Pseudomonas

by Gaddy Bergmann

If there is a cockroach of the microbial world, it is Pseudomonas.  Their cells are shaped like tiny rods, and have whip-like tails called flagella that let them swim over everything. Pseudomonas need very little food or water to survive, and are found all over the world. They live in soil and water, and on plants and animals. One monkish species of Pseudomonas can even grow in distilled water. What could they possibly be eating in such clean water? Well, even though distilled water is very clean, Pseudomonas can still find something to eat and survive. They thrive by living where few other bacteria can.

Another Pseudomonas species can cause disease in plants by taking away their food. It starts by forming ice on the leaves and stem and causing frost damage. Once the skin is broken, the bacteria go inside and cause disease. A third  “famous” species (fame is oh so relative) of Pseudomonas has been genetically modified to allow it to eat oil spills! Pseudomonas can also sense chemicals from other Pseudomonas. When the chemicals become concentrated, the bacteria notice this and change their behavior. So, they may swim together or apart, or they may stop making one chemical or start making another. Even on chair you are sitting on right now, they are sensing each other, measuring the crowded world.

Sometimes Pseudomonas is blue or green, making it look like algae, even though it is a bacterium. Those colors come from useful pigments that can soak up iron to be used as food, or to poison other bacteria. Unfortunately, these same pigments also sometimes cause disease in people and animals. Pseudomonas is not one of the most dangerous bacteria to people, but it can cause disease in a wound that is already open, or in those who are already sick. It makes us sick in the same way it makes a living: by persisting.

Diseases caused by bacteria are called infections, and they are often treated with antibiotics. These medicines are usually good at killing bacteria, but not always.  This is because some bacteria possess or evolve resistance to them. Bacteria that are resistant to a certain antibiotic are not killed by it. Pseudomonas is resistant to several different antibiotics; a resistance that has evolved because of the overuse and improper use of antibiotics. So, if a patient has a Pseudomonas infection, then the doctor has to use one of the antibiotics that still  work on Pseudomonas, and hope that Pseudomonas does not evolve resistance to that antibiotic too. Sometimes people check into hospitals for one illness, but contract Pseudomonas or other bacteria while they are there. When Pseudomonas lives inside breathing machines, patients may accidentally inhale them and develop a lung infection (pneumonia). One of the ways Pseudomonas prevents itself from being killed by other bacteria, human immune systems or antibiotics is by covering itself with a slime. In preserving itself in this way, Psuedomonas may cause harm to others. To get past this defense, doctors may increase how much antibiotic they give to their patients, though these increased dosages will ultimately favor Pseudomonas with new tricks to survive.

Pseudomonas is one of nature’s toughest survivors. It can live in many different environments, from soil to water to our own bodies. It does not need much food, and it competes well against other microbes. It does not cause disease often, but when it does it can become quite dangerous. Pseudomonas is resistant to some antibiotics, but luckily we have others to use against it. We could begrudge Pseudomonas for its indiscretions, but we might also look to it for models of success; it, after all, has a far longer history than humanity of getting by.

About the Author

Gaddy Bergmann is a doctoral student in microbial ecology in the laboratory of Noah Fierer at the University of Colorado Boulder. He uses DNA sequencing to identify plant and bacterial species in bison dung, in order to assess how microbial communities may respond to changes in diet. Prior to his work at Colorado, Gaddy was a research associate in clinical microbiology at a biotech company and a science teacher. He has published scientific articles on microbial and fish ecology, as well as a science fiction trilogy called The Feral World. Gaddy was born in Petah-Tikva, Israel, and grew up in Denver, Colorado.