Spores ferry vaccines

Edible dormant bacteria protect against tetanus.

29 April 2003

HELEN PEARSON

In hard times some bacteria form tough dormant spores. © S.Cutting

Chomping on bacteria might protect people from infections, say British scientists. The next-generation edible vaccines could combat tetanus, anthrax and diarrhoea.

To survive hard times, the harmless bacteria Bacillus subtilis goes into a dormant spore form. Simon Cutting, of Royal Holloway University near London, and his colleagues have genetically engineered the microbe to carry a gene for one of the paralyzing toxins normally produced by tetanus bacteria.

When starved, the microbes make tough spores coated in the toxin. Seven out of eight mice that swallowed or inhaled these spores survived a lethal dose of tetanus, equivalent to a human infection¹.

Spores should be better than the existing tetanus shot, says Cutting, which requires refrigeration, sterile injections and ten-year boosters. These problems partly explain why as many as a million people are still affected by the disease annually, mostly in developing countries.

The technique "has promise", agrees Dennis Hruby of vaccine-development company SIGA Technologies in Corvallis, Oregon. It sidesteps the cost and complication of many vaccines, in which a bacterial or viral protein is purified and injected alongside an adjuvant - a protein that whips up the immune system.

Many people are working on next-generation vaccines to replace unsatisfactory ones or to negate the need for needles. Some, like Hruby, are using live, genetically modified bacteria instead of spores. "The challenge is to figure out how to deliver these safely and effectively," he says.

Others hope to grow transgenic bananas or potatoes that produce traces of vaccinating proteins in their cells. But fruit and vegetables can rot. Bacterial spores are cheap and hardy - they've been known to survive for as long as 28 million years.

Cutting is now making trial spore vaccines against the traveller's diarrhoea bug Escherichia coli and the potential bioterror agent anthrax. Existing anthrax immunization, which is effected by a crude cocktail of proteins, requires at least six shots, often causes soreness and is given only to military personnel.

1. Duc, L.H., Hong, H.A., Fairweather, N., Ricca, E . & Cutting, S. M. Bacterial spores as vaccine vehicles. Infection and immunity, 71, 2810 - 2818, (2003). |Article|