Hemolysin production, clumping (pheromone) response, transferability of the hemolytic trait, and drug resistance were examined in 97 clinical isolates of Enterococcus (Streptococcus) faecalis. The isolates were derived from various sources (i,e., urine, pus, vagina, sputum, bile, and blood), and approximately 60% were found to be hemolytic. About 85% of the hemolytic strains exhibited a clumping response, compared with about 49% of the nonhemolytic strains. Over 50% of the hemolytic strains carried transferable hemolysin determinants, and in no case were drug resistance genes linked. The hemolytic strains exhibited multiple drug resistance more frequently than did the nonhemolytic strains. In contrast to the high frequency of hemolysin producers among parenteral isolates, strains derived from fecal specimens of healthy individuals exhibited a low (17%) incidence of hemolysin production.
The conjugative plasmid pADl (56.7 kilobases) in Streptococcusfaecalis confers hemolysin-bacteriocin (Hly-Bcn) expression and a mating response to the sex pheromone cADl excreted by recipient cells. We examined the contribution of hemolysin to pathogenicity in intraperitoneally infected mice by using Tn916 and Tn917 insertion mutants altered in hemolysin expression. Strains exhibiting the normal hemolysin phenotype were significantly more virulent than the nonhemolytic insertion mutants. A mutant plasmid with an increased copy number which gave rise to a larger-than-normal zone of hemolysis on blood agar rendered host strains more virulent than the wild-type streptococci in mice.
ABSTRACT:A novel hybrid quantum mechanical (QM)/molecular mechanical (MM) approach that employs the real-space grids for the QM subsystem is proposed for investigating chemical reactions in an aqueous condensed phase. All of the Hamiltonian matrix elements including electric fields formed by the point charges on MM waters is represented in the real space. Details of the practical implementations are presented. The solute polarization, solvation structure, and the solvation energy of a water are computed, and the results are compared with those obtained by experiments and other QM/MM approaches that used the LCAO basis. It is shown that the real-space grid QM/MM method is adequate and superior for the description of the polarization of QM water in a water solution as well as in the gas phase. Solvation structures of classical water solvents are also properly reproduced by this method. Further, parallelization of the code is implemented on a distributed memory architecture, and it is demonstrated that the real-space grid approach is suitable for the high-performance parallel computing due to the localization of Hamiltonian operations in the real space.
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