Acta Microbiologica Bulgarica

93-106

Authors: Stoyanova, A., Galabov, A. S.

Millions of people, mostly children, are infected annually by enteroviruses with a wide variety of clinical manifestations. Most enteroviral infections are inapparent (Modlin et al., 2001), i.e. these viruses circulate in the human population without being “spotted”. In a number of cases they cause clinically manifested illnesses of varying severity, including diseases affecting the central nervous system, heart, endocrine pancreas, etc. The high morbidity, the mortality rates in children and the high-risk groups (immunocompromised patients and newborns), as well as the lack of effective vaccines (excluding polioviruses) determine chemotherapy as the primary means of control of enteroviral infections. Up to now, no effective chemotherapeutic agents for specific treatment of such infections have been registered. A multitude of compounds have been tested, but only few of them are active in vivo. The substances that have reached clinical trial stages have adverse side effects, low selectivity, high toxicity or unfavorable pharmacokinetic properties, and are, therefore, not suitable for use in clinical practice. The main reason for the failure of the anti-enteroviral therapy is that enteroviruses become drug-resistant and even drug-dependent. This is due to the extremely high levels of mutation and recombination in these viruses, leading to heterogeneous mutant populations. One way to combat resistance is to develop approaches for combined application of new or already existing substances with different mechanisms of action. Our team was the first to introduce analysis of the combined effects of selective inhibitors of enterovirus replication with different mechanisms of action (Nikolaeva and Galabov, 1999, 2000, 2011). Furthermore, the process of development of resistance to the most effective enterovirus inhibitors – the WIN compounds – was studied. A panel of phenotype markers was also presented for characterization of drug-dependent mutants (Nikolova and Galabov, 2003; Nikolova et. al., 2011). In addition, a new highly effective approach has been developed for combined administration of anti-enteroviral substances for chemotherapy of coxsackievirus neuroinfection in newborn mice, which could serve as the basis for new therapeutic strategies. It consists in consecutive, alternating, not concomitant, application of the compounds in the combination (consecutive alternating administration treatment course, CAA course). Double, triple and quadruple regimens with some of the best studied anti-enteroviral inhibitors were tested. The highest activity was manifested by the triple combinations in consecutive administration of inhibitors with different mechanisms of action, applied in a strict order (Vassileva-Pencheva and Galabov, 2010; Stoyanova et.al., 2015).

115-117

Authors: Raynova, Y., Marchev, A., Doumanova, L., Pavlov, A., Idakieva, K.

Hemocyanins (Hcs) are oligomeric copper-containing proteins that function as oxygen carriers in the hemolymph of several mollusks and arthropods. In this study we present an investigation on the antioxidant activity of the Hc isolated from snails Helix aspersa maxima (HaH), using various experimental models. The free radical scavenging activity was determined against 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical and [2,2’-azinobis(3-ethylbenzothiazoline-6-sulfonic acid)] free radical cation (ABTS). Cupric ion reducing antioxidant capacity (CUPRAC) and Ferric-reducing antioxidant power (FRAP) assay also were carried out. The results obtained show that HaH exhibits good radical scavenging activity by 59.54% reduction of the DPPH and 62.31% inhibition of ABTS radicals. Furthermore, HaH demonstrated a strong chelating effect on copper ions measured through CUPRAC method. In conclusion, the present study revealed for the frst time the antioxidant properties of molluscan Hc. The antioxidative activity of HaH could probably involve quenching of reactive oxygen species and metal ion chelation, thereby reducing the potential of prooxidants to attack cellular components.

122-126

Authors: Gergova, R. T., Markovska, R. D., Mitov, I. G.

The following Moraxella catarrhalis strains were used in the experiments: eight beta-lactamase-producing clinical isolates and four isolates including a control strain 353 CCUG without beta-lactamase. The other strains used as controls in this procedure were two isolates of Staphylococcus aureus and two of Escherichia coli: beta-lactamase producers and non-producers control strains of S. aureus: ATTC 29213 and E. coli ATCC 25922. All of the microbial strains were tested with ampicillin alone and with ampicillin in combination with murine monoclonal antibody (MAb) 219 against lipooligosaccharide of M. catarrhalis in a 96-well plate to determine the minimal inhibitory concentration (MIC). The testing was performed by broth dilution method and minimal bactericidal concentration (MBC) on brain heart infusion agar (BHI). The effect of the combination of aminopenicillin with MAb219 was manifested as a fourfold reduction of the MIC and the MBC of the tested beta-lactamase producing M. catarrhalis. The effect over the control strains and moraxellae without beta-lactamase was either missing or there was a slight reduction of MIC and MBC. The conclusion of the study is that MAb219 in combination with ampicillin in in vitro testing can decrease resistance to aminopenicillins in M. catarrhalis after the linking of MAb219 with lipooligosaccharide of the outer membrane in the antigen-antibody complex.

132-140

Authors: Abrashev, R., Dolashka, P., Angelova, M.

The protective effect of pretreatment with low oxidative stress factors is little known in relation to the growth and development of filamentous fungi. The acquisition of new knowledge can be particularly useful for industrially important fungal strains. In the present study, the adaptive response of the filamentous fungus Aspergillus niger 26 to oxidative stress has been examined. The findings indicate that pretreatment with a sub-lethal temperature leads to the development of resistance to lethal concentrations of paraquat (PQ), H2O2 and extremely high temperatures. Fungal cultures subjected to 35°C followed by exposure to high doses of stress agents showed a higher amount of biomass accumulation compared to the single treated cells. The pre-exposure strategy exerted a protective effect with respect to the amount of oxidatively damaged proteins in A. niger cells, which was accompanied by a corresponding increase in the intracellular protein content and induction of antioxidant enzymes compared to the non-adapted cultures. At the same time, the results demonstrated different responses in the temperature-adapted cells. Pretreatment makes cells more resistant to both PQ and temperature than to H2O2.

145-148

Authors: Stoev, A., Kostadinov, G.

The paper presents an investigation aimed at identifying the zones with regular incidence of pear rust. Such zones are appropriate for testing of cultivar susceptibility to the pathogen and fungicidal efficacy. The investigation data indicate that the disease is common on the monitored pear trees grown in the skirts of the north slopes of mountain Vitosha. Further away from the mountain, in Sofia Valley, the rate of pear rust attack is lower or the infection is missing.