Secret Government Test With Bright Microbes

Our San Francisco Bay Area microbial palette is in progress, and I wanted to share with you an interesting microbial story that has come out of our microbe hunting.

I've lived in the Bay Area for more than a decade now, but I grew up on the US East Coast. I don't recall any characteristic buildup in my bathroom drains growing up, but when I moved out here in my early 20s - and maybe didn't scrub the tub as much as I should have - I started to notice a pink slime developing around the drain, reminiscent of the Cat in the Hat’s pink bathtub ring. "Maybe it's this cheap apartment," I thought. "At least it's not black mold" (Which, incidentally, is its own story)

I mentioned it to a friend over drinks and he told me he was used to pink film showing up in his drains from time to time, even in nice apartments! He wasn't stressed about it - "Just scrub it down with a little bleach." Sure enough, it disappeared and I didn't think about it much again. Until we started building our Bay Area microbe palette.

This scum is actually Serratia marcescens, and it's commonly found in bathrooms. It thrives on phosphorus and fatty acids, which are rich in soap residues found in sink and shower drains (Notla GM, 2022). Serratia species are considered pathogenic, but, as we've discussed previously, the amount of bacteria present and the route of transmission are important factors contributing to an organism's ability to cause disease.. These microbes mostly cause infection through ingestion so unless you taste the pink film, the risk of infection is low (Public Health Agency of Canada, 2012). If you encounter a pink scum, wash your hands and clean the film up as soon as you can to ensure the lowest risk to your health. Another reason to not be overly worried is the adjective “opportunistic”, which means disease caused by Serratia is typically only seen in folks who are not in full health. This means Serratia is most dangerous in a hospital setting where people have conditions that give it an opportunity to cause disease while those who are healthy are generally safe (but don’t test your luck by getting some in your eye!) (Mahlen 2011) 

Unfortunately, this is not something that the US military understood in 1950 when they secretly sprayed a mist of Serratia marcescens bacteria over the Bay Area. For six days.

Until the 1950s, Serratia was considered harmless. Because of its brilliant red color, it was used to study microbial transmission (Mahlen 2011). This made it a natural fit for what was dubbed "Operation Sea Spray," an attempt to study the susceptibility of a big city like San Francisco to a biowarfare attack. By sampling 43 sites in the area they found that, in fact, the microbes had spread even beyond the city to all the surrounding suburbs (Thompson, 2015). So the experiment successfully proved its point - residents of these areas would have had drastically-increased exposure to these microbes.

Secretly exposing the unknowing population of a major city to microbes is probably not ideal in the best of cases, but the US military erred in believing that Serratia would be completely harmless. A week after the tests, 11 patients checked into Stanford University Hospital with urinary tract infections. One man, who was recovering from surgery, died from the infection (Wheat, 1951). It wasn't until 1976 that the military acknowledged these tests, but the Serratia seems to have persisted. While we found no further evidence of outbreaks due to respiratory transmission, there have been a few cases of medically-associated transmission. For instance, in 2004, an Emeryville company's entire stock of flu vaccine had to be destroyed due to Serratia contamination (Tansey, 2004).

In fact, because Serratia infections in hospitals were rare before the experiment in 1950, it's possible that this experiment fundamentally changed the microbial ecology in The Bay Area (Tansey, 2004). Maybe my first apartment's pink scum was part of the lineage produced by that US military test 70 years ago - proof that humans are also actors in our complex ecosystem.

References

1. Mahlen SD. 2011. Serratia Infections: from Military Experiments to Current Practice. Clin Microbiol Rev 24:755–791. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3194826/ 
2. Wheat, R. P. (1951). INFECTION DUE TO CHROMOBACTERIA. A M a Archives of Internal Medicine, 88(4), 461. https://doi.org/10.1001/archinte.1951.03810100045004 
3. Thompson, H. (2015, July 4). In 1950, the U.S. released a Bioweapon in San Francisco. Smithsonian Magazine. https://www.smithsonianmag.com/smart-news/1950-us-released-bioweapon-san-francisco-180955819/ 
4. Tansey, B. (2004, October 31). Serratia has dark history in region / Army test in 1950 may have changed microbial ecology. SF Gate. https://www.sfgate.com/health/article/Serratia-has-dark-history-in-region-Army-test-2677623.php 
5. Public Health Agency of Canada. (2012, April 30). Pathogen Safety Data Sheets: Infectious Substances – Serratia spp. Canada.ca. https://www.canada.ca/en/public-health/services/laboratory-biosafety-biosecurity/pathogen-safety-data-sheets-risk-assessment/serratia.html 
6. Notla GM. (2022, May 2). Facts About Serratia marcescens: The Pink Stuff in Your Toilet, Shower, or Sink. Notla Water Authorit. https://www.notlawaterauthority.org/post/facts-about-serratia-marcescens-the-pink-stuff-in-your-toilet-shower-or-sink 
7. Page, E. H., & Trout, D. B. (2001). The Role of Stachybotrys Mycotoxins in Building-Related Illness. AIHAJ - American Industrial Hygiene Association, 62(5), 644–648. https://doi.org/10.1080/15298660108984664 
8. Chang, C., Gershwin, M.E. The Myth of Mycotoxins and Mold Injury. Clinic Rev Allerg Immunol 57, 449–455 (2019). https://doi.org/10.1007/s12016-019-08767-4