a container assembly provided with an antibacterial agent against “ slow - leak ” bacteria , comprising a container such as a plastic bottle which has a mouth portion having a rim ; and a seal member such as a crown cap fitted to the mouth portion at the rim , wherein at least either a surface portion of the rim or the rim - contacting surface portion of the seal member includes an antibacterial agent such as silver zeolite in the form of a coating or a liner , thereby effectively blocking the entry of unwanted live bacteria and eumycetes which may enter the interior of the container assembly due to slow - leak .