Biomedical subjects
Publications and source records attributed to L E Ravdonikas.
The problem of conjugation in Streptococci is reviewed as a form of genetical information exchange in bacteria. The theoretical and experimental data of the recent years on the nature, mechanisms and role of conjugation in the spreading of drug resistance in the populations of pathogenic microorganisms are presented.
The paper presents data on the nature of the conjugation-like process (CLP) of genetic marker transfer on the membrane filters in group A streptococci. Studied are the CLP development depending on the duration of the donor-recipient contact and the influences of various physiological conditions on the degree of CLP manifestation and frequency. The effect of sub-inhibiting erythromycin concentrations on the frequency of the erythromycin marker transfer is first found. The original experimental evidence and literature data suggest a role played by transposing elements in CLP determination on the membrane filters in group A streptococci.
The international and original research data on the adhesion of group A and B streptococci are over-viewed. Based on the conducted studies, a conclusion has been drawn on the polyfactor pattern of pathogenic streptococci adhesions. The polyfactor pattern of adhesion is manifested in (a) different ranges of tissue sensitivity to streptococci adhesion, (b) a correlation between the adhesiveness and particular phenotypes (M(+)-M-; OF(+)-OF- in group A streptococci, TSA(+)-TSA- in group B streptococci), (c) different sensitivity of adhesives to proteolytic enzymes, and (d) interaction with fibronectin. M-protein was found to be involved in specific pyogenic streptococcal adhesion to the pharyngeal epithelium, which opens up new vistas for the search of approaches to the prevention of mucosal colonization. The participation of lipoteichoic acid (LTA) in group A and B streptococci adhesion in different tissues was shown The involvement of proteins in group B streptococcal adhesion was suggested by indirect evidence, which needs to be confirmed by direct isolation of an adhesive. It is suggested, that different quantitative combinations as well as structural organization of protein complexes and LTA in the streptococcus cell wall may determine the strain and species specificity of pathogenic group A and B streptococci interaction with host tissues.
Eighty-nine fosfomycin-resistant mutants of group A and B streptococci were isolated. The mutants differed essentially from the parent strains in cell-wall characteristics, such as morphology of cocci and chains, sensitivity to detergents and hydrophobic properties. At the same time, the recipient activity of the investigated mutants was not changed. It is supposed that resistance of mutants to fosfomycin is connected with a transport block of glycerol 3-phosphate--important lipoteichoic acid (LTA) structural component. Fosr mutants can be useful for experimental examination of Beachey's hypothesis about the importance of LTA or its complex with the M protein for adhesion.
Adherence of three strains of group A streptococci and their fosfomycin-resistant mutants to HEp-2 tissue culture cells was compared with some cell-surface characteristics, i.e. ultrastructure and hydrophobicity. Among Fosr mutants, both well-adhering and weakly adhering mutants were found. Clonal analysis of the mutants proved their greater stability in the adherence. Well-adhering parent strains of streptococci and Fosr mutants exhibited surface fibrillae in contrast to weakly adhering Fosr mutants which were devoid of fibrillae or contined fibrillae of lower electron density. Decrease of adherence of Fosr mutants of two strains was accompanied by a decrease of their hydrophobicity.
A simple method for the evaluation of the hydrophobic properties of streptococci, pathogenic for humans, by their adherence to polystyrene and a modified method for measuring their hydrophobic properties by their sorption on hexadecane have been developed. The results obtained in the evaluation of the hydrophobic properties of streptococci by these two methods have been compared and the complete correlation of these results in classifying the cultures as hydrophobic and hydrophilic has been shown. For the first time the differences in the hydrophobic properties of different strains of group B streptococci have been established.
Recently, we reported that conjugal transfer of plasmid pERL1, determining i.a. erythromycin resistance (Emr), into group A streptococci could trigger the expression of anti-phagocytic activity, adhesiveness, opacity factor and capacity to bind immunoglobulin Fc-parts and beta 2-microglobulin. In the present study, ethidium bromide treatment of Emr transconjugants allowed the selection of "cured", erythromycin sensitive (Ems) mutants. This procedure did not affect the expression of the abovementioned characteristics. However, when plasmid pERL1 was again transferred to two such mutants, the "secondary", Emr transconjugants obtained showed lack of each of these properties. Our experiments thus demonstrated a "switch-on" as well as a "switch-off" effect, exerted by the same plasmid, pERL1, on some major pathogenic properties of group A streptococci.
Transfer of five plasmids was studied in 30 different mating systems, involving streptococci of groups A, D and H. The erythromycin resistance marker (Emr) of all five plasmids was transferable at frequencies ranging from 8 X 10(-7) to 2 X 10(-4). All original donor strains except SM60 (pERL1) contained phage activity, but evidence was obtained favouring conjugation over transduction as the mechanism of transfer. The process was rec-independent. The transconjugants were able to serve as donors of the Emr-marker in secondary matings. A shortened derivate (pSM10) of the plasmid pSM10419 could also be transferred. Finally, the presence of the plasmid pSM15346 influenced the expression of the capacity to adhere to human epithelial cells and the resistance to UV-light of the host, whereas anti-phagocytic activity and production NADse and of opacity factor was unaffected by the plasmid.
