Determination of the structural integrity of DNA from pathogenic enterobacteria

Among the enterobacterial strains under study, more organisms in the stationary phase of growth have been found to have nicks in their DNA than those in the exponential phase. Bacteria less sensitive to ultraviolet irradiation have the least number of nicks in each phase of growth. The number of nicks in different strains belonging to the serovar is sufficiently stable. Virulent and avirulent forms show no difference in this characteristic.     

Plant virus infection development as affected by heavy metal stress

The work was focused on the investigation of possible dependencies between the development of viral infection in plants and the presence of high heavy metal concentrations in soil. Field experiments have been conducted in order to study the development of systemic tobacco mosaic virus (TMV) infection in Lycopersicon esculentum L. cv. Miliana plants under effect of separate salts of heavy metals Cu, Zn and Pb deposited in soil. As it is shown, simultaneous effect of viral infection and heavy metals in tenfold maximum permissible concentration leads to decrease of total chlorophyll content in experiment plants mainly due to the degradation of chlorophyll a. The reduction of chlorophyll concentration under the combined influence of both stress factors was more serious comparing to the separate effect of every single factor. Plants' treatment with toxic concentrations of lead and zinc leaded to slight delay in the development of systemic TMV infection together with more than twofold increase of virus content in plants that may be an evidence of synergism between these heavy metal's and virus' effects. Contrary, copper although decreased total chlorophyll content but showed protective properties and significantly reduced amount of virus in plants.     

Characteristics of azithromycin action on bacterial biofilms of pneumonia pathogens]

Azithromycin (Zitrolid) action on biofilms formed by gramnegative and grampositive microorganisms, isolated from patients with respiratory tract infections was investigated. The drug was effective at the stage of the biofilm formation and on exposition to the already formed biofilms.     

Effect of SOS repair in enterobacteria on their interaction with the complement system

The interaction of E. coli (serovar 0124) and its rec A-mutants with serum complement resulting in the alternative pathway activation was studied. Bacteria VT1240 (original smooth strain), VT1241 (rough mutant) and VT 2240 (recA56 mutant) were shown to be complement-sensitive when treated with 1.5 X 10(8)--1.9 X 10(8) cells per ml of normal human serum, while the cells with SOS-activated system (recA441 mutant, strain VT3251) retained their viability. An alternative pathway of complement activation was minimal with E. coli VT1241, while VT3251 demonstrated intermediate activity. To decrease the level of complement components (AH50) and factor B (BH50) by 50%, 3.5 X 10(6)--4.5 X 10(6) cells of VT1240 and VT2240 strains were required. R-mutants and recA441 mutants caused a 50% reduction in AH50, when used in the amount of 6.4 X 10(7) and 2.6 X 10(7), respectively, the same degree of BH50 decrease was achieved with the amounts used equal to 1.1 X 10(8) and 4.3 X 10(6), respectively. C3 conversions caused by 4 X 10(8) cells in I ml of the normal human serum in the four strains tested accounted for 5-15%.     

Quantitative characterization of antagonistic activity of lactobacilli

In this work the method of serial dilutions of lactobacilli in two-layer agar was used. On the agar surface bacterial or fungal cultures were applied at different time intervals. A special quantitative characteristic was introduced. L. plantarum strain 8P-A3 was shown to have the maximum antagonistic activity. In great amounts L. casei and L. reuteri are capable to suppress the growth of bacteria and fungi. All lactobacilli under study produced a pronounced bactericidal effect on Pseudomonas, had different influence on the viability of Escherichia and staphylococci and exhibited fungistatic and fungicidal action only when inoculated at high concentrations.     

Impact of exogenic proteolytic enzymes on bacteria]

The impact of papain, trypsin and the enzyme complex vobenzyme on formation of biofilms by grampositive and gramnegative bacteria was studied. The enzymes were shown to inhibit the biofilm formation. When applilied to the formed associations, the enzymes potentiated the effect of antibiotics on the bacteria located in them. An increase in the antimicrobial effect of various nonrelated antibiotics was not connected with a change in the bacteria susceptibility but likely resulted from higher bioavailability of the drugs in the presence of the enzymes.     

Changes in virulence of Enterobacteriaceae in the presence of sub-inhibitory levels of antibiotics

The effect of subinhibitory concentrations of antimicrobial agents such as chloramphenicol, tetracycline, rifampicin and nalidixic acid on various factors of virulence in Shigella spp. and enteroinvasive colon bacilli was studied. It was shown that under such conditions changes took place in various events of the interaction with the epithelial cells, i.e. in adhesion, penetration, intracellular multiplication and transfers between contacting cells. The total effect of chloramphenicol resulted in increasing of the virulence while that of nalidixic acid, tetracycline and rifampicin resulted in its decreasing.     

The effectiveness of antibiotics on bacteria in biofilms

Bacteria can form different types of communities, united by common notion: biofilms. The aim of the present study was to determine the capacity of different antibiotics to penetrate into biofilms and act on unrelated bacteria. The study revealed that the formation of barriers between the community and the environment on artificial biofilms occurred in all strains of unrelated Gram-positive and Gram-negative bacteria used in this investigation. The capacity of antibiotics to penetrate into biofilms varied in different strains of the same species. For certain antibiotics similarity in their penetrating capacity was found to exist with respect to biofilms of unrelated bacteria. The penetration of antibiotics into mixed biofilms depended on the strain which determined its minimal value, so that the protection of one microorganism by another was thus observed. The method for the evaluation of the effectiveness of antibiotic penetration into bacterial biofilms, suitable for use in bacteriological laboratories, is proposed.