Legionnaire’s disease is a severe type of infection caused by an aquatic organism that increases in warm environment known as Legionella pnuemophila. As such, this infection produces the disease called pneumonia. Legionnaire’s disease obtained its name during an outbreak of pneumonia in 1976, when the bacteria infected the participants of the American Legion convention in Philadelphia.

Recently, researchers at the Yale School of Medicine have reported that the proteins within the said bacteria ensure their survival. Such proteins work by trapping and carrying such bacteria safely to live and infect healthy cells.

In studying bacteria, a simple instrument that can assist a researcher is the brightfield light microscope. A brightfield light microscope illuminates the specimen sample through transmitted white light, like the illumination that originates from below and observed from above. Aside from the built-in illuminator, a good brightfield light microscope is equipped with an adjustable condenser that has an aperture diaphragm or contrast control. Aside from those, other parts of the brightfield light microscope are the mechanical stage and the binocular eyepiece tube. Some of the significant advantages of using a brightfield light microscope are the simplicity of the technique and the minimal sample preparation.

According to the lead author of the said report and associate professor of microbial pathogenesis at Yale, Craig Roy, the team of researchers was fascinated by the newfound scheme of these simple organisms because their so-called tricks allowed them to manipulate cells in the human body, which normally should have been functioning as protection against infections.

The bacteria that cause the said disease reproduce inside the macrophage. Macrophages are cells that are part of the body’s immune system. These protective cells eat debris of cells and toxins. Macrophages also kill bacteria by carrying them in storage bubbles, known as vacuoles, to organelles. Organelles contain enzymes that are responsible for breaking down the intruders.

Roy further stated that the uniqueness of this pathogen lie on its ability to direct the vacuole produced after the macrophages swallows the bacterium. By maneuvering the vacuole towards the endoplasmic reticulum, the bacteria then thrive because the said organelle is rich in nutrients.

This Yale group of researchers was able to identify the Legionella proteins that are responsible for the high jacking of the vacuole. One of their discovered proteins, DrrA, is accountable for turning on the molecular switch called, Rab1, and then sabotages its function. As such, the Legionella is able to fuse the endoplasmic reticulum and the transported vacuole. This results to the creation of a compartment that ensures the survival of the bacteria. Another protein that the researchers discovered is the LepB. Such protein is responsible for turning off the RaB1 switch once the Legionella has successfully entered the nutrient-rich organelle.

To simplify the process, Roy made the illustration with the Legionella as a crafty burglar that stealthily enters a cell and exploits the protein, DrrA, to turn on a light switch, Rab1. As such, the location of the safe, which is the endoplasmic reticulum, illuminates. Once Legionella has cracked the safe open, protein LepB turns the light off to avoid detection.