Type 304 stainless steel, copper containing stainless steel, and oxygen free copper were subjected to antibacterial tests and short term exposure experiments in a laboratory. Antibacterial tests showed that the copper containing stainless steel, as well as oxygen free copper, was antibacterial, yet the antibacterial activity of the copper containing stainless steel was lower than that of the oxygen free copper. In short term exposure experiments, the copper containing stainless steel, as well as type 304 stainless steel, didn't sterilize planktonic bacterial cells, while the oxygen free copper reduced the number of alive planktonic bacterial cells. The copper containing stainless steel did not protect itself from bacterial adhesion, but sterilized about 75 % of sessile bacterial cells and reduced formation of biofilms on its surface. Such experimental results indicate that the copper containing stainless steel is effective against biofilm related impacts.KEY WORDS: antibacterial stainless steel; copper; bacterial attachment; biofilm; microbiologically influenced corrosion; biocorrosion. 133© 2010 ISIJ spores and vegetative cells, and the functions were not reduced by dissolved organic substances. 26) In this paper, copper was selected as the antibacterial agent because of its higher bactericidal function comparative to silver. 27) Bacterial attachment and initiation of biofilms on a copper containing stainless steel surfaces were studied. Experimental Sample Materials and Preparation of SpecimensSample materials subjected to experiments were type 304 stainless steel (SS), copper containing stainless steel (Cu-SS) (MSSAM3, Nisshin Steel Co., Ltd., Tokyo, Japan) and oxygen free copper (OFC). Copper concentration in the Cu-SS was 3.78 mass%. As the phase of the Cu-SS was austenite, type 304 stainless steel was selected as a reference stainless steel. The chemical compositions of the sample materials are summarized in Table 1.Coupon specimens for antibacterial tests, 25 mmϫ25 mmϫ1 mm, were machined from supplied plates. The surfaces of specimens were polished by #1500 emery papers to obtain uniform surface finish. The polished specimens were subjected to ultrasonic cleaning in 70 % ethanol solution followed by drying and sterilization under ultraviolet (UV) ray illumination in a clean bench. Steam sterilization was not employed for sterilization of specimens because the steam sterilization process could make oxide layer and change chemical properties of the sample metal surfaces.Poly-ethylene (PE) films used in antibacterial tests were cleaned, sterilized and dried in the same manner as those for the specimens.For exposure experiments, coupon specimens with the size of 12.5 mmϫ12.5 mmϫ1 mm were used. Except the size of specimens, the preparation processes of specimens for exposure experiments was the same as that employed for the preparation of the specimens subjected to antibacterial tests. InoculumBacteria used in this study were Pseudomonas sp. The bacteria were isolated from a water system where MIC was suspecte...