Thymidine phosphorylase activity and its relationship to trimethoprim in initial strains and thymidine-, thymine-dependent and trimethoprim-resistant mutants of plague microbe]

The comparative study revealed thymidine phosphorylase activity in the initial strains of a plague microbe of the field variety and in thymidine-, thymine-dependent and trimethoprim-resistant mutants of the plague microbe of other varieties. The data fully conformed to the results of the microbiological investigation of the strains' ability to grow on the nutrient media with trimethoprim in the presence of thymine and thymidine. On the basis of these results it appeared possible to divide the initial and mutant strains of the plague microbe into four arbitrary groups: initial strains of the plague microbe of all the varieties except the field ones sensitive to trimethoprim under any temperature conditions of incubation on any medium with any supplements; initial strains of the plague microbe of the field variety resistant to trimethoprim at 28 degrees C in the presence of thymine or thymidine alone; Tmpr mutants whose resistance to trimethoprim at 28 degrees C did not depend on the presence of thymine or thymidine, purine and vitamins, but depended on the presence of these substances at a temperature of 37 degrees C.     

Synergistic action of some antibacterial agents in studies on albino mice with experimental plague caused by Fr- phenotype strain of the plague microbe]

Possible use of ciprofloxacin combinations with some other antibiotics such as rifampicin, ampicillin, cefotaxime, doxycycline and amikacin was studied on albino mice with experimental plague caused by the pathogen strain (approximately 1000 LD50) deprived of the ability to produce the capsular antigen, fraction I (Fra- phenotype). The combination of ciprofloxacin with ampicillin or doxycycline had no effect on the increase of the survival rate (t<2) evident of inexpediency of its use in the infection caused by the Fra- strains of the plague microbe. The combination of ciprofloxacin and cefotaxime used in definite doses had some effect (t=2.6). The most significant synergistic effect was observed with the use of ciprofloxacin in combination with amikacin or rifampicin (t>3.3-9.0) which made the combination most promising.     

Spheroplasts of plague microbe strains from the Transcaucasian uplands and their capacity for pesticin synthesis]

Spherical formations of the plague microbe strains from the Transcaucasian Upland, I plague microbe strain of the sandwort variety and I strain of the marmot variety were obtained under the effect of lithium chloride. They had the remains of the cell wall, were viable, sensitive to osmotic shock, preserved sensitivity to the specific bacteriophage and pesticins. All this was evident of isolation of the spheroplasts of the plague microbe. The spheroplasts showed a capacity for pesticin production. The pesticin synthesis by the spheroplasts of the plague causative agent from the Transcaucasian Upland increased with an increase in the content of lithium chloride in the medium. The largest inhibiiton zones were observed, when 0.7-0.8 per cent of lithium chloride were present in the medium. In the spheroplasts of the plague causative agent from the Mountain Altai (the marmot variety) the pesticin synthesis was inhibited with an increase in the content of lithium chloride in the medium. The activity spectrum of the pesticins of the spheroplasts of the plague causative agent from the Transcaucasian Upland and the spheroplasts of the strains of the marmot and sandwort varieties was broader than that of the rod-like forms of these strains. The indicator properties were found in the strains of the plague microbe of the marmot and sandwort varieties with respect to the pesticins of the spheroplasts of the sel-like producing organisms and organisms from the Transcaucasian Upland.     

Experimental evaluation of prospects for the use of beta-lactams in plague infection caused by pathogens with plasmid resistance to penicillins]

High therapeutic efficacies of ceftriaxone, ceftazidime, cefotaxime and azthreonam in the treatment of experimental plague induced by beta-lactamase-producing strains of the plague microbe containing R plasmids RP-1, R57b and R40a were shown to correlate with their in vitro antibacterial activities. The therapeutic efficacy of sulbactam/ampicillin was recorded in the treatment of plague induced by the strain containing R plasmids R57b and R40a (the treatment course of 7 days). However, it was lower when the infection was due to the strain containing plasmid RP-1 (beta-lactamase TEM-2). Cefoperazone was not active in the treatment of experimental plague induced by the strains containing plasmids RP-1 and R57b (beta-lactamases TEM-2 and OXA-3). Ceftriaxone versus the antibiotics tested was considered to be the drug of choice for the etiotropic therapy of plague induced not only by the type strains of the plague microbe but also by its variants with the plasmid pattern resistance to penicillins.     

