a bactericidal composition and method for inhibiting and controlling the growth of the capsulated , facultative bacterium , klebsiella pneumoniae , are disclosed . the composition comprises an amount , effective for the intended purpose of 3 - iodo - 2 - propynylbutyl carbamate and 3 , 4 - dichloro - 1 , 2 - dithiol - 3 - one . the method comprises administering between about 0 . 1 to about 200 parts of this combined treatment to the particular water containing system for which treatment is desired .