The erythromycin-resistance marker of two plasmids, pSM19035 and pERL1, could be transferred by conjugation in matings within group A streptococci and between group H and group A streptococci, with a frequency of 10(-5) to 8 X 10(-7). Two of the recipient strains used, 22v-1 and 22v-2, showed traces of opacity factor (OF) activity. This activity increased markedly upon transfer of both plasmids to the strains, whereas a number of other recipients, viz. 22h-21, 12Teiko-1 and Challis 6-1, remained OF-negative after conjugation. Furthermore, the transconjugants resulting from matings using strains 22v-1 and 22v-2 as recipients expressed anti-phagocytic activity. Attempts were made to type the transconjugants but they did not belong to type M12, M22 (the types from which the parents were derived) M3 or M1. Concomitant with the expression of anti-phagocytic activity, IgG and IgA Fc-receptor activity occurred in the transconjugants of 22v-1 and 22v-2, whereas the donor and recipient cells were without receptors. It was not possible to demonstrate extrachromosomal DNA in transconjugants possessing anti-phagocytic, OF or Fc-receptor activity, although they retained their ability to serve as donors of the Emr marker. It is suggested that the triggering by plasmids of anti-phagocytic activity, OF and IgG and IgA Fc-receptors is due to insertion of plasmid DNA into the chromosome.
Sensitivity of the HEp-2 cell culture to the infection with the virulent salmonella strains was shown; active penetration and multiplication of bacteria in the monolayer cells indicated this. Gly 90, a glycerine mutant defective by glycerokinase, obtained under the action of ethylmethanesulphonate, displayed a distinct difference from the initial virulent strains of salmonella by decreased invasive properties and the absence of any capacity to multiplication in the epithelial cells. The data on the avirulence of the glycerine mutant obtained on a model in vitro confirmed the observations carried out in vivo in intraperitoneal infection of albino mice (LD50 = 1-10(7) cells) and in keratoconjunctival infection of guinea pigs.
The authors present the results of morphological study of experimentally-induced conjunctivitis and keratitis induced in guinea pigs by salmonellae. It was revealed that injuries of the conjunctiva and cornea in salmonellae infection were different by development and morphological manifestations from keratoconjunctivitis caused by shigellae. This difference was due to specific peculiarities of the pathogenic properties of salmonellae and shigellae clearly expressed on the given experimental model.
Complex microbiological and morphological study of the genetically connected Sh. flexneri strains, avirulent by keratoconjunctival test showed that the greatest extent of the virulent loss was revealed in shigellae with mutation in the area glpK-gene: they lost the capacity to penetrate into the cells of the bronchial epithelium, to resist local leukocytic reaction and to produce an injurious action on the pulmonary vessels. Shigellae with the replaced kcpA- gene area mostly lost the capacity to penetrate into the epithelial cells of mouse bronchi and were eliminated from the epithelium by the 9th hour after the administration. Xyl--avir-hybrids obtained from crossing of Sh flexneri with the streptomycin-resistant E. coli K12 donors were characterized by the loss of the capacity to prolonged reproduction in the organism of mice with the retention of the capacity to penetration into the epithelium, of the influence on the development of the leukocytic reaction and of the damaging effect on the pulmonary capillaries.
Explore the source record for details and available documents.
S. typhimurium glycerine mutants-gly 90 and gly 87 were obtained under the action of ethylmethanesulfonate. The mutants obtained were characterized by the site of block in the course of glycerine utilization:gly 90 mutant bore the mutation in the glp K-gene, this leading to the defect by glycerokinase-the enzyme of the first stage of glycerine metabolism; gly 87 mutant had derangements in the other stage of glycerine utilization. Both mutants lost their capacity to induce keratoconjunctivitis in guinea pigs, but differed by the LD50 value in intraperitoneal infection of albino mice (y gly 87--5 cells, y gly 90--1x10(7) cells).
Explore the source record for details and available documents.
Kasugamycin sensitivity in Escherichia coli depends on the specific enzyme methylating rRNA. Native group A streptococci (GAS) were found to be sensitive to kasugamycin. After introduction of the erythromycin gene located on the transposon Tn916E into GAS some of the strains obtained kasugamycin resistance together with erythromycin resistance (erm). One of these strains carrying the transposon in its chromosome was tested for methylase activity. It was demonstrated to be deficient in kasugamycin methylase (ksg). The presented data proves the presence of ksg methylase in GAS. Evolutionary relationship between erm and ksg genes is discussed.
Explore the source record for details and available documents.