A survey of antibiotic-resistant bacteria in a sewage treatment plant in Thibodaux, Louisiana, USA

• Many antibiotic-resistant bacteria were identified.
• Fecal coliform bacteria were less in the treated sewage compared to raw sewage.
• Free DNA with antibiotic-resistant trait is being released from sewage treatment plant.
• Bacterial genetic transformation is occurring in passing on the antibiotic-resistant genes to the native bacteria in the sewage discharge point.

Antibiotic resistance is becoming a very large problem throughout the world. Antibiotics are used as prescribed medications to fight infections and prevent secondary bacterial infections during primary viral infections; they are also included in feeds for livestock and poultry. After passing through the human or animal body the antibiotics enter into the wastewater treatment process, where water is processed and cleaned and then returned to the environment. During sewage treatment, antibiotics come in contact with bacteria entering the treatment process, as well as bacteria used in the treatment process. The bacteria exposed to these antibiotics can become resistant during the treatment process and then expose the resistance genes to the environment upon release of treated water from the plant. Bacteria can become resistant via several mechanisms, including spontaneous mutation, induced mutation, genetic transformation, conjugation, and transduction. Because of the contact between bacteria and antibiotics during the treatment process, sewage plants are considered prime habitat to create antibiotic-resistant bacteria. There was a lack of research documenting the changes and flow of resistance between the stages of the wastewater treatment process or the possibility of uptake of resistant DNA in the environment into which the treated water is released. Therefore, this work was conducted to study the prevalence of antibiotic-resistant bacteria in various stages of sewage treatment. The results show the presence of antibiotic-resistant bacteria in raw sewage, as well as treated sewage. The results also indicate the possible release of antibiotic-resistant free DNA into the final discharge point in the nearby wetland.