University of Colorado-Boulder Study Finds Some Showers Deliver a Blast of Pathogens

Research led by Dr. Norman Pace, a Distinguished Professor in the Department of Molecular, Cellular and Developmental Biology at the University of Colorado at Boulder, indicates that showerheads are home to a soupy mix (also called a “bio-film”) of pathogenic bacteria. In their study, the scientists analyzed the bacterial content of 50 showerheads located in apartment buildings, homes, and public places. The research was conducted across the United States in nine different cities located in seven different states, including Colorado, North Dakota, Illinois, and New York. In their analysis, the researchers found that 30 percent of the tested showerheads contained a significant quantity of the pathogen Mycobacterium avium, a bacteria implicated in certain types of lung disease.

M. avium subspecies (rod-shaped bacteria stained red). (Photo credit: CDC/ Dr. Edwin P. Ewing, Jr.)

M. avium subspecies (rod-shaped bacteria stained red). (Photo credit: CDC/ Dr. Edwin P. Ewing, Jr.)

To determine the identities of bacteria living in the showerheads, the scientists collected bacterial samples, isolated DNA from the samples, and used the polymerase chain reaction (PCR) method to identify bacterial species. In addition, the scientists took apart some of the showerheads and used a scanning electron microscope to analyze the showerhead’s surface in detail.

According to the researchers, the presence of M. avium and other pathogens in shower water should not be a major cause for concern for most people. Only those with compromised immune systems, such as the elderly, pregnant women, or those with chronic diseases, are particularly vulnerable to M. avium. Common symptoms related to an M. avium infection include shortness of breath, weakness, tiredness, and a dry cough that does not go away.

However, the scientists did provide two suggestions as to how to decrease your exposure to pathogens that may live in your showerhead. First, they suggest allowing the water to run for a few seconds before entering the shower, as the first blast of water from the showerhead typically contains the most pathogens. Also, the scientists suggest switching from a plastic showerhead to a metal showerhead, as they found that metal showerheads commonly harbor fewer bacteria than those made of plastic.

The results of the scientists’ research was published online in the September 14, 2009 edition of the journal Proceedings of the National Academy of Sciences. In addition to Dr. Pace, other researchers who contributed to the study included Leah Feazel, Laura Baumgartner, and Kristin Peterson of CU-Boulder and Kirk Harris of the University of Colorado at Denver.

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The Spoils of War — How T Cells Refuel to Wage War on Pathogens

A killer T cell attacks an infected cell.

In humans, T cells fight viruses and other invaders. Scientists have long thought T cells simply killed an enemy and then moved on to fight others, but new research suggests that some T cells use the spoils of their battles to win the larger war.

White blood cells are part of the immune system, the human body’s main defense against viruses and other infectious agents, all of which are called pathogens. Pathogens take over the machinery of a cell and cause it to manufacture more pathogens, leading to infection. The body has six major classes of white blood cells, each offering specific weaponry and tactics for combating infection. One class of white blood cells is the lymphocytes, which include T cells and B cells.

Killer T Cells

One type of T cell, the CD8+ T cell, is known more commonly as a “killer” T cell. It attacks infected cells with cytoxins, which cause the plasma membrane of an infected cell to open, allowing water, ions, and toxins to rush in. The infected cell then swells and bursts, destroying the pathogens that have taken over the cell. Until recently, scientists thought that T cells left their victims after killing them and simply moved on to attack other infected cells. Results of recent research, however, show that the interaction between killer T cells and infected cells is more like that of predator and prey.

Caught “Green-Handed”

Mark Slifka and Carol Beadling, researchers at Oregon Health & Science University’s Vaccine and Gene Therapy Institute, happened upon this discovery while observing interactions between killer T cells and cells infected by a virus.

Slifka and Beadling dyed infected cells with a fluorescent green dye so that these cells could be more easily seen under a microscope. They then unleashed killer T cells that were specific to the virus of the infected cells, to observe their interactions. They watched the small T cells attack and kill the large green infected cells as expected. But Slifka and Beadling noticed something strange. The T cells, which had not been dyed, were themselves turning green as the infected cells broke apart. Slifka and Beadling realized that the T cells were actually eating portions of the infected cells’ membranes. Like a child whose tongue is stained purple from a popsicle, the fluorescent dye was a telltale sign that the killer T cells weren’t just killing the infected cells, they were feeding on them. They had been caught “green-handed.”

A Well-Fed Army

A fluorescent infected cell is killed and partially devoured by killer T cells. (Credit: David Parker and Scott Wetzel/OHSU)

“This is truly a case of microscopic cannibalism,” Slifka says. “And this is the first time we’ve seen virus-specific killer T-cells ingest parts of infected cells.” Slifka thinks that the benefit of this behavior is that T cells can refuel themselves before fighting other infected cells. He compares this to an army of warriors that invades a city, destroys it, but takes care to gather resources that could help it maintain strength in its ongoing war. “Not only do you have this warrior cell coming in and attacking these virus factories, but it’s able to take away nourishment from this in order to help it to continue the fight against the infection,” he says.

A similar response to virus-infected cells by CD4+ T cells, also known as “helper” T cells, was observed by researcher David Parker, also of the Oregon Health & Science University. The value, Slifka says, of these discoveries about T cells is that the same experimental techniques used to study interactions with pathogens could be applied to observe and measure the response of T cells to a vaccine.

Hope for Vaccines?

A vaccine is a substance that carries the identifying markers, or antigens, of a virus but does not have the destructive capabilities of the actual virus. Some vaccines are made from dead viruses. Others are weakened versions of a virus. A vaccine triggers an immune response. The body produces lymphocytes such as B and T cells that will be able to recognize the real virus should it ever appear in the body. In other words, a vaccine teaches the human body how to identify and defeat a virus, but without putting the body through the danger of the real viral infection.

Slifka’s findings suggest that if a vaccine were marked with a fluorescent green dye, and killer T cells were then unleashed to attack and consume the vaccine, scientists could accurately measure the interaction between the vaccine and the killer T cells. This could help determine a vaccine’s effectiveness, as well as the dosage needed to immunize a person.

More to Explore

Check out the following sites to hear from Dr. Slifka, read more about his discovery, and watch killer T cells as they kill and eat an infected cell.