Role of microalgae in reducing antibiotic-resistant bacteria in synthetic wastewater

The increasing prevalence of antibiotic-resistant bacteria (ARB) and the widespread dissemination of antibiotic resistance genes (ARGs) in aquatic environments pose significant challenges to both public health and ecological integrity. This study investigates the potential of microalgae as a biological treatment strategy to limit the spread of ARB and the transfer of ARGs in synthetic wastewater (SWW). A multidrug-resistant Escherichia coli strain was introduced into SWW under two experimental conditions: one exposed to a single antibiotic and the other to multiple antibiotics. In both conditions, microalgae exhibited early and sustained suppression of ARB growth, initiating as early as 6 h post-treatment and significantly reducing bacterial populations, achieving a 0.4-0.6 log reduction in ARB within 72 h (p = 0.012-0.017). In contrast, untreated systems showed rapid ARB proliferation. Notably, antibiotic-sensitive bacterial (ASB) colonies reappeared in microalgae-treated condition after 48 h, despite being nearly undetectable in untreated controls by 24 h, suggesting that microalgae may either hinder ARG propagation or promote a reversion to antibiotic sensitivity. These findings highlight the dual role of microalgae as a bioremediation agent and a potential barrier to ARG transmission, offering a sustainable and eco-friendly approach to enhancing wastewater treatment and combating the spread of antibiotic resistance.