Salinity as a modulator of antibiotic resistance in the environment: Patterns and mechanisms

Antibiotic resistance is recognized as one of the significant threats to global public health. Microorganisms, which serve as hosts and vectors for antibiotic resistance genes (ARGs), are ubiquitous in natural ecosystems and respond dynamically to environmental changes. Among various abiotic stressors, salinity has drawn growing attention as both a natural and anthropogenically influenced factor that can significantly shape microbial communities and resistance profiles. To date, however, evidence on the salinity–antibiotic resistance relationship remains fragmented and lacks comprehensive synthesis. In this review, we systematically analyzed 46 studies that specifically investigated this relationship across diverse environmental media. These studies employed diverse detection methods, including metagenomic and culture-based approaches, which differ in the coverage and clinical relevance of resistance information. The outcomes varied, with negative correlations between salinity and resistance reported most frequently, followed by variable results, and only a few studies documenting positive or non-significant associations. To explain these patterns, we further examine potential mechanisms through which salinity may influence ARG prevalence, including selective pressure on microbial individuals and communities, modulation of horizontal gene transfer, osmoregulation-linked responses, co-expression of salinity and antibiotic resistance, and interactions with other environmental factors. Finally, this synthesis highlights key knowledge gaps and outlines future research directions necessary to understand the role of salinity in shaping antibiotic resistance dynamics under changing environmental conditions.