Antimicrobial Resistance of Heterotrophic Bacteria in Drinking Water-Associated Biofilms

Antimicrobial resistance (AMR) is one of the major threats to human health and is becoming an environmental challenge for water resources too. Our study's aim was: to assess the AMR of heterotrophic bacteria in drinking water-associated biofilms against six clinically important antibiotics; to compare the prevalence of antibiotic resistant bacteria (ARB) in drinking water and in the associated biofilms; to estimate biofilm formation ability of selected isolates. Culture-dependent methods were used in the population-based study of the biofilms and in assessment of the single-species biofilm formation ability and the AMR phenotype of the isolated strains. The population proportion of the bacteria resistant to each tested antibiotic significantly differed in the biofilms formed in drinking water from different sampling points. In all biofilms, the abundance of tetracycline- and ampicillin-resistant bacteria was low, and of streptomycin-resistant bacteria was high. An increased proportion of the bacteria resistant to ciprofloxacin, chloramphenicol and streptomycin was detected in the biofilms compared to those found in the drinking water. The prevalence of ARB in the biofilms implies an impact on the drinking water quality and an assessment of the attached and the planktonic bacteria is needed to clarify the prevalence of AMR in the drinking water distribution system.

Automated summary

The study found significant differences in the proportion of antibiotic-resistant bacteria in biofilms formed in drinking water compared to those in drinking water, with an increased proportion of bacteria resistant to ciprofloxacin, chloramphenicol, and streptomycin in biofilms. This suggests that the prevalence of ARB in biofilms has an impact on drinking water quality and assessment of attached and planktonic bacteria is needed to clarify the prevalence of AMR in the drinking water distribution system.