Study of trimethoprim sensitivity in strains of Yersinia pestis isolated from various natural foci of plague

The effect of exogenic addition of purines and pyrimidines on trimethoprim sensitivity was studied in 134 vaccinal and virulent strains of the plague causative agent isolated at various periods in 12 natural plague foci. 74 strains proved to be sensitive to low concentrations of trimethoprim in the cultivation media irrespective of the presence or absence of thymine or thymidine in them. In this respect the strains differed from many other bacterial species which in the presence of thymidine or thymine were resistant to high concentrations of trimethoprim. 60 natural arginine deficient strains of the plague causative agent from Transcaucasia and Mongolia showed high levels of resistance to trimethoprim on media with thymine or thymidine. The possible mechanism of the plague microbe sensitivity to trimethoprim in the presence of thymine or thymidine is discussed with an account of the literature and original data.     

Adhesion of Enterococcus faecalis 1131 grown under subinhibitory concentrations of ampicillin and vancomycin to a hydrophilic and a hydrophobic substratum

The effect of two subinhibitory antibiotic concentrations of ampicillin and vancomycin during growth on the adhesion of Enterococcus faecalis 1131 to glass and silicone rubber was studied in a parallel plate flow chamber. Initial deposition rates and numbers of adhering bacteria after 4 h were higher on hydrophilic glass than on hydrophobic silicone rubber, regardless of growth conditions. The presence of 1/4 minimal inhibitory concentration (MIC) of ampicillin during growth reduced enterococcal adhesion to both substrata, but growth in the presence of 1/4 MIC vancomycin did not affect the adhesion of E. faecalis. Moreover, enterococcal adhesion increased after growth in the presence of 1/8 MIC vancomycin. The increased adhesion after growth in the presence of subinhibitory concentrations of vancomycin may have strong implications for patients living with implanted biomaterials, as they may suffer adverse effects from use of this antibiotic, especially since bacteria once adhered are less sensitive to antibiotics.     

Iron assimilation by Yersinia pestis on iron-deficient media

The growth of plague bacteria may be limited by the level of iron concentration in the nutrient medium. The virulent strains of the plague microbe possess the more pronounced mechanism of iron assimilation as compared to the vaccine strain. The iron ions are extracted by the virulent and vaccine strains only under the cell surface contact with the iron-saturated transferrin. The iron-sorbing function is peculiar to the plague microbe cell walls which is pronounced more strongly in the virulent strains.     

Antibiotics shaping bacterial genome: deletion of an IS91 flanked virulence determinant upon exposure to subinhibitory antibiotic concentrations

The nucleoid-associated proteins Hha and YdgT repress the expression of the toxin α-hemolysin. An Escherichia coli mutant lacking these proteins overexpresses the toxin α-hemolysin encoded in the multicopy recombinant plasmid pANN202-312R. Unexpectedly, we could observe that this mutant generated clones that no further produced hemolysin (Hly(-)). Generation of Hly(-) clones was dependent upon the presence in the culture medium of the antibiotic kanamycin (km), a marker of the hha allele (hha::Tn5). Detailed analysis of different Hly(-) clones evidenced that recombination between partial IS91 sequences that flank the hly operon had occurred. A fluctuation test evidenced that the presence of km in the culture medium was underlying the generation of these clones. A decrease of the km concentration from 25 mg/l to 12.5 mg/l abolished the appearance of Hly(-) derivatives. We considered as a working hypothesis that, when producing high levels of the toxin (combination of the hha ydgT mutations with the presence of the multicopy hemolytic plasmid pANN202-312R), the concentration of km of 25 mg/l resulted subinhibitory and stimulated the recombination between adjacent IS91 flanking sequences. To further test this hypothesis, we analyzed the effect of subinhibitory km concentrations in the wild type E. coli strain MG1655 harboring the parental low copy number plasmid pHly152. At a km concentration of 5 mg/l, subinhibitory for strain MG1655 (pHly152), generation of Hly(-) clones could be readily detected. Similar results were also obtained when, instead of km, ampicillin was used. IS91 is flanking several virulence determinants in different enteric bacterial pathogenic strains from E. coli and Shigella. The results presented here evidence that stress generated by exposure to subinhibitory antibiotic concentrations may result in rearrangements of the bacterial genome. Whereas some of these rearrangements may be deleterious, others may generate genotypes with increased virulence, which may resume infection.     

