Effect of antibiotics on the resistance of white mice to C1. perfringens toxin]

The effect of potassium benzylpenicillin, streptomycin sulfate and chlortetracycline on experimental gangrenous intoxication was studied. When the antibiotics were injected before intoxication, the albino mice resistance did not significantly change. When the antibiotics were injected immediately after the toxin administration, the resistance of the test animals markedly decreased.     

Effect of some antibiotics on the resistance of white mice to staphylococcal toxin]

Penicillin and streptomycin in experimental staphylococcal intoxication had different effects on the disease depending on the period of their use. Penicillin injections prior to administration of the toxin increased significantly the resistance of the animals to it, while with the use of streptomycin there was only a tendency to its increase. The use of both antibiotics against the background of the intoxication had a reverse effect: there was a tendency to a decreased animal resistance to a greater extent with the use of streptomycin. The use of tetracycline hydrochloride had no effect on the animal resistance to the staphylococcal toxin.     

Identification of residues critical for toxicity in Clostridium perfringens phospholipase C, the key toxin in gas gangrene.

Clostridium perfringens phospholipase C (PLC), also called alpha-toxin, is the major virulence factor in the pathogenesis of gas gangrene. The toxic activities of genetically engineered alpha-toxin variants harboring single amino-acid substitutions in three loops of its C-terminal domain were studied. The substitutions were made in aspartic acid residues which bind calcium, and tyrosine residues of the putative membrane-interacting region. The variants D269N and D336N had less than 20% of the hemolytic activity and displayed a cytotoxic potency 103-fold lower than that of the wild-type toxin. The variants in which Tyr275, Tyr307, and Tyr331 were substituted by Asn, Phe, or Leu had 11-73% of the hemolytic activity and exhibited a cytotoxic potency 102- to 105-fold lower than that of the wild-type toxin. The results demonstrated that the sphingomyelinase activity and the C-terminal domain are required for myotoxicity in vivo and that the variants D269N, D336N, Y275N, Y307F, and Y331L had less than 12% of the myotoxic activity displayed by the wild-type toxin. This work therefore identifies residues critical for the toxic activities of C. perfringens PLC and provides new insights toward understanding the mechanism of action of this toxin at a molecular level.     

Histochemical and electron microscopical studies of skeletal muscle affected by gas gangrene.

Ultrastructural and histochemical changes of skeletal muscle were studied in three patients affected with gas gangrene. There was complete lack of the phosphorylase, succinate dehydrogenase and adenosine triphosphatase activities in the affected muscles of all the patients. In unaffected muscles these enzymes showed weaker activities than in norm. The lactate dehydrogenase activity, especially the heart type isozyme (LDH-1 or H4) proved less sensitive to the effect of clostridial toxin. A general increase in the acid phosphatase activity was found both in affected and in unaffected muscles. On electron microscopic examination damage to sarcolemmal membrane and disintegration of myofilaments was seen. The mitochondria were swollen and their cristae distorted and fragmented.     

Effect of carbohydrates and control of culture pH on beta toxin production by Clostridium perfringens type C.

Clostridium perfringens type C strain CN 5384 produced a higher level of beta toxin in a controlled pH medium containing 1% glucose, starch, or sucrose than in media with dextrin, fructose, or raffinose. Toxin synthesis was not related to the growth yield. The effect of glucose on beta toxin production by 11 strains was investigated with and without control of the culture pH at 7.5. Strain CN 5386 produced distinctly higher toxin when the pH of the culture was maintained at 7.5, compared with uncontrolled pH.     

