Preliminary investigations of microbiologically influenced corrosion of 304 stainless steel by anaerobic Clostridioides difficile biofilm

Clostridioides difficile is a pathogenic anaerobe that potentially causes microbiologically influenced corrosion (MIC). Coupons of 304 stainless steel (SS) were incubated with C. difficile in deoxygenated brain heart infusion supplement medium. After a 7-d incubation, C. difficile biofilms were observed on the 304 SS coupon surfaces. The sessile cell count on 304 SS coupons were (1.9 ± 0.5) × 10⁷ cells/cm². It was found that this high-grade SS did not suffer measurable corrosion weight loss and pitting. X65 carbon steel was used to verify C. difficile bio-corrosivity. A 7-d weight loss of 0.9 ± 0.2 mg/cm² was found on X65 coupons with the same incubation condition, which manifested as uniform corrosion. 13%Cr steel, also known as 420 SS which is a low-grade SS that is prone to pitting, was used to verify pitting by C. difficile. A 15.2 μm pit was observed after 26 d of incubation. Electrochemical tests were conducted in a 10 mL biofilm/MIC test kit. The electrochemical analysis of electron mediator injection indicated that MIC of 304 SS by C. difficile belongs to extracellular electron transfer-MIC. A 100 ppm (w/w) tetrakis (hydroxymethyl)phosphonium sulfate (a green biocide) injection test proved that it is a suitable disinfectant for C. difficile.