Serratia marcescens – Bacteria
Occasionally customers call to ask about a slimy pink substance that sometimes forms in moist
areas around their homes. They most frequently observe it in toilet bowls, on surfaces in shower
stalls and bathtub enclosures, inside dishwashers, on tiles, in sinks, and in pet water dishes.
A red or pink pigmented bacterium known as Serratia marcescens is thought to be the cause of
the pink “stuff’. Serratia bacteria are common inhabitants of our environment and can be found in
many places, including human and animal feces, dust, soil, and in surface waters. The bacteria
will grow in any moist location where phosphorous containing materials or fatty substances
accumulate. Sources of these substances include soap residues in bathing areas, feces in toilets,
and soap and food residues in pet water dishes. Many times, the pinkish film appears during and
after new construction or remodeling activities. Others have indicated the pink “stuff’ occurs
during a time of year that their windows are open for the majority of the day.
These airborne bacteria can come from any number of naturally occurring sources and the
condition can be further aggravated if customers remove the chlorine from their water by way of
an activated carbon filter. Serratia can also grow in tap water in locations such as toilets in guest
bathrooms where the water is left standing long enough for the chlorine residual disinfectant to
dissipate. Serratia will not survive in chlorinated drinking water.
Serratia marcescens is not known to cause any waterborne diseases. Members of the Serratia
genus were once known as harmless organisms that produced a characteristic red pigment. More
recently, Serratia marcescens has been found to be pathogenic to some people, having been
identified as a cause of urinary tract infections, wound infections, and pneumonia in hospital
Once established, the organism usually cannot be eliminated entirely. However, periodic and
thorough cleaning of the surfaces where the pink slime occurs, followed by disinfection with
chlorine bleach appear to be the best way to control it.
To clean pet water dishes, bathroom and kitchen surfaces:
- Scrub the surfaces where phosphorous and fatty substances or the bacteria accumulate with a
brush and a household cleanser.
- Then disinfect the surfaces where the slime has formed with a strong chlorine bleach solution.
Leave the disinfectant solution on the affected surface(s) for 10-20 minutes before thoroughly rinsing away with clean water.
- Use care with abrasives to avoid scratching the fixtures, which will make them even more
susceptible to the bacteria.
To control pink “stuff” in toilets:
- Clean the bowl thoroughly and spray chlorine bleach into the bowl and under the bowl rim.
- Also add 1/4 cup of bleach to the toilet tank.
- Let the bleach stand for 15-20 minutes.
- After 15-20 minutes, flush the toilet a couple of times to rinse the disinfectant out of the tank
and the bowl.
- The bleach should not be left in the toilet tank for prolonged periods; it will damage the rubber valves and seals inside.
- Whenever a pink film starts to reappear, repeat the cleaning and disinfection process.