Factors affecting the lymphoid cells in the small intestinal epithelium of the mouse

The ontogeny of the lymphoid cells in conventional and germ-free mice has been studied. Development is similar in both groups up to the age of 4 weeks. During the first 2 weeks of neonatal life, few cells are present, but the numbers increase rapidly between 2 and 4 weeks of age. The number of cells continues to increase in conventional mice, but remains static in germ-free mice. Exposing adult germ-free mice to a conventional environment results in an increase in the size of the epithelial lymphocyte population to that characteristic of conventional mice. Rearing conventional weanling mice on antibiotic-treated drinking water does not prevent the post-weaning increase in lymphoid cell numbers. The results are interpreted as showing that the lymphoid cell population in the intestinal epithelium is part of the second-level or peripheral lymphoid tissue rather than part of the first-level systems such as the thymus and bursa of Fabricius.

Characterization of the aminopeptidase from Bacillus subtilis as an extracellular enzyme

A strain of Bacillus subtilis produced an aminopeptidase detectable in the cultural fluid and in cell-free extracts. Both extracellular and intracellular aminopeptidases hydrolyzed L-leucyl-β-naphthylamide substrate after activation with cobalt ions. In the cultural fluid, trace amounts of activity were present as early as 12 h, but the highest activity was attained between 36 and 96 h. The addition of lysozyme to cultures less than 36 h old inhibited the production of the aminopeptidase of the cultural fluid, but was less effective in older cultures. This trend was correlated to the Gram-variability of the organisms in the culture. Chloramphenicol and oxytetracycline also inhibited enzyme production without affecting normal cell lysis. These data were interpreted to imply that the aminopeptidase of the cultural fluid did not result from the release of the intracellular aminopeptidase by cell lysis, but that it was produced by viable, metabolizing cells, most probably Gram-negative. Chromatography of the cultural fluid on CM-Sephadex C-50 showed an aminopeptidase characteristic of the extracellular medium. The possible implication of this enzyme as a regulatory mechanism for nitrogen utilization by Bacillus subtilis is discussed.

The sensitivity of diphtheria bacilli to eight antibiotics

Antibiotics are of equal importance to antitoxin in the treatment of diphtheria, as an effective antibiotic rapidly halts the production of toxin. There appear to have been only two reports of the sensitivity of diphtheria bacilli to various antibiotics and these are based on the examination of less than 60 strains. In this paper the sensitivity of 192 strains to eight representative antibiotics is reported.