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101.
The AIDS epidemic has transformed the importance of cytomegalovirus (CMV) as a pathogen for the adult human central nervous system (CNS). At autopsy, about 25 percent of AIDS cases have cytopathologic evidence of CNS infection by CMV. Since almost nothing is known of the host CNS-viral interactions, we have developed a laboratory model of CMV infection of the brain in the guinea pig. In the present paper, we review the syndromes of CMV infection of the human CNS and compare the neuropathological findings of the opportunistic CMV brain infection in AIDS with the model. Destructive meningoencephalitis, perivascular infiltrates, and subependymal inflammation are found in both, but the glial nodule is the most characteristic feature of each. Thus, we demonstrate that the model faithfully reflects the histopathology of the human disease. Furthermore, since we have found that CNS infection is achieved following systemic infection in the guinea pig, the model recapitulates the sequence of infection in humans.  相似文献   
102.
103.
The production of staphylococcal enterotoxins A (SEA) and B (SEB) was studied by inoculating six well-defined staphylococcal collection strains into cow's, goat's, or sheep's milk (individually or as a 50% mixture of cow's + goat's or cow's + sheep's), into brain heart infusion, and into a medium generally used to enhance the synthesis of enterotoxins (3+3 medium). Four of the strains used are considered to be SEB producers, another is considered an SEA producer, and the remaining strain is nonenterotoxigenic but produces large quantities of staphylococcal protein A. Staphylococcal protein A masked the results in most cases. Only one strain secreted exclusively SEB, while the other three SEB producers synthesized SEA in different amounts. We conclude that enterotoxin production depends on the natural substrate and may differ from the results obtained when the strain is grown on cellophane over agar to determine its toxigenicity.  相似文献   
104.
105.
Summary In enzymatic synthesis of cephalexin (CEX) from 7-amino-3-deacetoxycephalosporanic acid (7-ADCA) and D--phenylglycine methyl ester (PGM) using an acylase fromXanthomonas citri, it was found that the synthetic activity and conversion yield were enhanced markedly by depressing the water activity (a w ) of reaction system. This enhancement was probably resulted from the change of thermodynamic equilibrium and maximized at a range ofa w from 0.96 to 0.97.  相似文献   
106.
A stable shuttle vector which replicates in Escherichia coli and Clostridium perfringens was constructed by ligating a 3.6-kilobase (kb) fragment of plasmid pBR322 with C. perfringens plasmid pHB101 (3.1 kb). The marker for this shuttle plasmid originated from the 1.3-kb chloramphenicol resistance gene of plasmid pHR106. The resulting shuttle vector, designated pAK201, is 8 kb in size and codes for resistance to 20 micrograms of chloramphenicol per ml in both E. coli and C. perfringens. Following shuttle vector construction in E. coli, plasmid pAK201 was transformed into E. coli HB101 and C. perfringens ATCC 3624A, using intact cell electroporation. The transformation frequencies were 10(6) and 10(4) transformants per microgram of DNA in E. coli and C. perfringens, respectively. Restriction enzyme analysis of the chimera isolated from transformants of both microorganisms suggested that the plasmids were identical. Reciprocal transformation experiments in E. coli and C. perfringens indicated no difference in transformation frequency. Plasmid pAK201 was stable in C. perfringens following repeated transfer in the absence of chloramphenicol pressure. The restriction map of plasmid pAK201 shows six unique cut sites which should be useful for future genetic analysis and C. perfringens gene library construction.  相似文献   
107.
Mutant strains of Escherichia coli that lack one or all of the intact components of mannose permease do not support the growth of phage N4. Complementation experiments using three recombinant plasmids containing DNA fragments coding for the subunits of mannose permease revealed that among the three component subunits, II-PMan and II-MMan alone are sufficient to confer N4 sensitivity.  相似文献   
108.
Low density lipoprotein (LDL), a major cholesterol-carrying lipoprotein in the plasma, binds to its receptor through apoprotein B (Apo-B). The addition of LDL and Apo-B induced rapid (5 s), but transient increase in the inositol 1,4,5-trisphosphate (Ins-1,4,5-P3) level with K0.5 values of 1.1 and 0.07 microgram/ml, accompanied by increases of cytosolic free Ca2+ concentration [( Ca2+]i), in vascular smooth muscle cells (VSMC). The increases by LDL and Apo-B were both reduced by pretreatment of the VSMC with pertussis toxin. The early change in Ins-1,4,5-P3 involving a GTP-binding protein may function as an initial signal for the action of LDL in VSMC.  相似文献   
109.
DNA can be removed or separated by the selective adsorption/desorption on positively charged submicronsized polymeric particles (SSPP). The selective adsorption of DNA, in the presence of protein, on positively charged SSPP was accomplished by increasing the concentration of potassium phosphate or sodium phosphate. The adsorption of DNA was not affected by the concentration of potassium phosphate or sodium phosphate up to 1.2M. On the other hand, the adsoprtion of a protein (bovine serum albumin) was completely impeded by 170mM potassium phosphate. DNA adsorbed on SSPP could be desorbed by increasing the concentration of NaCl or KCl, thus it can be recovered. DNA desorbed from SSPP when the concentration of NaCl or KC was higher than 0.6M. A complete desorption of DNA was achieved at the concentration of NaCl or KCl above 1.2M.  相似文献   
110.
The design of a sliding controller for a continuous fermentation process is presented. The results obtained by simulation have proved the control scheme to be very robust. Regulation of substrate concentration at its optimal value has been achieved even though process parameters change their nominal values. Chattering effects are decreased by introducing a minor modification of the control variable around the sliding surface.  相似文献   
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