A highly prevalent and specific cryptic plasmid pBI143 for human fecal pollution tracking in a subtropical urban river

Microbial source tracking (MST) is a critical tool for identifying sources of human and animal fecal pollution in aquatic environments. To enhance human fecal pollution tracking, this study evaluated the performance characteristics of pBI143, a cryptic plasmid recently identified for potential MST applications. Nucleic acid samples from ten animal species were screened for pBI143, revealing its presence in a small number of pigs, cows, dogs, cats, and flying fox fecal samples. Despite minor cross-detection with non-human fecal samples, pBI143 exhibited a high specificity value (up to 0.93). In untreated urban wastewater, pBI143 was consistently detected in all samples, exhibiting higher concentrations than the well-established human Bacteroides HF183 marker gene. Following a wastewater discharge event, pBI143 concentrations were monitored in an urban river and correlated well with both HF183 and enterococci 23S rRNA marker genes. Using conditional probability analysis, the likelihood of human fecal pollution was estimated to be 89.3 % when pBI143 was detected in 50 % of the river water samples. This study demonstrates that pBI143 is a highly abundant and specific human fecal marker for tracking human fecal pollution in environmental waters. Monitoring of pBI143 could significantly improve the accuracy of human fecal source identification in environmental waters, offering valuable insights for public health risk management and pollution mitigation strategies.