Contribution of virus-induced lysis and protozoan grazing to benthic bacterial mortality estimated simultaneously in microcosms

In contrast to the water column, the fate of bacterial production in freshwater sediments is still a matter of debate. Thus, the importance of virus-induced lysis and protozoan grazing of bacteria was investigated for the first time simultaneously in a silty sediment layer of a mesotrophic oxbow lake. Microcosms were installed in the laboratory in order to study the dynamics of these processes over 15 days. All microbial and physicochemical parameters showed acceptable resemblance to field data observed during a concomitant in situ study, and similar conclusions can be drawn with respect to the quantitative impact of viruses and protozoa on the bacterial compartment. Viral decay rates ranged from undetectable to 0.078 h⁻¹ (average, 0.033 h⁻¹), and the control of bacterial production from below the detection limit to 36% (average, 12%). The contribution of virus-induced lysis of bacteria to the dissolved organic matter pool as well as to benthic bacterial nutrition was low. Ingestion rates of protozoan grazers ranged from undetectable to 24.7 bacteria per heterotrophic nanoflagellate (HNF) per hour (average, 4.8 bacteria HNF⁻¹ h⁻¹) and from undetectable to 73.3 bacteria per ciliate per hour (average, 11.2 bacteria ciliate⁻¹ h⁻¹). Heterotrophic nanoflagellate and ciliates together cropped up to 5% (average, 1%) of bacterial production. The viral impact on bacteria prevailed over protozoan grazing by a factor of 2.5–19.9 (average, 9.5). In sum, these factors together removed up to 36% (average, 12%) of bacterial production. The high number of correlations between viral and protozoan parameters is discussed in view of a possible relationship between virus removal and the presence of protozoan grazers.     

Adherence ability of Pseudomonas aeruginosa strains isolated from patients with cystic fibrosis to two different epithelial cell lines

The ability of 59 wild-type strains of Pseudomonas aeruginosa to adhere to the HeLa and Buffalo Green Monkey Kidney (BGMK) cells was investigated. Twenty strains were isolated from sputa of cystic fibrosis patients, while 19 strains were isolated from tracheal aspirates and 20 from bronchial secretions of patients without cystic fibrosis, and they were used as a control group of strains. The statistically significant difference between adherence ability of strains was observed (p < 0.01). While most of the tracheal and bronchial isolates were hyperadhesive (51-110 bacteria per cell) most of the cystic fibrosis isolates adhered poorly to the HeLa and BGMK cells (1-10 bacteria per cell). The bacterial binding to the cells was blocked when bacteria were incubated at 80 degrees C for 20 min before the adherence assay. These results indicate that alginate is not involved in the adherence of P. aeruginosa to the used epithelial cell lines, and, because of that, mucoid strains isolated from persistently colonized cystic fibrosis patients showed poor adherence ability.     

Mathematical modeling of vascular endothelial layer maintenance: the role of endothelial cell division, progenitor cell homing, and telomere shortening

Maintenance of the endothelial cell (EC) layer of the vessel wall is essential for proper functioning of the vessel and prevention of vascular disorders. Replacement of damaged ECs could occur through division of surrounding ECs. Furthermore, EC progenitor cells (EPCs), derived from the bone marrow and circulating in the bloodstream, can differentiate into ECs. Therefore, these cells might also play a role in maintenance of the endothelial layer in the vascular system. The proliferative potential of both cell types is limited by shortening of telomeric DNA. Accelerated telomere shortening might lead to senescent vascular wall cells and eventually to the inability of the endothelium to maintain a continuous monolayer. The aim of this study was to describe the dynamics of EC damage and repair and telomere shortening by a mathematical model. In the model, ECs were integrated in a two-dimensional structure resembling the endothelium in a large artery. Telomere shortening was described as a stochastic process with oxidative damage as the main cause of attrition. Simulating the model illustrated that increased cellular turnover or elevated levels of oxidative stress could lead to critical telomere shortening and senescence at an age of 65 yr. The model predicted that under those conditions the EC layer could display defects, which could initiate severe vascular wall damage in reality. Furthermore, simulations showed that 5% progenitor cell homing/yr can significantly delay the EC layer defects. This stresses the potential importance of EPC number and function to the maintenance of vascular wall integrity during the human life span.     

Anticancer activity for 4,4'-dihydroxybenzophenone-2,4-dinitrophenylhydrazone (A-007) analogues and their abilities to interact with lymphoendothelial cell surface markers

The structure of the anticancer agent 4,4'-dihydroxybenzophenone-2,4-dinitrophenylhydrazone (A-007) has been modified through SAR and by incorporating barbituric acid, pyridine, quinoline, and alkylcarboxylic acids into A-007's moieties. Analogue anticancer activity and interacting with CD surface markers on a T-cell leukemia cell line were evaluated and the correlation between SAR and biological properties are discussed.     

