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Researchers from Austria and Russia have developed an oral vaccine comprised of bacterial ghosts, or empty bacterial envelopes, which may protect against E. coli in animals and humans. Their findings appeared in the August 2005 issue of the journal Infection and Immunity.
Enterohemorrhagic Escherichia coli (EHEC) is a bacterial pathogen associated with several life threatening diseases in humans. O157:H7, one of the most harmful and frequently studied strains of the bacteria can cause intestinal inflammation ranging from diarrhea to hemorrhagic colitis, with more severe cases afflicting children and the elderly. EHEC O157:H7 has also been identified as a bioterrorism agent. There is currently no specific treatment against EHEC infection and antibiotics are not recommended as they prompt the liberation of toxins which can worsen the clinical course of the disease.
Because the major reservoir for EHEC O157:H7 is cattle, researchers are focusing on a vaccine that will prevent infection in both humans and animals. In order to mimic the bacterias natural route of infection they developed an oral vaccine in hopes of eliciting local immunity in the gut.
In the study, production of the protein E-mediated lysis was controlled to produce EHEC bacterial ghosts, or non-living bacterial cell envelopes. They have the same surface components of live cells and are capable of inducing strong immune responses, but the lack of genetic material inhibits transfer of resistance genes. An oral vaccine containing the bacterial ghosts was administered to mice that were challenged with a lethal dose of the EHEC strain 55 days later. A single dose of the vaccine resulted in an 86 percent protection rate and mice receiving a booster after 28 days showed a 93 percent survival rate. Non-immunized mice challenged with the bacteria had a 26 to 30 percent rate of survival.
Bacterial ghosts as candidate vaccines and carriers of foreign viral and/or bacterial antigens are under development as multivalent vaccines against diarrheal diseases of humans and might represent new, improved nonliving bacterial vaccines with excellent safety properties and high immunological potential, say the researchers.
Reference: U.B. Mayr, C. Haller, W. Haidinger, A. Atrasheuskaya, E. Bukin, W. Lubitz, G. Ignatyev. 2005. Bacterial ghosts as an oral vaccine: a single dose of Escherichia coli O157:H7 bacterial ghosts protects mice against lethal challenge. Infection and Immunity, 73. 8: 4810-4817.
Source: American Society for Microbiology