Occurrence of plasmid pBI143 in wastewater in Baltimore

• Plasmid pBI143 was monitored in wastewater over a year in Baltimore County, USA. • pBI143 was detected in 100% of the samples. • Similar concentration of pBI143 compared to crAssphage. • Significant positive correlation between pBI143 and crAssphage. • pBI143 is a potential fecal and normalization marker. An ideal fecal and normalization marker for water quality monitoring or wastewater-based epidemiological studies should be globally abundant in wastewater and exhibit minimal seasonal variation. This study investigates the occurrence of novel fecal marker plasmid pBI143 in wastewater and compares its concentration with that of crAssphage in wastewater in Baltimore County, Maryland, USA. Forty-eight wastewater samples were collected from two wastewater treatment plants (WWTP) A and B in January to December, 2024, concentrated using a filter membrane with 0.45 μm pore size, and subjected to quantitative polymerase chain reaction. Both pBI143 and crAssphage were detected in 100% (48/48) of the samples. The average concentration of pBI143 was 8.2 ± 0.7 log 10 copies/L in WWTP A and 8.1 ± 1.0 log 10 copies/L in WWTP B. No significant difference between concentration of pBI143 and crAssphage was observed (paired t -test, p > 0.05). A significant correlation (ρ = 0.60, p < 0.05) was found between pBI143 and crAssphage, indicating similar characteristics between the two and the potential use of pBI143 as a fecal and normalization marker. Future research should focus on the prevalence of pBI143 in wastewater from non-industrialized countries, as well as validation of pBI143 as a human-specific fecal marker, prior to its universal application as a human-origin fecal and normalization marker.