Biomedical subjects
Publications and source records attributed to N Lers.
It is shown analytically that the W'/W index, the hyper-Wiener index, and the Wiener number are closely related graph-theoretical invariants for acyclic structures. A general analytical expression for the hyper-Wiener index of a tree is derived too.
Use of molecular genetic methods in the study of sources and ways of spreading the infection provides precise data on the mutual clonal origin of the strains, on the basis of the determination of plasmid DNK maps. Results of the investigation of Salmonellae Wien strain show the same type of resistance to antimicrobial drugs and the impact of resistotypization as an epidemiologic marker. The analysis of the plasmid profile in these strains has confirmed the presence of FIme virulence plasmid of 80 megadalton in size and resistance plasmid of 60 megadalton which was by conjugation transferred to the recipient strain (in vitro experiment). The presence of antigen factors of colonization in escherichial coli, a cause of diarrhea, was confirmed: CFA-I in the serogroup 078, and CFA-II in the serogroup 06.
The mechanism of DNA replication in ultraviolet (UV)-irradiated Escherichia coli is proposed. Immediately after UV exposure, the replisome aided by single-strand DNA-binding protein (SSB) can proceed past UV-induced pyrimidine dimers without insertion of nucleotides. Polymerisation eventually resumes somewhere downstream of the dimer sites. Due to the limited supply of SSB, only a few dimers can be bypassed in this way. Nevertheless, this early DNA synthesis is of great biological importance because it generates single-stranded DNA regions. Single-stranded DNA can bind and activate RecA protein, thus leading to induction of the SOS response. During the SOS response, the cellular level of RecA protein increases dramatically. Due to the simultaneous increase in the concentration of ATP, RecA protein achieves the high-affinity state for single-stranded DNA. Therefore it is able to displace DNA-bound SSB. The cycling of SSB on and off DNA enables the replisome to bypass a large number of dimers at late post-UV times. During this late replication, the stoichiometric amounts of RecA protein needed for recombination are involved in the process of postreplication repair.
In the complexity of host tumor relations, the regeneration of the tissue in which the tumor is growing, or in some other tissue in the organism, could influence the maturation of tumor cells, i.e. tumor reversion. Clinical observations and experiments on plants, lower animals, or animal embryos, performed by several authors, and our results on the influence of regenerating mouse liver on the abilities of tumor transplanted there or elsewhere in the organism led us to study the in vitro growth of different cells or bacteria exposed to the extracts of normal or regenerating liver and/or sera from these animals. Further, sterile used bacterial media were added to bacterial or cell cultures, respectively. Depending on the model, liver extracts-particularly extracts and sera from mice with regenerating liver-were shown to inhibit radioactive thymidine incorporation in the cells. In these experiments, the number of bacteria or cells per culture was lower than in otherwise treated corresponding cultures. Further, used sterile media of bacterial cultures stimulated the growth of bacteria but inhibited thymidine incorporation into fibrosarcoma cells in vitro. Whether this means that one or several common regulators exist in nature appears as an intriguing, but still completely open question. The idea of controlling tumor growth by using such regulatory growth factors seems very provocative.
The hydrophobicity of the cell surface of Yersinia enterocolitica was investigated by the salting-out test. It was shown that plasmid-containing strains grown at 37 degrees C aggregated at a final concentration of (NH4)2SO4 of between 0.3 to 0.5 M. In contrast, the plasmid-free derivatives did not show aggregation even at a concentration of 2.0 M(NH4)2SO4. Therefore, the salting-out test can be utilized as a simple and reliable method for distinguishing plasmid-containing, virulent strains of Yersinia enterocolitica from their plasmid-free derivatives. This was also confirmed by the use of 30 clinical isolates of virulent Y. enterocolitica.
Stool specimens from 631 children with acute diarrhoea and from 277 healthy controls were tested for the presence of non-enteropathogenic, non-enterotoxigenic Escherichia coli strains which mediated mannose-resistant haemagglutination of human erythrocytes (MRHA+). Fifty-nine (34.9%) of 169 isolated MRHA+ strains but none of 210 MRHA- strains exhibited diffuse adherence (DA+) to HEp-2 cells. DA+ strains were found in 37 (5.9%) children with diarrhoea and in 22 (7.9%) controls. MRHA+/DA+ strains in comparison to MRHA+/DA- strains significantly less frequently expressed P fimbriae (10.7 vs. 73.6%), haemolysin production (12.5 vs. 63.2%), and MRHA of other species erythrocytes (21.4 vs. 84%). These data demonstrate that E. coli which exhibit the diffuse pattern of adherence to HEp-2 cells also cause MRHA of human erythrocytes. Since these strains were found with similar frequencies in children with and without diarrhoea it seems that DA is not a marker of enteropathogenicity of E. coli.
Post-ultraviolet DNA synthesis kinetics were investigated in the Escherichia coli uvrA recA strain and its isogenic counterpart, overproducing single-strand DNA-binding protein (SSB). It was demonstrated that large quantities of SSB enhance the capacity of the unmodified replisome to use the UV-damaged template for DNA synthesis. DNA thus synthesized is of low molecular weight, as shown by sedimentation in alkaline sucrose gradients. It is therefore suggested that SSB actively participates in the replisome translocation past dimers and/or the initiation of new DNA chains downstream of these lesions.
We studied photoreactivation in cells carrying the multicopy ssb+ plasmid. These cells overproduce single-stranded DNA-binding protein (SSB). Overproduction of SSB enhances the capacity for photoreactivation in recA bacteria but not in the recA+ background. It is suggested that, in recA cells, SSB binds to the dimer region of DNA and that this binding stimulates the process of photoreactivation. In recA+ cells, the same stimulation might be achieved by RecA protein.
UV-induced mutagenesis was investigated in the uvrB strain and its isogenic counterpart overproducing the single-stranded DNA-binding protein (SSB). It was demonstrated that overproduction of SSB significantly increases the frequency of mutation. Our results indicate that such an increase might be due to certain abnormalities in induction of the SOS response (untimely and prolonged activation of the RecA protein).
In the early applications of the connectivity index the index was empirically modified for some properties of cyclic structures by subtracting 1/2 from the computed value based solely on valence of vertices in the molecular graph. In this article we looked into the origin of this heuristic adjustment of the connectivity indices for cyclic structures. We have examined the relative role of carbon atoms in cycle-containing structures by differentiating carbon atoms making up a ring and carbon atoms in exocyclic bonds. We found in the case of the boiling points of cycloalkanes and alkylcycloalkanes that contributions of "cyclic" and "acyclic" atoms to molecular additivities differ somewhat.
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