Bacterial infections can cause various dangerous diseases and conditions, including the necrotic Buruli ulcer, found most commonly in Africa. When antibiotics were introduced as treatment for many bacterial infections, great strides were made in reduction of morbitity and mortality. In recent years, however, some of these bacteria have become resistant to the antibacterial nature of these drugs, resulting in very dangerous infections such as MRSA (methicilline resistant Staphylococcus aureus). A new method of treating bacterial infections may be emerging through the use of French clays.
In 2001, a French humanitarian in the Ivory Coast began treating patients with Buruli ulcer with a poultice made from clay minerals. One of these, CsAg02, has been shown to be bactericidal against the following bacteria: E. coli, ESBL E. coli, S. enterica, P. aeruginosa, and M. marinum. It has about a 1000 fold reduction effect on these bacteria: S. aureus, PRSA, MRSA, and M. smegmatis, compared to normal growth. The bacteria chosen for this study are those recommended for testing of antimicrobials in the lab, with the exception of M. marinum, which was chosen because of it's close DNA similarity to Mycobacterium ulcerans (which cause Buruli ulcers).
The cause of the bactericidal effect of CsAg02 is yet to be determined, although the physical properties of clay (such as suffocating the bacteria, etc) seem to be ruled out. One thing that was looked at were several elements such as iron, barium and strontium which are in high concentrations in this clay mineral. However, when tested independently on these bacteria, the each element seems to actually increase growth. This is assumed to occur because these elements are needed for cell growth and may be a limiting factor in typical growth medium (broth or solid agar), instead of interfearing with cellular processes by inhibiting transport mechanisms or substituting as coenzyme factors.
It seems that the creation of an inhospitable environment may be the key mechanism that kills bacteria. A proposed idea along these lines is that the transition metals present in clay minerals take part in reactions that release free radicals. These free radicals, when in the presence of oxygen, can cause oxidative stress on the bacterial cells, killing them. Although not yet fully understood, the use of clay minerals may become part of antibacterial treatment in the future.