Decreased oral colonization of Streptococcus mutans during aging of Sprague-Dawley rats

The colonization by streptomycin-resistant Streptococcus mutans strains of the teeth of conventional and ex-germfree Sprague-Dawley rats of various ages fed either a high-sucrose or a high-glucose diet was studied. Bacterial colonization occurred with increasingly greater difficulty as the rats became older. This was observed in studies of the implantation of the test organism after oral inoculation with different cell numbers as well as its transmission between infected and uninfected rats. With rat fed sucrose diet, the effect of age could not be demonstrated until they were age 3 months or older; the results from rats fed a glucose diet suggest that changes may already have occurred early after weaning. Changes in susceptibility to colonization during aging manifested themselves as a decrease in the proportions of rats which became infected as well as lower population levels in infected rats. The possible mechanism(s) involved as well as the possible significance of the findings was discussed.     

Cyotchemical indices of the protein-synthesizing apparatus of hyperchromic nerve cells

Cytophotometric, interferometric and autoradiographic methods were applied to evaluate hyperchromic motoneurons (HM) from spinal cord of mice which were allowed to swim for 4 hours. The HM in comparison with the normochromic motor nerve cells are characterized by a higher RNA content and a lower dry weight of perikaria. The autoradiographic data with H3-uridane make it possible to suggest that RNA exchange between the nucleus and cytoplasm of HM is accelerated. The mode of distribution of labelled proteins along the sciatic nerve 6 days after the local injection of H3-leucine in the ventral horn of L3--L4 spinal cord segments allows to conclude that the amount of protein transported with the slow component of axonal flow in the cases connected with the increase of the number of HM in corresponding nuclei is changed.     

A genetic and physiologic study of mutations of T4 phage suppressing the lysis defect of gene stII mutants

A new gene rVI phage T4B is found. Mutations rVI belong to the class of r-mutations of T4B. Mutations rVI do not show the lysis inhibition after superinfection and determine the r-morphology of plaques on Escherichia coli CR63 lawn. Mutations rVI are gene-specific suppressors of stII lysis defect, but do not suppress the e lysis defect. Alleles rVI and rVI+ are co-dominated with regard to the ability to suppress the stII lysis defect. The suggest the stoichiometric character of rVI gene function. Mutations rVI increase the permeability of infected cells before the lysis. The gene rVI located between the genes 56 and 39 on the T4B genetic map, close to the gene 56. The still mutations described earlier (Krylov, Yankovsky, 1973) suppress the lysis defect of the am z25 mutant in the gene e. The suppression is manifested when infected bacteria develope only in the liquid media.