Effect of subinhibitory concentrations of antimicrobials on meningococcal adherence

Meningococci adhere to human pharyngeal cells and agglutinate erythrocytes. These events are dependent upon pili and are reduced by encapsulation. The effect of subinhibitory concentrations of seven antimicrobials on meningococcal adherence, antimicrobials on meningococcal adherence, piliation, hemagglutination (HA), and bacterial proteins was studied to determine their potential for modifying virulence. Piliation was reduced by most antibiotics but was most markedly (greater than 70%) reduced by rifampin, tobramycin, and VCN (vancomycin, colistin, and nystatin). Bacterial proteins as determined by sodium dodecyl sulphate--polyacrylamide gel electrophoresis were altered: tetracycline, sulfamethoxazole, rifampin, and VCN caused loss of a 43-45 K protein and a general decrease in all stainable protein bands, while erythromycin, ampicillin, and tobramycin only caused an increase in a 28 K protein. HA was reduced by ampicillin, tobramycin, erythromycin, and VCN but interstrain variability was present. Epithelial cell adherence was diminished by an average of 45% compared to controls. The meningococcal strains lost HA, piliation, and adherence in the same rank order, however, there was no significant rank correlation of antibiotic inhibitory activities on these parameters. These results indicate that subinhibitory antibiotic concentrations reduce meningococcal piliation and alter other bacterial proteins; these changes are associated with diminished adherence and hemagglutination, alterations which may be markers of meningococcal virulence.     

The epizootiological significance of flea accumulation in aggregations of the female long-tailed suslik in the Tuva plague focus

The formation of aggregations of related females is a peculiarity of the intrapopulational organization of long-tailed suslik that results in the accumulation of Citellophilus tesquorum, the main vector and keeper of the plague microbe in the Tuva plague nidus. The plague agent is adapted to the existence on the territory occupied by aggregations of females that manifests itself in the delay of the beginning and prolixity of block-formation periods in fleas. The transfer of the agent from one place to another takes place only at the high abundance of long-tailed suslik. When the number of the suslik is low the plague microbe circulates in the ranges of one or several neighbouring aggregations of females having no possibility for successful transfer to a new place.     

Doxycycline in the prevention of experimental plague induced by plague microbe variants]

A comparative study was performed on the efficacy of doxycycline in experimental plague infection induced in albino mice by strain 231 of the plague microbe and its variant 231 Fra- deprived of the ability to produce the fraction I antigen. It was shown that the LD50 for strain 231 during animal treatment with doxycycline was significantly higher than that for variant 231 Fra-. Prophylaxis of the plague infection caused by the Fra- forms of the plague microbe required significantly higher doses of doxycycline (ED50) than that of the infection caused by the Fra+ forms. The use of the daily maximum permissible doses of doxycycline (50 to 100 mg/kg a day) for 10 days in treatment of albino mice infected with the strain Fra- did not provide animal survival at the level higher than 60 to 70 per cent while the survival rate in the animals infected with the strain Fra+ of the plague microbe and treated according to the same scheme amounted to 90-100 per cent. The lower therapeutic efficacy of doxycycline in the treatment of the infection caused by the fractionless variant of the plague microbe should be considered in development of rational schemes for prophylaxis and treatment of plague.     

The epizootiological role of the population organization of the stock of fleas on the long-tailed suslik in a natural focus of plague in Tuva

Spatial location of epizootic events in the Tuva plague focus is determined at a considerable degree by the population structure of the flea Citellophilus tesquorum--the main plague microbe vector. Within the enzootic territory occupied by five populations of the long-tailed ground squirrel (Citellus undulatus) there are six populations of C. tesquorum. Each population of fleas has a corresponding autonomic plague focus. Various conditions for the microbe life activity in these populations are recovered. The circulation of the microbe is closely connected with certain intrapopulation groupings of fleas--the nuclei of populations.     

Chromosomal resistance of plague agent to quinolones]

The nature of increasing chromosomal resistance to quinolones was studied in a model of the plague microbe. Five virulent strains of the natural plague microbe (Y. pestis) were used in the experiment: 363 (1/1479), 231, 2385, 2442 and 2444. The one-stage procedure for isolation of the mutants was applied. It was shown that the frequency of the one-stage mutants resistant to oxalinic acid, pefloxacin and ciprofloxacin amounted to 10(-9)-10(-11) and was 2 to 3 orders of magnitude lower than that of the mutants resistant to nalidixic acid. Two types of the plague microbe mutants resistant to the quinolones were detected: those resistant to the quinolones to the generations (Nalr-phenotype) and those resistant to the representatives of the 3rd generation quinolones (Nals-phenotype). The quinolones were not efficient in the treatment of albino mice with experimental plague caused by the quinolone-resistant forms of the plague microbe.     

