The present study reports on the role of the bacterium Serratia marcescens ACE2 in the corrosion behavior of carbon steel API 5L-X60 in diesel-water systems. The effect of commercial corrosion inhibitor (CI) on the growth of strain ACE2 and its corrosion inhibition efficiency was investigated. The corrosion rate was evaluated using electrochemical impedance spectroscopy (EIS) and polarization techniques in the diesel-water interface systems. The amine and carboxylic acid based inhibitor gave better efficiency in the absence of strain ACE2 by suppression of both anodic and cathodic reactions. In the presence of the strain ACE2, the inhibitor suppressed the cathodic reaction more significantly than the anodic reaction. The electrochemical behavior of steel API 5L-X60 was correlated with the role of the adsorbed amine based compound and degraded product on the metal surface. The surface morphology of the coupons in the presence/absence of the inhibitor with ACE2 was observed by using atomic force microscopy (AFM) and revealed pitting corrosion. This basic study is useful for the development of new approaches for the detection, monitoring, and control of microbial corrosion in a petroleum product pipeline.