Previously, a factor(Factor T) was found in aged mixtures of tungstate and phosphate, which greatly sensitizes strains of methicillin-resistant Staphylococcus aureus to β-lactams. Factor T was purified and identified as undecatungstophosphate([PW₁₁O₃₉]⁷⁻). Undecatungstosilicate([SiW₁₁O₃₉]⁸⁻), a compound closely related to undecatungstophosphate, showed a similar enhancing effect. Chemically, these compounds are classified as " polyoxotungstates ", and it is expected that these tungsten compounds will be useful as a " tool " in laboratory tests : i.e., in screening media for highly resistant MRSA strains. They may be also useful to investigate the resistant mechanism of the bacterial cells.