Environmental strains potentially contribute to the proliferation and maintenance of antibiotic resistance in drinking water: A case study of Cupriavidus metallidurans

Highlights: • Fitness cost of an environmental multi-resistant strain was investigated. • Cupriavidus metallidurans strain is a robust resident in drinking water. • Megaplasmids of C. metallidurans are latent resistance gene pools. • metallidurans contributes to antibiotic resistance prevalence in drinking water. • metallidurans has high tolerance to chlorine and chloramine. Fitness costs of antibiotic resistance detrimentally affect the fate of resistance carriers. Intriguingly, numerous antibiotic resistant bacteria (ARB) have been detected despite the low concentration of antibiotics in drinking water. To reveal the causes of this discrepancy, we investigated the fitness cost of antimicrobial resistance in strain Cupriavidus metallidurans CR2 which was isolated from a drinking water filter. Pure culture and 1:1 competitive experiments were established at different nutrient levels. The growth rates of strain C. metallidurans CR2 significantly decreased when pure cultured under poor nutrient conditions, however, the multi-resistance and the resistance megaplasmids were well maintained. Competitiveness costs were observed in C. metallidurans when separately co-cultured with environmentally-isolated Flectobacillus BS1 and Pseudomonas sp. S3, while C. metallidurans was outnumbered by the rivals with a decrease of 1–2 logs. But the majority of C. metallidurans retained the plasmids under oligotrophic conditions even after 144 h (1.99 and 0.199 mg C/L). Additionally, C. metallidurans CR2 has a higher tolerance to chlorine and chloramine, which potentially could become prevalent in the subsequent distribution systems other than drinking water treatment plant. As a potential pathogen, the prevalence of Cupriavidus metallidurans in drinking water would also pose certain threats to human health.