Antibiotic resistance of Pseudomonas aeruginosa strains isolated from patients with infected burns

Sensitivity to 15 drugs of 248 P. aeruginosa strains isolated from patients with infected burns was studied by the method of agar dilution. All of the strains were resistant to polymyxin M, ceporin, erythromycin and oleandomycin. Most of the strains were resistant to streptomycin, monomycin, ampicillin and rifadin. Moderate resistance of the strains to carbenicillin, morphocycline, vibramycin, kanamycin, tetraolean and tetracycline was observed: the maximum concentrations of these antibiotics (128 microgram/ml) inhibited the growth of 85, 69, 63, 51.8, 43.6 and 41.2 per cent of the strains respectively. Gentamicin proved to be most active against the strains of P. aeruginosa and inhibited 87 per cent of the strains when used in the therapeutic doses. The study provided recomendation of the drugs for parenteral and local use in treatment of burns infected with P. aeruginosa.     

Study of the adaptation resistance in bacteria to membrane active polypeptide antibiotics

Variants of Micrococcus lysodeikticus resistant to 100 micrograms/ml of gramicidin S with preserved resistance in subcultures on media without the antibiotic were isolated as a result of prolonged adaptation on a solid medium with increasing concentrations of gramicidin. The sensitive and resistant cells did not differ by their ability to bind gramicidin. Under the antibiotic effect permeability of the cytoplasmic membranes of the intact cells in the sensitive bacteria appeared to be impaired to a greater extent than that of the membranes of the cells in the resistant variant. Comparison of the lytic activity of gramicidin and its derivatives with respect to the protoplasts prepared with the cells of the initial and resistant variants of M. lysodeikticus revealed much higher resistance of the resistant variant protoplasts to the membrane-disorganizing effect of the preparations. Malate dehydrogenase and NADH-oxidase in the membrane preparations of the resistant variant cells differed from analogous enzymes from the membranes of the initial strain by the levels of their activity and sensitivity to gramicidin. It is likely that during adaptation of M. lysodeikticus to gramicidin significant changes in the cell cytoplasmic membranes occurred.     

Influence of the iron saturation of bacteria on the phagocytic capacity of neutrophils

The comparative study of the adsorptive capacity of human blood neutrophils with respect to "iron saturated" cells of bacteria belonging to different systematic groups was carried out. A decrease in the phagocytic number by 22-76% of the control level was shown. In experiments with iron-saturated Gram positive bacteria the phagocytic number was noted to be less than the physiological norm.     

Sex ratio among human embryos and newborns in a Russian population

Summary A comparative study was performed on the sex ratio among embryos and newborns in a Russian population (Moscow).The secondary sex ratio was studied in 81 914 babies born in different regions of Moscow during the period 1962–1971. It was 105.8 boys to 100 girls. Neither maternal age nor month of birth was observed to have any effect on the secondary sex ratio.The sex chromatin was studied in 3000 embryos obtained from induced abortions. The ratio of male to female embryos was 103.4:100. It dose not differ from either Mendelian segregation (1:1) or the secondary sex ratio in a population studied. It was calculated that more precise determination of the sex ratio in the embryonal period would require the study of not less than 17 500 embryos.The confidence limits are presented for the significance of possible differences in the sex ratio in samples ranging from 100 to 500000 in size.

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Zusammenfassung In einer russischen Bevölkerung (Moskau) wurde das Geschlechts-verhältnis unter Embryonen und Neugeborenen verglichen.Das sekundäre Geschlechtsverhältnis (bei Neugeborenen) wurde bei 81 914 in Moskau geborenen Babys für den Zeitraum 1962–1971 untersucht. Ergebnis: 105,8 : 100. Weder das Alter der Mutter noch die Jahreszeit beeinflußte diesen Wert.Bei 3000 Embryonen aus induzierten Aborten wurde das Sex-Chromatin bestimmt. Es ergab sich ein Verhältnis 103,4 : 100 . Es besteht weder ein Unterschied zu dem erwarteten 1:1-Verhältnis noch zu dem sekundären Geschlechtsverhältnis. Für eine genauere Bestimmung wäre eine Stichprobe an mindestens 17 500 Embryonen erforderlich.Es werden die Vertrauensgrenzen für eine mögliche Änderung des Geschlechtsverhältnisses bei Stichprobengrößen von 100 bis 500000 Beobachtungen angegeben.

     

Melanin decreases clastogenic effects of ionizing radiation in human and mouse somatic cells and modifies the radioadaptive response

Melanin’s influence on the chromosome aberration frequency induced by radiation in human lymphocytes and mouse bone marrow cells has been studied. We revealed earlier that melanin significantly decreases the frequencies of different radiation-induced mutations in animal germ cells. Melanin protection in somatic cells has been found to be less effective. The melanin effect in somatic cells depends on radiation dose: the lower the damage level, the better the melanin protection. In order to determine the influence of melanin at low radiation doses, the adaptive response was investigated in mouse bone marrow cells in vivo. The level of chromosome aberrations in these cells after fractionated irradiation of 0.2 Gy+1.5 Gy with a 4-h interval was about half that after a single dose of 1.7 Gy. If melanin was injected prior to irradiation, the aberration level decreased by a factor of about two in both cases. This observed result may be due to the potential radioprotective effect of melanin and to the absence of any adaptive response, whereas in the case of melanin application between the priming and challenge doses, the combined effect of the adaptive response as well as melanin protection resulted in a 4-fold decrease of chromosome aberrations. These results allow us to draw the following conclusions: adaptive response can be prevented by a radioprotector such as melanin, and melanin is capable of completely removing low-dose radiation effects. Received: 2 December 1998 / Accepted in revised form: 15 September 1999     

Antibiotic resistance of hemolytic bacteria, depending on iron content in bacterial cells

The study of sensitivity to antibiotic substances of different chemical structure and the mechanism of the antimicrobial action of hemolytic bacteria Bacillus sp., Corynebacterium sp. and Escherichia coli under the condition of high iron content in bacterial cells was carried out. An increase in antimicrobial resistance of iron-loaded Gram-positive bacteria, in contrast to Gram-negative ones, was shown.     

Effect of salts on the lytic activity of gramicidin S and its derivatives

Potassium and sodium chlorides, sulfates, acetates and phosphates activated the lytic action of gramicidin S and its derivatives on protoplasts of M. lysodeikticus. The derivatives used were positively charged and neutral by the free amino groups in the ornithine moieties. The salts had no effect on lysis of the bacillar protoplasts by gramicidin S and its positively charged derivatives. The lytic effect of the neutral derivative on the bacillar protoplasts markedly increased in the presence of the salts, activation of the lysis by the phosphates being more pronounced than that by the other salts. Increased membrane activity of gramicidin S in the presence of the salts was not connected with association of the substance molecules in solution. Probably it was due to increased destruction of the membranes at the account of activated detergent effect of the antibiotic and its derivatives.