación por fagos (series INTERNACIONAL y SETO-WILSON) y a la acción de antibióticos, con el fin de determinar la proporción de estafilococos resistentes a estas drogas en los de origen lácteo. Con ocasión del presente estudio, se probó un nuevo medio de cultivo selectivo (MAF), basado en el crecimiento de los estafilococos en condiciones de anaerobiosis o semianaerobiosis y en la utilización del manitol como fuente de carbono en estas circunstancias. En armonía con los favorables resultados obtenidos con este medio, así como con su variante MAF-2 (con yema de huevo), se propone su empleo como nueva técnica de aislamiento de estafilococos de origen lácteo. De los resultados obtenidos del estudio inicial de las muestras (todas ellas con variaciones mínimas de acidez), se deduce que la intensidad de correlación entre algunos caracteres de éstas no es tan elevada como era de esperar, si se consideran los principios de los que dependen estas propiedades (incremento de acidez debido a la fermentación de la lactosa producida por los gérmenes lácticos, y en relación a su vez con la temperatura, número de gérmenes, etc.), destacando así el papel de otras cualidades de la leche consideradas como secundarias (poder bacteriostático inicial, efecto tampón, influencia de la alimentación en la acidez, etc.). La caracterización enzimática ha dado lugar a una comparación de las pruebas utilizadas, destacando la fermentación del manitol, la producción de fosfatasa y de desoxirribonucleasa como las más sobresalientes a la hora de determinar la capacidad patógena de los estafilococos, deducida en este caso de su aptitud para coagular los plasmas de conejo y humano. La producción de enterotoxina se comprobó por inoculación al gato y se confirmó por técnicas de gel-difusión en los cinco casos positivos de los dieciocho probados. Los intentos realizados de utilizar la técnica de valoración de histamina sobre órgano aislado (íleon de cobayo) y presión sanguínea de gato, en el diagnóstico de la enterotoxina, no dieron resultado práctico; pero se observó, en todos los gérmenes ensayados de equipo enzimático complejo, una ligera pero persistente acción en los filtrados de cultivo sobre íleon de cobayo perfundido en un líquido nutritivo. Esta acción era de naturaleza antihistamínica. Los fagos que más frecuentemente lisaron las cepas de estafilococos sometidos a prueba fueron los 42E, 42D, 83A, 54 y 81 de la serie INTERNACIONAL, y los S2 y S5 de la serie SETO-WILSON. Los índices de resistencia a los antibióticos en estafilococos de origen bovino son sorprendentemente elevados (22,2 % de los gérmenes coagulasa positivos) en un país en que el empleo de antibióticos en la clínica bovina no está todavía masivamente difundido

The water-stability of sucrose-amended aggregates of Waupun silt loam incubated at 15, 25, and 35C, and the aggregate-stabilizing characteristics of microorganisms isolated from these aggregates were evaluated. Aggregate water-stability determined by wet-sieving was expressed as the percentage of soil material bound into water-stable aggregates 0.5 to 1 mm, 1 to 2 mm, and > 2 mm in size. Microbial development was investigated by microscopic and dilution plate techniques. Fungi isolated from the aggregates differed in their ability to effect aggregate stabilization in the presence and absence of sucrose. Stabil zation by effective fungi was a function mainly of the binding of soil particles into > 2-mm water-stable aggregates and was related closely to the onset and subsequent development of macroscopic mycelia on the aggregates. Stabilization of aggregates by sporeforming bacteria involved the production of a high percentage of <2-mm aggregates, especially in the early stages of incubation. Bacterial stabilization was initiated earlier but was maintained for a shorter time as incubation temperature increased from 15 to 35C; maximum aggregate stability effected at 15 and 25C was almost twice that reached at 35C. Maximum stabilization by the indigenous microflora occurred within 4 days at all 3 temperatures; appreciable stability was maintained for 84, 14, and 4 days at 15, 25, and 35C, respectively. Bacteria were primarily responsible for the initial stabilization of aggregates incubated at 15 and 25C and contributed to the initial stabilization of aggregates incubated at 35C. The fungal species involved in aggregate stabilization varied with temperature.