A Virulent Strain of Salmonella enterica Serovar London Isolated in Infants with Enteritis Traced by Active Surveillance and Molecular Epidemiological Study

A total of 74 isolates of Salmonella enterica serovar London were collected through the Laboratory-Based Diarrheal Diseases Surveillance in 2000-2001. In order to characterize the isolates and investigate the source of the epidemic, we performed antimicrobial susceptibility tests and XbaI Pulsed-field gel electrophoresis (PFGE) of 44 Salmonella London isolates. Forty isolates were from feces of infants and four isolates were from adults aged 30, 52, 54, and 59 yr. Two subtypes were identified: a tetracycline-susceptible A 0 PFGE pattern and a tetracyclineresistant A 1 PFGE pattern. Interestingly, the isolates from all infants and one 30-yr-old adult were A 0 PFGE pattern and tetracycline-susceptible. Furthermore, the A 0 PFGE pattern strain was approximately 2 times more virulent than the A 1 PFGE pattern strain, according to the results of in vitro invasion assay using J774A.1 macrophage-like cells. These results indicate that the active surveillance with molecular epidemiological tools would be valuable for promptly finding new epidemic strains. Our results also suggested that the virulent Salmonella London strain might infect the infants through a common contaminated source.

Ovalbumin fused with diphtheria toxin protects mice from ovalbumin induced anaphylactic shock

For those with allergy, vaccination with a specific allergen has often been used as a major therapeutic measure. However, the universal application of this technique in clinics have been restricted due to its low success rates and the risk of active systemic anaphylactic shock (ASAS). In this regard, we constructed a fusion protein (OVA-DT), ovalbumin (OVA) fused with diphtheria toxin protein (DT), which may exert a specific cytotoxicity to cells bearing OVA-specific IgE. Its therapeutic effect was evaluated in mice (BALB/c) sensitized with OVA (Os-mice). OVA challenges to the OVA-sensitized mice (Os-mice) caused ASAS to death within 30 min, but OVA-DT treatment afforded mice complete protection. When OVA-DT was treated to the Os-mice, none showed the signs of ASAS when re-challenged 48 h after the treatment. OVA-DT itself was not found to be toxic or allergenic in normal mice. The effect of OVA-DT on the biological functions of mast cells was also studied. Binding of OVA-DT to OVA-specific IgE bearing mast cells and the inhibition of histamine release from these cells were observed. In addition, OVA-DT treatment inhibited the proliferation of OVA-specific B cells in mice. In Os-mice treated with OVA-DT, levels of anti-OVA IgG2a in serum and the production of IFN-gamma by splenic lymphocytes were found to increase, but the production of IL-4 by these cells decreased. Re-direction of cytokine profiles from OVA-specific Th2 to OVA-specific Thl is suggested. These results indicate that OVA-DT can protect Os-mice from ASAS due to OVA challenge, because it inactivates OVA-specific IgE-expressing cells, including mast cells and B cells.

Serological Immunity to Diphtheria among Korean Population / 감염

BACKGROUND: Diphtheria epidemics in Russia have spread to all the other independent states of the former Soviet Union and East European countries around 1990s. One of the most important measures in preventing diphtheria is to maintain high levels of immunity in the population. We studied the diphtheria antibody levels of 1,086 participants to investigate herd immunity in Korea. METHODS: The tested 1,086 serum specimens were collected from healthy individuals from September 1995 to March 1996. Diphtheria antitoxin titers were measured by a micro cell culture method using Vero cells. Antibody titer of 0.01 IU/ml to neutralize diphtheria toxin is an internationally accepted protective level. RESULTS: We studied the diphtheria antitoxin titer levels of 1,086 cases consisting of 579 males and 507 females. The proportion of protective antitoxin level to diphtheria is 69.2%. Diphtheria antitoxin levels showed no significant difference between males and females. The highest seropositive rate was observed in the 5 to 9-year old age group(95.8%). The seropositivity rate declined with age. The lowest seropositive rate was observed in the 20~39 years of age, maximally 43.4 %. Over 40 years of age, the seropositive rates increased again. CONCLUSION: The antibody titers in the Korean population declined from 95.8% to below 50% with age in the 1~39 year-old age group. To maintain the rate of population with protective antibodies to diphtheria, we recommend Td booster immunization to adults with low antitoxin titers and continuous survey for antitoxin titers.