摘要:

AbstractThe ability of serum complement to kill bacteria has been linked to host resistance to Gram-negative bacteria. A mechanism for killing extracellular organisms during early invasion, following release from infected phagocytic cells, or during bacteremia would contribute to a host's ability to resist disease. In fact, the ability of serum complement to kill bacteria has been linked to disease resistance.Brucella abortusare Gram-negative intracellular pathogens. Resistance to these bacteria involves the coordinated activities of the cellular and humoral immune systems. The existence of serum-resistant forms ofB. abortushas been established, and it has been shown that these bacteria can resist the killing action of complement even in the presence of specific antibody. Antibody is usually necessary for complement-mediated killing of smooth (virulent) forms of Gram-negative bacteria. An anomolous situation exists with some isolates of smoothB. abortus. Sera containing high titers of specific antibody do not support killing unless they are diluted. In the bovine, this phenomenon is associated with IgGl and IgG2 antibodies. This finding may account for the lack of positive correlation between antibody levels and resistance to disease, which has led, perhaps wrongly, to the idea that antibody and complement are not important in resistance to brucellosis.Available evidence suggests that antibody may have contradictory roles in the interactions between a host and bacteria. Avirulent (rough) forms of the organism would be rapidly killed by complement shortly after invasion, but serum-resistant smooth forms would survive and invade resident phagocytic cells. During the process of invasion and phagocytosis, the bacteria would initiate an immune response. With time, someB. abortusorganisms would be released from infected phagocytic cells. In the early stages of this process, the bacteria would encounter IgM antibody and low concentrations of IgG antibody. These would cause complement-mediated killing, and infection would be restricted to resident phagocytic cells. However, the immune response toB. abortusantigens would be intensified, and IgG antibody levels would increase. High concentrations of antibody do not support complement-mediated killing of extracellularB. abortus, but the bacteria would be opsonized by antibody and complement component fragments. This would lead to increased phagocytosis of extracellularB. abortusas they appear, and concomitant extension of disease. Because die high levels of antibody would block complement-mediated lulling ofB. abortus, resistance to disease at this point would be dependent on cell-mediated immunity.

ISSN:1040-841X    

DOI:10.3109/10408419509113538

出版商:Taylor&Francis    

年代:1995

数据来源: Taylor

摘要:

AbstractBacteria exhibit unique diversity in their ability to grow at different temperatures. Indeed, eubacteria and archaebacteria are the only organisms able to grow above 65d`. The temperature range for a species is generally considered to be a stable character; however, mutants may be isolated mat have a Tminor Tminbelow or above the parent organism. Some bacteria may also be coaxed to grow at different temperatures by training cultures, through an incremental increase or decrease of temperature. Genetic approaches, for example, the transformation of mesophilicBacillusto thermophily using DNA from closely related thermophiles, has been very controversial. A major problem has been the lack of stability of the high-temperature phenotype upon subculture, which has not allowed extensive genetic and biochemical characterization of the transformants. The mechanism whereby the thermophilic phenotype is carried is unknown, although it is possible that the adapter genes are plasmid encoded. Studies using phenotypically stable transformants indicated that the thermostability of some cellular components was significantly increased, both in the vegetative cell and spore state. Enzyme thermostability, for example, appeared to be associated with an increased use of hydrophobic amino acids; however, the biochemical mechanisms for these alterations remain unknown. Thermophily is still a challenging problem with some interesting molecular biology.

ISSN:1040-841X    

DOI:10.3109/10408419509113539

出版商:Taylor&Francis    

年代:1995

数据来源: Taylor

摘要:

AbstractLactobacillus acidophilusis considered to possess health-promoting attributes. These include anticarcinogenic and hypocholesterolemic properties and antagonistic action against intestinal and food-bome pathogens.L acidophiluscan also survive the hostile environment and establish in the complex ecosystem of the gastrointestinal tract. Therefore, the beneficial effects of ingestingL. acidophilusaccrue over a longer period than those organisms that cannot colonize the gut. However, the exact mechanisms of these attributes are not known. Presumably, the anticarcinogenic activity may be attributed to production of compounds and/or conditions that inhibit the proliferation of tumor cells, suppression of microorganisms that convert procarcinogens to carcinogens, and degradation of carcinogens formed. The hypocholesterolemic effect is probably exerted by inhibition of 3-hydroxy-3-methylglutaryl CoA reductase, which is a rate-limiting enzyme in endogenous cholesterol biosynthesis in the body and by promoting the excretion of dietary cholesterol in feces as a result of coprecipitation in the presence of deconjugated bile acids in the intestine and/or adsorption by the organisms. The antagonistic effect against pathogens and other organisms is possibly mediated by competition for nutrients and adhesion sites, formation of metabolites such as Organic acids, hydrogen peroxide, and production of antibiotic-like compounds and bacteriocins.

ISSN:1040-841X    

DOI:10.3109/10408419509113540

出版商:Taylor&Francis    

年代:1995

数据来源: Taylor