Report 3. Opportunistic Pathogens: Legionella pneumophila and Mycobacterium avium.
During our recent sampling trip to Flint, we found that all of our samples sites were free of fecal indicator bacteria but that many sites lacked a chlorine residual, which is a critical barrier for preventing regrowth of bacteria in pipes. Our research team has further observed in previous work that opportunistic pathogens tend to grow in distribution system and home plumbing pipes when there is a lack of chlorine residual. Thus, it is worrisome that recent reports in Genesee County indicate a possible increase in cases of Legionnaire’s Disease, a respiratory infection caused by an opportunistic pathogen (Legionella pneumophila).
During our trip, we collected samples from nine businesses located throughout the city of Flint, including eight of Flint’s designated monitoring sites and a business located in close proximity to the drinking water treatment plant, and seven homes of Flint water consumers. For comparison, we also collected water from four businesses that receive water from Detroit. At each of these sites we collected both water samples and swabs of bacteria growing on the surface within the faucet, known as the biofilm.
From these samples, we investigated the presence of two key opportunistic pathogens which are important to public health: Legionella pneumophila and Mycobacterium avium. We also measured the presence of a DNA marker specific to all bacteria within the Legionella genus. This Legionella genus is a category of bacteria which includes several pathogenic (e.g. Legionella pneumophila) and several non-pathogenic species.
Results: We did not detect quantifiable levels of Legionella pneumophila or Mycobacterium avium in water or biofilm samples collected from any of the sixteen sites in Flint or in any of the four sites receiving Detroit water.
We detected bacteria belonging to the Legionella genus in water collected from two of the nine businesses/monitoring sites and in five of seven citizen homes. Legionella genus was not detected in any of the four samples collected from sites receiving Detroit water.
Conclusion: We found no evidence of Legionella pneumophila or Mycobacterium avium present at the time of sampling at the sites tested. However, we hypothesize that the presence of bacteria belonging to the Legionella genus may be indicative of conditions in the distribution system or in the plumbing of tested homes that may be favorable to the growth of the pathogenic species, Legionella pneumophila. In particular, the chronically low levels of a chlorine residual in many parts of the distribution system are likely to increase the risk of opportunistic pathogen colonization.
Additional Notes: The method we used to quantify these pathogens is called quantitative polymerase chain reaction (or qPCR). It works by detecting DNA specific to the target microorganisms, making the method very specific, but also very sensitive, as an organism does not necessarily need to be alive or culturable for us to identify that it is present. The minimum threshold of target bacteria, or more accurately the bacteria’s DNA that must be present in the 1-liter samples that we collected is 10 DNA copies per mL or 104 copies in the entire swabbed biofilm. This is the best available and most sensitive method of Legionella detection.
Sample analyses and write-up: Emily Garner
Acknowledgements: Dr. Marc Edwards and Dr. Amy Pruden