Comparative assessment of antimicrobial efficacy of new potential biocides for treatment of cooling and ballast waters

The comparative in vitro antibacterial activity of five non-oxidizing biocides was investigated by laboratory standard test procedures. Minimum Inhibitory Concentrations (MIC) of two alkylated naphthoquinone derivative molecules (MNB and MPB) and three commercial biocide formulations (MACROTROL®MT200, MICROTREAT®AQZ2010 and MICROBIOCIDE®2594) were determined against a total of 23 non-pathogenic bacterial strains. This investigation demonstrated a broad-spectrum bactericidal efficacy of three of the assayed biocides (MT200 and both naphthoquinone derivatives) at low use levels, also against naturally tolerant species, such as Pseudomonas spp. MT200 was the most effective, inhibiting bacterial growth of both Gram-positive (MIC < 4 mg/l) and Gram-negative bacteria (MIC < 16 mg/l), whereas effectiveness of naphthoquinones was highly variable (MIC ranging from 1 to 64 mg/l). The findings show the ability of the tested products to reduce bacterial populations under laboratory conditions. These products could provide an efficient bacterial growth control, for treatment of both fresh and salt waters used for various industrial purposes.