Factors influencing the expression in vitro of Candida albicans stress mannoproteins reactive with salivary secretory IgA

We have examined the influence of subinhibitory concentrations of several antifungals, the different glucose and ammonium sulphate concentrations in the culture medium as well as the strain variability on the expression in vitro of stress mannoproteins reactive with salivary sIgA in C. albicans and other Candida spp isolates. Irrespective of the conditions used, no reactivity with salivary sIgA was observed in yeast cells grown at 25 °C. However, when grown at 37 °C, all of the 10 C. albicans strains, but only 9 out 28 non-C.albicans isolates studied showed reactivity with salivary sIgA. Cells grown at 37 °C in medium containing maximum concentrations of glucose and ammonium sulphate expressed the antigens reactive with sIgA during longer periods of time than the cells grown in medium with minimal concentrations of the same compounds. The regulatory role showed by the concentration of glucose and ammonium sulphate on the antigenic expression was subordinated, nevertheless, to the most important factor, the temperature of incubation. Only isolates showing low susceptibility expressed the antigens reactive with sIgA under the influence of subinhibitory concentration of antifungals. However, induced resistance to one of the antifungals tested (5 fluorocytosine) allowed the antigenic expression at elevated subinhibitory concentrations even in previous susceptible strains. In conclusion, in addition to the temperature, factors such as characteristics of the strain, the concentration of glucose and ammonium sulphate in the culture medium and the resistance to antifungals played a role on the expression of C. albicans antigens reactive with sIgA, which could be of clinical relevance in the course of infection.This revised version was published online in October 2005 with corrections to the Cover Date.     

Pathogenic action of the plague microbe on the flea Xenopsylla cheopis and the ultrastructure of the causative agent at various times of its stay in the vector

Pathology of gastro-intestinal tract of Xenopsylla cheopis fleas infected with plague microbe was determined by means of electron microscopy. Ultrastructure of plague microbe during different periods of its stay in the vector was studied.     

Sensitivity of different strains of the causative agent of plague to disinfectants]

Various strains of the plague microbe was found to have statistically significant differences in their sensitivity to phenol, formaldehyde and chloramine. These differences did not correlate with the origin, virulence and nutritional requirements of the plague strains. The sensitivity of the plague microbe to formaldehyde and phenol was found to be related to the permeability of its cell wall.     

Detoxifying effect of antibiotics and their effectiveness in experimental plague at the stage of explicit intoxication]

The effect of antibiotics such as amikacin, rifampicin, doxycycline, polymyxin B and cefotaxime on the toxins of the plague microbe (lipopolysaccharide + fraction II according to Beiker) was studied in vitro and in vivo. The study on the antibiotic neutralization of plague toxins revealed that only polymyxin had toxin neutralizing capacity which depended on the dose. Investigation of the polymyxin effect at various stages of plague infection showed that when polymyxin in a dose of 1250 units and a mixture of plague toxins in lethal doses were administered simultaneously to albino mice, the positive effect amounted to 100 per cent. When the antibiotic was administered 30 or 60 minutes later, the antibiotic efficacy proved to be lower by 90 or 76.6 per cent, respectively. The intoxication in later periods (in 90-120 minutes) resulted in a decrease in animal survival up to 40-15 per cent. It was demonstrated on the model of the plague infection in albino mice that the use of amikacin, cefotaxime, rifampicin or doxycycline during polymyxin therapy at the stage of marked generalization of the infection provided a significant increase in the animal survival (60 to 80 per cent) as compared to that after the use of the same drugs alone (0 to 20 per cent).     

Efficiency of Neopsylla abagaitui fleas as plague vectors in Transbaikalia

Experiments have shown that the block of proventriculus develops in 1.1 to 1.5% of individuals of the flea Neopsylla abagaitui infected with plague microbe. These insects transmit the agent during bloodsucking to different plague carriers (Citellus dauricus, C. undulatus, Meriones unguiculatus, Microtus gregalis). The plague microbe is preserved in fleas for 65 days (the observation period).     

Host Aspect of Territorial Expansion of the Plague Microbe Yersinia pestis from the Populations of the Tarbagan Marmot (Marmota sibirica)

Biology Bulletin - Based on ecological studies, the concept of synchronous polytopic speciation of the plague microbe Yersinia pestis from the psychrophilic saprobiontic pseudotuberculosis microbe,...