Genotyping of Human and Porcine Yersinia enterocolitica, Yersinia intermedia, and Yersinia bercovieri Strains from Switzerland by Amplified Fragment Length Polymorphism Analysis

In this study, 231 strains of Yersinia enterocolitica, 25 strains of Y. intermedia, and 10 strains of Y. bercovieri from human and porcine sources (including reference strains) were analyzed using amplified fragment length polymorphism (AFLP), a whole-genome fingerprinting method for subtyping bacterial isolates. AFLP typing distinguished the different Yersinia species examined. Representatives of Y. enterocolitica biotypes 1A, 1B, 2, 3, and 4 belonged to biotype-related AFLP clusters and were clearly distinguished from each other. Y. enterocolitica biotypes 2, 3, and 4 appeared to be more closely related to each other (83% similarity) than to biotypes 1A (11%) and 1B (47%). Biotype 1A strains exhibited the greatest genetic heterogeneity of the biotypes studied. The biotype 1A genotypes were distributed among four major clusters, each containing strains from both human and porcine sources, confirming the zoonotic potential of this organism. The AFLP technique is a valuable genotypic method for identification and typing of Y. enterocolitica and other Yersinia spp.     

N-acetylation of amino sugar methyl glycosides for gas-liquid chromatographic analysis.

A procedure is described for rapid and quantitative N-acetylation of amino sugars, particularly suitable for gas-liquid chromatographic analysis of constituent carbohydrates in glycoproteins.     

Prevalence of antibodies to porcine parvovirus in wild boars (Sus scrofa) in Croatia

Serologic evidence of exposure to porcine parvovirus (PPV) in the wild boar (Sus scrofa) in Croatia was investigated. Serum samples from 219 wild boars captured during 2003 from 12 different locations in the Republic of Croatia were tested by using a commercial enzyme-linked immunoassay (ELISA) and a hemagglutination inhibition (HI) test. Antibodies to PPV were detected in 91 (41.6%) of tested samples and positive results were detected in wild boar from all sample locations. Adults had a significantly higher prevalence (70%) than juveniles (31%; P < 0.01). Our results indicate that wild boar populations throughout the Republic of Croatia are exposed to PPV.     

Application of fluorescent amplified fragment length polymorphism for comparison of human and animal isolates of Yersinia enterocolitica

An amplified fragment length polymorphism (AFLP) method, developed to genotype Yersinia enterocolitica, has been used to investigate 70 representative strains isolated from humans, pigs, sheep, and cattle in the United Kingdom. AFLP primarily distinguished Y. enterocolitica strains according to their biotype, with strains dividing into two distinct clusters: cluster A, comprising largely the putatively pathogenic biotypes (BT2 to -4), and cluster B, comprising the putatively nonpathogenic biotype 1A strains and a single BT1B isolate. Within these two clusters, subclusters formed largely on the basis of serotype. However, AFLP profiles also allowed differentiation of strains within these serotype-related subclusters, indicating the high discriminatory power of the technique for Y. enterocolitica. Investigation of the relationship between strain AFLP profile and host confirmed that pigs are, and provides further proof that sheep may be, potential sources of human infection with putatively pathogenic strains. However, the results suggest that some strains causing human disease do not come from veterinary sources identifiable at this time. The distribution of some BT1A isolates within cluster A raises questions about the relationship between virulence potential and biotype.     

Stage conversion of Toxoplasma gondii RH parasites in mice by treatment with atovaquone and pyrrolidine dithiocarbamate

The mouse-virulent RH strain of Toxoplasma gondii is generally considered to have lost its cyst-forming capacity, and conversion of RH tachyzoites into cysts in non-immune mice has previously been shown exclusively following early treatment with sulfadiazine (SDZ). We here describe the development of tissue cysts in mice infected with RH strain parasites and treated with atovaquone (ATO) combined with pyrrolidine dithiocarbamate (PDTC). Groups of Swiss-Webster mice infected intraperitoneally (i.p.) with 10(2) RH tachyzoites were treated with 5, 25 and 100 mg of ATO/kg per day alone or combined with PDTC at 250 mg/kg per day from day 1 postinfection (p.i.) for 14 days. A total of 19 mice survived the 6-week observation period. Of these, brain cysts were recovered in nine (47%), with burdens ranging from 50 to 3120 (mean +/- S.D. = 622 +/- 963). All cyst-harboring mice had high specific IgG antibody levels (1:10,240-1:40,960, corresponding to 500-2000 IU/ml), as did one mouse in which cysts were not demonstrated, which was therefore included in the group of mice with residual infection. Bioassay performed to test the infectivity of these cysts produced acute lethal toxoplasmosis following i.p. inoculation in all instances (100%), and importantly, following peroral inoculation in four (29%). The recovered tachyzoites were highly infectious. In addition, significantly elevated interferon gamma (IFN-gamma) in the treated mice which developed residual infection compared with any group of infection-free (treated or subinoculated) mice, indicates immunological control of the parasite in the latent form. In conclusion, early treatment of mice infected with T. gondii RH tachyzoites with ATO and PDTC induces conversion into tissue cysts, thus providing a new model for studying the mechanism(s) of T. gondii stage conversion.