Bactericidal efficacy of elevated pH on fish pathogenic and environmental bacteria

Area of Science:

• Marine Biology
• Environmental Science
• Microbiology

Background:

• Ship ballast water is a primary vector for introducing nonindigenous species globally.
• Effective ballast water treatment is crucial to prevent ecological and economic damage from invasive species.
• Current treatment methods require enhancement to ensure comprehensive elimination of aquatic organisms.

Purpose of the Study:

• To evaluate the bactericidal efficacy of elevated pH levels (10.0-12.0) as a ballast water treatment method.
• To determine the required exposure durations for different pH levels to achieve complete bacterial kill.
• To assess the effectiveness against a range of Gram-negative and Gram-positive bacteria, including fish pathogens and IMO D2 Standard indicators.

Main Methods:

• Laboratory experiments were conducted using tryptic soy broth adjusted to pH 10.0-12.0 with sodium hydroxide (NaOH).
• Bacterial viability was assessed at various time points (0, 4, 12, 24, 48, and 72 hours) post-treatment.
• The study included fish pathogens (Aeromonas spp., Yersinia ruckeri, Edwardsiella ictaluri), common aquatic bacteria (Serratia spp., Pseudomonas fluorescens, Staphylococcus sp., Bacillus sp.), and indicator organisms (Vibrio cholera, Escherichia coli, Enterococcus faecalis).

Main Results:

• All tested bacteria were eradicated within 72 hours at pH 12.0 or lower.
• Exposure to pH 10.0 for 4 hours proved bactericidal for Vibrio cholera, Edwardsiella ictaluri, and some isolates of Escherichia coli and Aeromonas salmonicida subsp. salmonicida.
• Complete eradication was achieved at pH 10.0 within 12-24 hours for remaining strains of Aeromonas salmonicida subsp. salmonicida, Pseudomonas fluorescens, and Escherichia coli.

Conclusions:

• Elevated pH, particularly between 10.0 and 12.0, is a highly effective method for eliminating diverse bacterial populations in ballast water.
• Specific pH and exposure time combinations can be optimized for rapid and complete bacterial inactivation.
• High pH treatment presents a viable and potent strategy for ballast water management to mitigate the spread of aquatic invasive species.