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The gram-negative oral and systemic pathogen Aggregatibacter (Actinobacillus) actinomycetemcomitans produces a leukotoxin (LtxA) that is a member of the RTX (repeats in toxin) family of secreted bacterial toxins. We have recently shown that LtxA has the ability to lyse erythrocytes, which results in a beta-hemolytic phenotype on Columbia blood agar. To determine if LtxA is regulated by iron, we examined beta-hemolysis under iron-rich and iron-limiting conditions. Beta-hemolysis was suppressed in the presence of FeCl 3 . In contrast, strong beta-hemolysis occurred in the presence of the iron chelator deferoxamine. We found that secretion of LtxA was completely inhibited by free iron, but expression of ltxA was not regulated by iron. Free chromium, cobalt, and magnesium did not affect LtxA secretion. Other LtxA-associated genes were not regulated by iron. Thus, iron appears to play an important role in the regulation of LtxA secretion in A. actinomycetemcomitans in a manner independent of gene regulation.

Yersinia enterocolitica synthesized an exocellular antigen common to the serotypes associated with enterocolitis but absent from other serotypes or from other Yersinia species. Both virulent Ca2+-dependent and avirulent Ca2+-independent isogenic pairs derived from the enterocolitis-associated serotypes synthesized the common antigen. Requirements for the synthesis of this common antigen were (i) the presence of metabolizable sugars and (ii) growth on a solid medium at 37°C. The antigen was identified as a 24,000-dalton protein loosely associated with the cell surface but absent from either the cell envelope or the cytoplasmic fraction.

Esta investigación comprende la evaluación del concreto producido para cimentaciones de 10 edificaciones comunes en la ciudad de Jaén, donde se pudo observar que la elaboración del concreto se realiza de manera empírica sin un diseño de mezclas. La finalidad fue medir la resistencia a la compresión del concreto, estudiar los principales factores que intervienen sobre ésta, ensayos para lograr cada uno de los objetivos planteados y así establecer condiciones mínimas para una buena elaboración del concreto. Se evaluaron las dosificaciones utilizadas, proceso de preparación y colocación del concreto, características del concreto en estado fresco y endurecido de las cuales se han obtenido resultados alarmantes, la resistencia mínima promedio a los 28 días ha sido de 53.78 Kg/cm2 (Proyecto P-10) y la resistencia máxima promedio de 167.74 Kg/cm2 (Proyecto P-06), comprobándose las grandes deficiencias en la calidad del concreto. Después de evaluar los parámetros mencionados se determinó las principales características de los agregados, con las cuales se ha elaborado un diseño de mezclas, arrojando un resultado de resistencia promedio a los 28 días de 224.52 Kg/cm2. Finalmente se ha elaborado y difundido especificaciones técnicas mínimas que se deben cumplir para lograr una resistencia adecuada del concreto.

The presence of a 24,000-dalton surface protein in 215 isolates of Yersinia enterocolitica and related species was examined. By coagglutination with the specific antiserum, a 100% correlation with the pathogenic biogroups was found. Thus, this method is useful for the rapid screening of potential pathogenic Y. enterocolitica isolates.

All 20 0 serotypes of Serratia marcescens produce a common, soluble antigen. Crude antigen was obtained by ammonium sulfate precipitation of spent growth medium, antiserum was produced in rabbits, and a coagglutination test for rapid identification of S. marcescens was developed. A total of 701 clinical isolates of gram-negative bacilli were examined, and a 100% correlation between biochemical identification of S. marcescens and identification by coagglutination was found.