Characterization of Antimicrobial Resistant Bacteria in Different Stages of a Wastewater Treatment Facility

Karen Sem

Authors:  Karen Sem, Katherine Y. Deliz Quiñones, PhD

Faculty Mentor: Katherine Y. Deliz Quiñones, PhD

College:  Herbert Wertheim College of Engineering


Most secondary and tertiary treatments currently implemented in wastewater treatment facilities (WWTFs) remove chemical and biological pollutants but may select for antimicrobial resistance (AMR) in surviving species. Reuse of reclaimed water and biosolids can propagate drug resistance genes throughout the environment, threatening public health and food security. The effect of different treatment stages on AMR selection can be determined by assisting changes in the occurrence and abundance of ARB in each stage of a facility. In this study, wastewater samples were collected from a WWTF receiving water from residential, research, and clinical facilities. Bacterial groups isolated from wastewater inoculated on selective and differential agar plates were characterized by morphology and biochemical tests and exposed to inhibitory concentrations of antibiotics to test for resistance. Most bacterial groups present throughout all stages of treatment were facultatively anaerobic and had decreased susceptibility to broad-spectrum antibiotics. This information can contribute to the development of more effective treatments and management strategies that target the removal of these emerging contaminants from wastewater.

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11 Responses
  1. quinn zacharias

    Tell me if I got this right? You wanted to see if there were antibiotic resistant bacteria in the waste water treatment facility at UF. The answer so far seems to be yes.

    1. Karen Sem

      Thank you for stopping by!

      Yes, our project revolved around the detection of antibiotic resistant bacteria in WWTFs. However, our main focus was not whether these ARBs were present in effluent, but instead at what stages of treatment they were present, which would tip us off to potential mechanisms for their removal.

      So far, we’ve found that ARBs are present in both wastewater treatment facilities examined in this study. However, while they seem to be removed by the final chlorination stage in WWTF2 (on campus), they are still present in the final effluent of WWTF1.

  2. Karen Sem

    Thank you for stopping by!

    Yes, we were trying to detect the presence of antibiotic resistant bacteria (ARBs) in WWTFs. Our main focus is not to find whether ARBs are present in effluent, but to find out where they are selected for/against in different treatment stages.

    We’ve found pathogenic ARBs in the treatment system. While they seem to be removed by chlorination in WWTF 2 (on campus), they are still present in effluent in WWTF 1 (a municipal facility).

  3. Christian Bedwell

    Hello Karen!

    In your future work, you mention using the 16S/ITS kit. Can you tell me about that process, and what it would allow you to figure out?

    1. Karen Sem

      Hello Christian!

      In 16S/ITS, a wastewater sample would be analyzed for specific genes that, prior to running metagenomic sequencing, must be individually selected for and stored in a library. Selected genes would be amplified so that their relative abundance amongst all genes detected in the sample can be found.

      In this project, by identifying the bacterial strains present in wastewater, we can narrow down the types of genes that we’d have to add to our library. Running 16S/ITS would allow us to identify the exact species of pathogenic bacteria (and other microbes, like fungi or viruses) present in the wastewater but also the drug resistance genes that they carry.

  4. Marina Curtis

    In your opinion, could public health be better improved by more controlled handling of semi-treated wastewater until the ARBs are removed in the final treatment staged, or by treatment for ARBs at an earlier stage in the process?

    1. Karen Sem

      Hello Marina, thanks for stopping by!

      From the literature review conducted for this study, it seems that the spread of antibiotic resistance through wastewater can best be mitigated by selecting for their removal earlier in treatment. Removal of residual antibiotics prior to secondary treatment would be a good method to reduce selection for antibiotic resistance amongst microbial communities present in later stages. Removal of any antibiotic resistant bacteria and genes present after secondary treatment could be removed by alternating disinfection processes, which select for different kinds of ARBs. However, this approach would be much more costly and thus difficult to implement than upfront processes.

  5. Christopher Cuevas

    Hi Karen, great job on your poster!

    Given the public health risks posed by antibiotic resistant bacteria, is removing them a priority for WWTFs? If so, what methods are they using to remove them during or after stages of treatment where they are most likely to form?

    1. Karen Sem

      Hello Christopher, thank you for stopping by!

      Since most surviving antibiotic resistant bacteria are opportunistically pathogenic and thus post the greatest health risk to individuals that are immunocompromised, I think their removal is not an immediate priority. ARBs are often selected for in WWTFs due to pressure from residual antibiotics, so the best method of prevention would be by removing these antibiotics prior to secondary treatment (granular activated carbon or even the introduction of fats have been proposed as potential solutions). Removal during secondary treatment is hard to accomplish since operating conditions must support the growth of microbial communities during these stages, so removal of ARBs would be highest during disinfection processes.