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A follow-up study of the 44 recipients of American Cancer Society, Inc., Special Postdoctoral Research Fellowship from 1962 to 1973 revealed that 11 of 21 M.D. candidates obtained their second (Ph.D.) degree at the end of training. By contrast, all but one among the 23 Ph.D. candidates were awarded the second (M.D.) degree. A great majority of either group remain in active research, regardless of whether or not they obtained the second degree. A very high percentage of their research is cancer related.

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Normal serum from the painted turtle (Chrysemys picta), the snapping turtle (Chelydra serpentina), and the frog (Rana pipiens) were found to possess bactericidal activity towards Leptospira. Leptospires from both the parasitic and biflexa complexes were killed by these sera at high dilutions. This pattern differs from that of mammalian serum, as generally only the biflexa complex leptospires are killed by normal mammalian serum. The activity in C. picta serum was characterized as being complement dependent and not mediated by basic proteins. Because comple-inactivated C. picta serum regained leptospiricidal activity after the addition of fresh rabbit serum, antibody is also likely to participate in the killing activity. Further support that C. picta serum contained leptospiral antibodies was found by the detection of serotype-specific agglutinins.

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This study was performed to determine the mechanism whereby hypertonic sucrose inhibits the immune bactericidal reaction. Other investigators had postulated that the initial attack of complement (C) on the cell wall was followed with lysozyme-containing whole serum by an enzymatic reaction upon the peptidoglycan substrate resulting in cell death. In the absence of serum lysozyme, secondary lethal changes might occur from damage to the cell's inner membrane as a result of osmotic forces in the presence of a defective cell wall. Hypertonic sucrose giving rise to plasmolysis and protection of the inner membrane was presumed to differentially inhibit the immune response mediated by lysozyme-free serum. The experimental results observed in this investigation have indicated, however, that the inhibitory effect of sucrose upon the bactericidal reaction may be explained simply by its anticomplementary effect and not by any effect on the bacterial cell. This view was supported by the following observations: (i) the comparability of the inhibitory effect of sucrose upon the immune hemolytic and bactericidal reactions, (ii) the comparable percentage loss in bactericidal activity of whole serum and lysozyme-free serum resulting from hypertonic sucrose, (iii) bactericidal antibody titrations were relatively unaffected and C titrations markedly inhibited by sucrose, (iv) the inhibitory effect of sucrose on the bactericidal reaction was unaffected by prior growth of the organism in the presence of sucrose, (v) the kinetics of the bactericidal reactivity of lysozyme-free serum in hypertonic sucrose, compared with whole serum, did not reveal a prolonged lag phase with lysozyme-free serum, but simply diminished reactivity at all times. These observations are compatible with the view that the C attack upon the outer surface of gram-negative bacteria, which plays a part in the cell's permeability control, may account for cell death. In this regard, the immune bactericidal reaction is quite comparable to the lysis of red cells or nucleated cells by C despite the lack of overt lysis in bacteria, probably because of their underlying supporting structures.

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The sensitivity of different bacteria to actinimycin D was not related to their cell surface morphology. Bacteria with simple and complex surfaces were both extremely susceptible.

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Strains of Pseudomonas aeruginosa isolated from clinical material were very variable in their sensitivity to the bactericidal action of normal serum mediated by the complement system. Fifty per cent killing end points ranged from 0.015 ml to greater than 0.4 ml. Most of the strains with relatively greater sensitivity to serum were isolated from patients with cystic fibrosis. Immunization of rabbits resulted in antisera with enhanced levels of bactericidal antibody, except with one strain which was resistant to the bactericidal action of normal serum and antiserum. When P. aeruginosa was cultivated at 41 C instead of at 37 C, it was significantly more sensitive to serum and to several antibiotics, thereby implicating fever as a host defense mechanism in Pseudomonas infections. In contrast to their heterogeneity to serum bactericidal activity, the strains were relatively homogeneous in their sensitivity to polymyxin, with no apparent association between their sensitivity to the two antimicrobial agents.

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When Escherichia coli K-12 was infected with lambda phage and mutants of lambda characterized by the production of temperature-sensitive repressors, the lysogenic bacteria were significantly more resistant to normal serum than the uninfected organisms. Infection of E. coli K-12 with a lambdoid phage, phi80, whose prophage attachment site is different from that of lambda, did not result in a detectable change in serum resistance. Similarly, infection with certain Pseudomonas and Shigella phages caused no detectable differences in serum resistance. Finally, the well-known conversion of the Salmonella anatum serotype to S. newington by E(15) phage indicated that, despite the relatively greater roughness of S. anatum, S. newington was more sensitive to normal serum than S. anatum. Thus, the effects of lysogeny on the sensitivity of bacteria to the bactericidal action of serum mediated by the complement system may be quite variable.

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Antimicrobial substances, including antibiotics such as polymyxin and novobiocin, detergents, and complement, all of which are known or presumed to have an effect upon membrane permeability, showed greater potency against ethylenediaminetetraacetic acid (EDTA)-treated Salmonella typhi than against untreated cells of that organism. The differential effect was particularly marked with the complement system when serum antibody was limiting. EDTA-treated cells were also more susceptible to penicillin and bacitracin. On the other hand, such treatment did not affect the potency against S. typhi of mitomycin C, the aminoglycosides, chloramphenicol, and chlortetracycline, nor did it affect the permeability of S. typhi to these compounds.

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Muschel, Louis H. (University of Minnesota, Minneapolis), and Karen Schmoker. Activity of mitomycin C, other antibiotics, and serum against lysogenic bacteria. J. Bacteriol. 92:967-971. 1966.-Lysogenic bacteria were found to be more sensitive to the bactericidal action of mitomycin C or streptonigrin than the corresponding sensitive or indicator strains. This result may be attributed to the induction of phage production in lysogenic cells by these antibiotics. Lysogenic and sensitive bacteria were, however, equally sensitive to chloramphenicol, streptomycin, and polymyxin B. In contrast to their greater sensitivity to certain phage-inducing antibiotics, the lysogenic state resulted in greater resistance to the bactericidal reaction of serum mediated by the complement system. In general, therefore, the lysogenic state may result in either decreased or increased sensitivity to various antimicrobial agents.

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