Anti‐infectious activity of synbiotics in a novel mouse model of methicillin‐resistant Staphylococcus aureus infection

The anti‐infectious activity of synbiotics against methicillin‐resistant Staphylococcus aureus (MRSA) infection was evaluated using a novel lethal mouse model. Groups of 12 mice treated with multiple antibiotics were infected orally with a clinical isolate of MRSA at an inoculum of 10⁸ CFU on day 7 after starting the antibiotics. A dose of 400 mg/kg 5‐fluorouracil (5‐FU) was injected intraperitoneally on day 7 after the infection. A dose of 10⁸ CFU Bifidobacterium breve strain Yakult and 10 mg of galactooligosaccharides (GOS) were given orally to mice daily with the antibiotic treatment until day 28. The intestinal population levels of MRSA in the mice on multiple antibiotics were maintained stably at 10⁸ CFU/g of intestinal contents after oral MRSA infection and the subsequent 5‐FU treatment killed all the mice in the group within 14 days. B. breve administration saved most of the mice, but the synbiotic treatment saved all of the mice from lethal MRSA infection. The synbiotic treatment was effective for the treatment of intestinal infection caused by four MRSA strains with different toxin productions. There was a large difference among the six Bifidobacteria strains that were naturally resistant to the antibacterial drugs used. B. breve in combination with GOS is demonstrated to have valuable preventive and curative effects against even fatal MRSA infections.     

Epidemiological and serological survey of brucellosis in Mongolia by ELISA using sarcosine extracts

Brucellosis is an important zoonosis, and serological surveillance is essential to its control. However, cross-reactions of attenuated live cells of Brucella abortus strain S-19 and B. melitensis strain Rev-1 with Yersinia enterocolitica O9 or vaccinated animal sera interfere with accurate serological diagnosis by the Rose Bengal test (RBT). Therefore, we used ELISA with sarcosine extracts from the virulent B. abortus strain 544 to eliminate false-positives among RBT positive-sera. A total of 697 serum samples were collected in Mongolia from humans and animals in 23 nomadic herds. The herds were classified into three groups as brucellosis-endemic (BE), brucellosis-suspected (BS), or Brucella-vaccinated (BV). The number of 295 animals (43.0%) was positive by RBT, but 206 (69.8%) of these were positive according to ELISA; therefore, 30.2% of the RBT-positive sera were found to be false positives. The false positive samples for RTB represent 4.1%, 27.4%, and 68.2% of the animals from the BE, BS, and BV herds, respectively. In addition, 32% of RBT-positive human sera were also false positives. Thus, our ELISA would be more specific than RTB and useful for epidemiological surveillance for brucellosis.     

Protective effect of Bacillus anthracis surface protein EA1 against anthrax in mice

Bacillus anthracis spores germinate to vegetative forms in host cells, and produced fatal toxins. A toxin-targeting prophylaxis blocks the effect of toxin, but may allow to grow vegetative cells which create subsequent toxemia. In this study, we examined protective effect of extractable antigen 1 (EA1), a major S-layer component of B. anthracis, against anthrax. Mice were intranasally immunized with recombinant EA1, followed by a lethal challenge of B. anthracis spores. Mucosal immunization with EA1 resulted in a significant level of anti-EA1 antibodies in feces, saliva and serum. It also delayed the onset of anthrax and remarkably decreased the mortality rate. In addition, the combination of EA1 and protective antigen (PA) protected all immunized mice from a lethal challenge with B. anthracis spores. The numbers of bacteria in tissues of EA1-immunized mice were significantly decreased compared to those in the control and PA alone-immunized mice. Immunity to EA1 might contribute to protection at the early phase of infection, i.e., before massive multiplication and toxin production by vegetative cells. These results suggest that EA1 is a novel candidate for anthrax vaccine and provides a more effective protection when used in combination with PA.     

Variation in nitrogen isotopic composition in the Selenga river watershed, Mongolia

The stable nitrogen (N) isotope ratio (??¹⁵N) has been used to examine the anthropogenic N input (i.e., septic water, wastewater, and manure) to aquatic ecosystems, because anthropogenic N generally has a ??¹⁵N signature distinct from that found in nature. Aquatic organisms and the derived organic matter such as sediments are reported to become increasingly enriched in ¹⁵N as the human population density increases in watersheds. However, little is known about the relationship in steppe ecosystems, where the livestock population is greater than that of humans. Here, we conducted a preliminary study in the Selenga river mainstream watershed in Mongolia, which covers an area of approximately 300,000?km². A multiple regression analysis revealed that the ??¹⁵N of the riverine sediment was significantly affected by the human population density and more significantly by livestock population density. The population density, including both humans and livestock, significantly influenced ??¹⁵N of the macrophytic Potamogeton spp. The results showed that ??¹⁵N of riverine organic matter can be an indicator of the human and livestock population density, which is likely associated with the status of N cycles in livestock-dominated watersheds.