Culturable macroplastic-associated potential human pathogens in coral reef lagoons, Madagascar

Area of Science:

• Marine microbiology
• Environmental science
• Public health

Background:

• Potentially human pathogenic bacteria (PHPBs) are found in marine plastic microbiomes, but their culturability and concentration on plastics are poorly understood.
• Assessing actual health risks requires data on viable PHPBs associated with marine plastics.

Purpose of the Study:

• To investigate the culturability and concentration of PHPBs on floating macroplastics in human-impacted reef lagoons.
• To compare PHPB levels on plastics versus surrounding seawater.

Main Methods:

• Collected 70 macroplastic and 20 seawater samples from southwestern Madagascar.
• Utilized selective media to culture and quantify PHPBs from plastic and water samples.
• Identified dominant PHPB species using culture-based methods.

Main Results:

• Four culturable PHPBs (Staphylococcus aureus, Escherichia coli, Enterococcus faecalis, Vibrio Harveyi clade) were identified on plastics and in seawater.
• 52% of plastic samples harbored multiple PHPB species; only 7% were PHPB-free.
• PHPB concentrations were significantly higher on macroplastics than in seawater, with the Vibrio Harveyi clade most abundant.

Conclusions:

• Floating macroplastics serve as reservoirs and fomites for viable PHPBs.
• Interpreting health risks requires contextualizing bacterial concentration data with exposure, persistence, and virulence factors.
• Solely relying on concentration data for risk assessment may lead to misinterpretation.