The time-dose relationship in experimental poisoning of white mice with botulinum toxin type A and by the intraperitoneal route

лзучалсь зависимость времени выживания белых мышей весом в 18г после внутрибрюшиного введения различных доз токсиндиализатов Clostridium botulinum типов А и В в разведении 0,85% раствором NaCl. Токсин типа А исследовался в пределах 1-16000 DLM, токсип типа В-в пределах 1-64000 DLM. Экспериментально полученпые величинны приблизтельно сходны с експоненциальными кривыми, ?ормулы которых для каждого типа токсина были выведены эмпирическим путем. Эта зависимоств соответствовала токсинлидиализатам обоих типов, если они были разведны по крайнней мере в 10 раз ?изиологичесим раствором. Прм разведении тедении токсина в каком-нибудь из т.н. потенцирующих ?акторов (напр., молоко, пептон ит. п.) ход кривых несколько менялся. Точноств метода дана процентной средной квадратической ошибкой определений на 1 животном, которая для всей исследуемой группы бывала приблизительно одинаковой и составляла для типа А около ±20%, а для типа В-около ±13%.     

Effect of immunomodulators on potato resistance and susceptibility to Phytophthora infestans

The mechanisms of induced resistance and susceptibility of potato (Solanum tuberosum L.) tubers to late blight agent (Phytophthora infestans Mont de Bary) were studied using an elicitor chitosan and an immunosuppressor laminarin. It was elucidated that treatment of disks from potato tubers with chitosan resulted in salicyclic acid (SA) accumulation due to activation of benzoate-2-hydroxylase and hydrolysis of SA conjugates. Such SA accumulation in potato tissues inhibited one of the antioxidant enzymes, catalase, inducing an oxidative burst and resistance development. The mechanisms of induced susceptibility to the late blight causal agent were studied using an unspecific immunosuppressor, laminarin, an analogue of natural specific suppressor of potato immune responses, β-1,3,β-1,6-glucan. It was established that the development of immunosuppression in tissues treated with laminarin did not affect the SA level in tissues. However, catalase sensitivity to SA reduced in laminarin-treated tissues, and the enzyme activity increased. In its turn, this might result in the reduced level of hydrogen peroxide in the cells and, as a sequence, in the increased potato susceptibility to late blight.     

The production and evaluation of monoclonal antibodies to Clostridium perfringens type D epsilon toxin

The production of five monoclonal antibodies to the epsilon prototoxin of Clostridium perfringens is described. All five monoclonal antibodies located three proteins in a trypsinized preparation of epsilon prototoxin. These proteins were located at 37.6 kDal, 35.6 kDal and 33.7 kDal by Western blots. Two of the monoclonal antibodies, M26/2 and M27/12, neutralized epsilon toxin in the mouse lethality assay. Four of the five monoclonal antibodies are considered suitable as reagents to detect epsilon toxin in assay procedures.     

Effect of Lactobacillus fermentum on beta2 toxin production by Clostridium perfringens

Clostridium perfringens, although a member of the normal gut flora, is also an important cause of intestinal disease in animals and, to a lesser extent, in humans. Disease is associated with the production of one or more toxins, and little is known about environmental influences on the production of these toxins. One of the health-promoting effects of lactic acid bacteria (LAB) is the establishment and maintenance of a low pH in the intestine since an acidic environment inhibits the growth of many potentially harmful bacteria. Here, the effect of the LAB Lactobacillus fermentum on beta2 toxin production by C. perfringens is described. Coculturing of C. perfringens with L. fermentum showed that under in vitro conditions, L. fermentum was capable of silencing beta2 toxin production by C. perfringens without influencing bacterial viability. The reduction in toxin production was shown to be most likely a result of the decline in pH. Quantitative PCR showed that the reduction in beta2 toxin production was due to a decrease in cpb2 mRNA. These results suggest that in the intestine, the production of beta2 toxin by C. perfringens might be regulated by other members of the normal intestinal flora.     

Effect of antibiotics on the resistance of white mice to infection caused by antibiotic-resistant Staphylococcus strains]

The effect of benzylpenicillin, streptomycin and tetracycline on the animal resistance to infection caused by the antibiotic resistant staphylococci was studied. It was found that the effect of the antibiotics on the infectious process outcome was not limited by their antibacterial properties. Changes in the natural resistance of the host under the effect of the antibiotics were not always the same and depended on both the antibiotic type and the moment of its administration.