Computational study of solution behavior of magainin 2 monomers.

Antimicrobial peptides (AMPs) play crucial role as mediators of the primary host defense against microbial invasion. They are considered a promising alternative to antibiotics for multidrug resistant bacterial strains. For complete understanding of the antimicrobial defense mechanism, a detailed knowledge of the dynamics of peptide-membrane interactions, including atomistic studies on AMPs geometry and both peptide and membrane structural changes during the whole process is a prerequisite. We aim at clarifying the conformation dynamics of small linear AMPs in solution as a first step of in silico protocol for establishing a correspondence between certain amino-acid sequence motifs, secondary-structure elements, conformational dynamics in solution and the intensity and mode of interaction with the bacterial membrane. To this end, we use molecular dynamics simulations augmented by well-tempered metadynamics to study the free-energy landscape of two AMPs with close primary structure and different antibacterial activity - the native magainin 2 (MG2) and an analog (MG2m, with substitutions F5Y and F16W) in aqueous solution. We observe that upon solvation, the initial α-helical structures change differently. The native form remains structured, with three shorter α-helical motifs, connected by random coils, while the synthetic analog tends predominantly to a disordered conformation. Our results indicate the importance of the side-chains at positions 5 and 16 for maintaining the solvated peptide conformation. They also provide a modeling background for recent experimental observations, relating the higher α-helical content in solution (peptide pre-folding) in the case of small linear AMPs to a lower antibacterial activity.

[Data on the epidemiology of Lyme disease in Bulgaria]. / Materialy po épidemiologii bolezni Laima v Bolgarii.

134 patients with clinically, epidemiologically and serologically confirmed Lyme's disease have been examined. 89.5% of them had erythema chronicum migrans, 112 patients (83.6%) were known to have had tick bites. The majority of patients were white-collar workers and townspeople. Hungry ticks collected from plants were shown to contain B. burgdorferi. 497 foresters and animal farmers have been serologically examined, using an indirect immunofluorescence test. Antibodies to B. burgdorferi in diagnostic titres have been revealed in 15.3% of foresters and 17.8% of animal farmers.

[Characteristics of Proteus, Klebsiella, Enterobacter and Citrobacter strains isolated in urological infections]. / Kharakteristika shtammov rodov Proteus, Klebsiella, Enterobacter i Citrobacter, vydelennykh pri uroinfektsiiakh.

The comparative study of more than 300 Proteus, Klebsiella, Enterobacter and Citrobacter strains isolated from patients with urological infections and parenteral infections of other localization, as well as from the feces of healthy persons has been carried out. The strains causing inflammatory processes in the urinary tract have been shown to possess no strict specificity. The ability of opportunistic enterobacteria to cause urinary tract lesions is their polydeterminant property ensured by the combination of different factors. A number of characteristics which can be considered as the markers of "nephritogenic" strains have been revealed. Thus, among Proteus mirabilis strains the largest percentage is constituted by strains fermenting sucrose and producing hemolysin. The urological pathogenicity of "nephritogenic" strains belonging to the genera Proteus, Klebsiella and Enterobacter has been found to be linked with their resistance to complement and their capacity for producing substances increasing capillary permeability. In C. freundii strains differences in O serogroups and a number of markers (the fermentation of raffinose, the formation of hemolysin and permeability factor) have been revealed. These data may be useful for the prognosis and evaluation of the course of urological infections.

[Antibiotic resistance of uropathogenic strains of E. coli isolated from patients in the USSR and the People's Republic of Bulgaria]. / Antibiotikorezistentnost' uropatogennykh shtammov E. coli, vydelennykh ot bol'nykh v SSSR i NRB.

The MIC of benzylpenicillin, ampicillin, ceporin, streptomycin, kanamycin, gentamicin, tetracycline, rondomycin, rifampicin, chloramphenicol, nalidixic acid, orafuran, furacin and furazolidon with respect to E. coli strains isolated from urological patients were determined and compared with those isolated from patients with other localization of inflammatory processes and the feces of healthy persons. It was shown that the strains isolated from the urine of the urological patients were characterized by higher levels of the drug resistance and as a rule were polyresistant. The bacterial resistance was due to the presence of conjugative R plasmids in 26-32 per cent of the cases and nonconjugative R plasmids in 37-38 per cent of the cases. The total number of the cultures with the drug resistance controlled by the plasmid markers amounted to 64-69 per cent. Ceporin, gentamicin, and furacin had the highest inhibitory effect.