A study of action of subinhibiting concentrations of antibiotics on the expression of genes regulating production of pathogenicity factors in Burkholderia cepacia and Pseudomonas aeruginosa

Described in the paper are the results of a study of differential expression of pathogenicity of B. cepacia and P. aeruginosa in subinhibiting concentrations (SIC) of cyprofloxacyne. While identifying genes expressing differentially in the antibiotic SIC, genes cepR B. cepacia and P. aeruginosa expressing without cyprofloxacyne in the cultivation medium and not expressing in the antibiotic SIC were detected. Finally, involvement of cepR B. cepacia in regulating the pathogenicity expression factors according to "quorum sensing" is under discussion.     

Molecular genetic typing of methicillin-resistant Staphylococcus aureus strains, isolated in hospitals of different regions of the Russia and Belarus

The study of the length of the amplification products of the coagulase gene with the subsequent restriction analysis (the method of PCR--restrictive fragment length polymorphism, or RFLP) was used for typing 90 S. aureus strains. Among the strains under study, 78 were methicillin-resistant S. aureus (MRSA) strains, including 74 obtained in 1986 - 2002 in hospitals of different cities of the Russia and Belarus, as well as epidemic strains EMRSA-1, -2, -3, -12, obtained from the National Laboratory of Health, London (UK). The use of this method made it possible to type all the strains under study, which were differentiated into 9 groups by means of endonuclease Sfo1 and 7 groups by means of Alu1. Majority of clinical MRSA strains, belonged, according to the type of restriction, to groups 4 and 5. The study of the coagulase gene by the method of PCR - RFLP made it possible: to analyze the epidemic situation in hospitals for a period of several years; to compare the properties of strains isolated in different hospitals; to establish the genetic relationship of strains, isolated in 1998 - 2002, with strains, isolated in 1986 - 1990. The results of the study suggest that at least two epidemic MRSA strains, genetically similar to international strains, circulate in hospitals of Russia.     

The influence of bacteria of the Burkholderia cepacia and Pseudomonas aeruginosa complex on cell-mediated immune reactions in experimental animals

The evidence has been obtained that various species, as well as individual strains having pathogenicity factors, produced different effect on the functional activity of immunocompetent B and T lymphocytes of mice infected intraperitoneally. The injection of live P. aerruginosa PA 103 and B. cepacia 8240 cells resulted in imunosuppression of antibody-forming cells, synthesizing antibodies to heterologous antigens. On the contrary, in the animals infected with B. cepacia 8236 the functional activity of B lymphocytes increased. An increase in the proliferative activity of spleen cells was noted in the presence of T and B mitogens after the infection of mice with P. aeruginosa PA 103 in comparison with B. cepacia 8236 and B. cepacia 8240 which produced a faintly pronounced modulating effect. The pathogenesis mechanisms of infections induced by these microorganisms as well as the development of chronic, persisting forms of the infectious process are discussed.     

The toxin-producing capacity of populations of Vibrio cholerae of different origins

As the result of the study of toxin formation in 165 V. eltor strains having different virulence, most of the virulent cultures have shown stable toxin production, though 5-10% of their colonies have proved to be nontoxigenic. In faintly virulent strains toxin production was found to be unstable, which is indicative of the heterogeneity of their population composition as regards their capacity for toxin formation. The population of avirulent strains consists mainly of nontoxigenic clones (95.7%).     

L-citrulline supplementation reverses the impaired airway relaxation in neonatal rats exposed to hyperoxia

Background

Hyperoxia is shown to impair airway relaxation via limiting L-arginine bioavailability to nitric oxide synthase (NOS) and reducing NO production as a consequence. L-arginine can also be synthesized by L-citrulline recycling. The role of L-citrulline supplementation was investigated in the reversing of hyperoxia-induced impaired relaxation of rat tracheal smooth muscle (TSM).

Methods

Electrical field stimulation (EFS, 2–20 V)-induced relaxation was measured under in vitro conditions in preconstricted tracheal preparations obtained from 12 day old rat pups exposed to room air or hyperoxia (>95% oxygen) for 7 days supplemented with L-citrulline or saline (in vitro or in vivo). The role of the L-citrulline/L-arginine cycle under basal conditions was studied by incubation of preparations in the presence of argininosuccinate synthase (ASS) inhibitor [α-methyl-D, L-aspartate, 1 mM] or argininosuccinate lyase inhibitor (ASL) succinate (1 mM) and/or NOS inhibitor [N^ω-nitro-L-arginine methyl ester; 100 μM] with respect to the presence or absence of L-citrulline (2 mM).

Results

Hyperoxia impaired the EFS-induced relaxation of TSM as compared to room air control (p < 0.001; 0.5 ± 0.1% at 2 V to 50.6 ± 5.7% at 20 V in hyperoxic group: 0.7 ± 0.2 at 2 V to 80.0 ± 5.6% at 20 V in room air group). Inhibition of ASS or ASL, and L-citrulline supplementation did not affect relaxation responses under basal conditions. However, inhibition of NOS significantly reduced relaxation responses (p < 0.001), which were restored to control level by L-citrulline. L-citrulline supplementation in vivo and in vitro also reversed the hyperoxia-impaired relaxation. The differences were significant (p <0.001; 0.8 ± 0.3% at 2 V to 47.1 ± 4.1% at 20 V without L-citrulline; 0.9 ± 0.3% at 2 V to 68.2 ± 4.8% at 20 V with L-citrulline). Inhibition of ASS or ASL prevented this effect of L-citrulline.

Conclusion

The results indicate the presence of an L-citrulline/L-arginine cycle in the airways of rat pups. L-citrulline recycling does not play a major role under basal conditions in airways, but it has an important role under conditions of substrate limitations to NOS as a source of L-arginine, and L-citrulline supplementation reverses the impaired relaxation of airways under hyperoxic conditions.     

Parasexuality in Race 65 Colletotrichum lindemuthianum Isolates

ABSTRACT. Heterokaryosis is the initial step of the parasexual cycle, a process that provides genetic variability in filamentous fungi through the production of heterozygous diploid nuclei. To characterize the parasexual cycle in Colletotrichum lindemuthianum, we evaluated the presence of heterokaryosis, vegetative compatibility reactions, and diploid formation among isolates of Race 65 collected from different Brazilian states. Vegetative compatibility groups were identified among the isolates according to their ability to form heterokaryons. Two heterozygous diploids were selected from compatible heterokaryons, which were characterized by the segregation of the parental auxotrophic markers and by RAPD profiles.     

Characteristics of the heat-stable enterotoxin of NAG vibrios

Cell-free culture filtrate boiled for 15 minutes has been found to retain its biological activity in various experimental models used for the determination of the toxicogenicity of cholera vibrio filtrates. During gel filtration of the concentrated filrate o. NAG vibrio, strain NO. 9852, through Sephadex G-75 toxic activity could be detected in the free volume of the column, which was indicative of the fact that the molecular weight of the thermostable enterotoxin was about 70,000 daltons and greater. The methods of gel diffusion and aggregated hemagglutination have been used to show that the thermostable enterotoxin of NAG vibrio No. 9852 is immunologically unrelated to cholerogen. Some data obtained in experimental models suggest that the thermostable enterotoxin probably differs from cholera enterotoxin in the mechanism of its action.