Tips from the journals of the American Society for Microbiology
Genetic Link Identified in Human and Avian E. coli May Suggest Zoonosis
A group of international researchers have identified common virulence factors in strains of Escherichia coli collected from infected humans and chickens suggesting that avian E. coli may be a potential human pathogen. Their findings appear in the October 2006 issue of the Journal of Clinical Microbiology.
Pathogenic strains of E. coli O18:K1:H7 (ExPEC) are implicated in a range of infections in humans such as neonatal meningitis, septicemia, urinary tract infections and pneumonia. Avian E. coli pathogens (APEC) are also believed to cause urinary tract infections in cats and dogs, septicemia in calves and pigs, and systemic colibacillosis in birds. Previous studies have shown similarities between APEC and ExPEC strains but no research to date has been devoted to the comparison of specific strains for common virulence factors and genetic relationships.
O18:K1 strains are frequently isolated from humans infected with neonatal meningitis and septicemia as well as chickens with colibacillosis. The K1 capsule is a key facilitator in circumventing host defenses. IbeA, the virulence factor commonly associated with human neonatal meningitis, is also preferential in O18:K1 APEC strains. In the study twenty-two ExPEC isolates of human origin and thirty-three of avian origin were monitored and compared for their virulence factors and lethality in chicks. Both avian and human isolates proved lethal for chicks while demonstrating similar virulence patterns, one of which was identified in 75% of the isolates.
"The results obtained with the O18:K1:H7 E. coli strains that we have studied here show that various but closely related clones can be recovered from extraintestinal infections in humans and chickens," say the researchers. "Epidemiological studies are required to demonstrate if they have evolved independently or if cross-contamination between human and avian communities is possible, leading to a hypothesis that avian colibacillosis due to O18:K1:H7 strains could be considered a zoonosis."
(M. Moulin-Schouleur, C. Shouler, P. Tailliez, M.R. Kao, A. Bree, P. Germon, E. Oswald, J. Mainil, M. Blanco, J. Blanco. 2006. Common virulence factors and genetic relationships between O18:K1:H7 Escherichia coli isolates of human and avian origin. Journal of Clinical Microbiology, 44.10: 3484-3492.)
Newly Identified Antibody May Neutralize Inhalation Anthrax Toxin
A newly identified antibody capable of neutralizing the inhalation anthrax toxin in rabbits and monkeys may offer an alternative method of preventing and treating infection in humans say US researchers. Their findings appear in the October 2006 issue of the journal Infection and Immunity.
The intentional use of Bacillus anthracis, the causative agent of anthrax, continues to pose serious threat as a bioterrorism or biowarfare agent. Although vaccines currently available are highly effective, multiple doses are required therefore necessitating antibiotic therapy for those individuals exposed prior to scheduled completion.
Monoclonal antibodies (MAb) are derived from one clone of cells, recognize only one antigen (the protective antigen (PA) component of the anthrax toxin combines with the lethal factor for cell entry) and are described as highly specific and purified. In the study the fully human MAb (now recognized at MAb 1303) was selected after neutralizing the anthrax toxin in transgenic mice. MAb 1303 was then found to offer effective postsymptomatic treatment in rabbits exposed to aerosolized anthrax spores as well as serve as a protective agent in monkeys challenged with aerosolized anthrax spores following a single intramuscular injection.
"Selection of an anti-PA MAb by using a functional assay that is a surrogate for protection has resulted in the identification of a fully human MAb with potent activity in vivo and uncovered a previously unrecognized mechanism of antibody-mediated toxin neutralization that is important for currently used anthrax vaccines," say the researchers.
(L. Vitale, D. Blanset, I. Lowy, T. O'Neill, J. Goldstein, S.F. Little, G.P. Andrews, G. Dorough, R.K. Taylor, T. Keler. 2006. Prophylaxis and therapy of inhalational anthrax by a novel monoclonal antibody to protective antigen that mimics vaccine-induced immunity. Infection and Immunity, 74.10: 5840-5847.)
New Antibody-Based Treatment May Facilitate Mother-to-Child Antiretroviral Immunity
A new study suggests that mothers may be able to transfer antiretroviral immunity during gestation and while breastfeeding when receiving a new antibody-based treatment say researchers from France. They report their findings in the October 2006 issue of the Journal of Virology.
Monoclonal antibodies (MAb) are now the largest class of engineered proteins in the medical field, with 19 already approved by the FDA for human use. With more than 400 others involved in human clinical trials researchers are looking to apply this new therapeutic format to cancer and immune defects, as well as infectious diseases.
The FrCas (E) retrovirus is a neurodegenerative disease that led to death within 1 to 2 months when mice were infected at 5 to 6 days old. In the study researchers investigated whether the antibodies from MAb 667-treated mothers with strong anti-FrCas (E) immune responses could affect the immune systems of their FrCAS (E) infected pups following placental and/or breastfeeding transfer. Results showed reduction in the viral load and protective antiviral response from breastfeeding alone as well as placental transfer. Researchers also found that placental transfer protected animals infected neonatally and initiated a neutralizing anti-FrCas (E) response.
"Our data support the concept that passive immunotherapies during late gestation and/or breastfeeding might help retrovirally infected neonates prime their own protective immune responses, in addition to exerting an immediate antiviral effect," say the researchers.
(L. Gros, M. Pelegrin, M. Plays, M. Piechaczyk. 2006. Efficient mother-to-child transfer of antiretroviral immunity in the context of preclinical monoclonal antibody-based immunotherapy. Journal of Virology, 80.20: 10191-10200.)
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