Season 3, Episode 7: One Hand Washes the Other

Joanna dies from a C. difficile infection while in quarantine in Racine, Wisconsin. David and Carlos travel to Ojai, California to chase down the bacteria source at a plant nursery. David finds C. difficile in a pit toilet used by migrant workers—it turns out the bacteria-laden waste has been leeching into the water supply used to irrigate the nursery plants. After some molecular testing, the NorBAC team realizes that the bacteria in the pit toilet don’t carry the same antibiotic resistance genes as the strain that killed Joanna.

Image provided courtesy of Shaftesbury Films.		Carlos and Elvia collect a soil sample at the contaminated farm.

IS IT POSSIBLE TO CATCH A FATAL DISEASE BY BEING NEAR PLANTS?

What is C. difficile?

Clostridium difficile is a type of rod-shaped bacterium that is found almost everywhere including in soil and the human gut. First discovered in 1935, C. difficile is resistant to most antibiotic drugs, which makes it difficult to kill. There are, however, anti-clostridia drugs designed specifically to fight infections of Clostridium-family bacteria.

Image provided courtesy of AXS Studio Inc and Shaftesbury Films.		Artist’s rendition of a magnified view of C. difficile.

The C. difficile that lives in our intestines generally makes up a small portion of the total bacteria found there and normally does not cause disease. But, people in long-term health care or on certain antibiotics can carry higher than normal numbers of intestinal C. difficile , which can lead to a condition called pseudomembranous colitis, a serious colon infection.

How is C. difficile transmitted and how deadly is it?

C. difficile is passed by fecal-to-oral transmission. Some infected individuals may show no symptoms, while for others the infection may be life threatening. Pseudomembranous colitis symptoms include diarrhea, fever, and abdominal pain. If not treated early and aggressively with anti-clostridium drugs it can cause a very serious condition called “toxic megacolon,” or even death.

Recently, there have been several notable outbreaks of C. difficile : In Canada in 2003-04, about 1,400 cases in total occurred in Montréal, Québec and Calgary, Alberta, and in 2005 the outbreak spread to Toronto, Ontario. In 2005, researchers at McGill University in Montréal, in collaboration with Génome Québec's research facility, announced they had cracked the genetic code of the highly virulent Québec strain of C. difficile . It is expected that this will allow quicker detection of infection and better treatment.

So...

Yes, it is possible to die from C. difficile infection and yes, because the bacteria live in soil, it is possible to catch C. difficile (if you don’t already have some in your gut) from handling contaminated soil and then transferring the bacteria from your unwashed hands to your mouth – while eating, for example – or from drinking water contaminated by soil run-off.

IS IT POSSIBLE FOR LIGHTNING TO CAUSE TWO DIFFERENT BACTERIA TO TRANSFER THEIR GENES TO EACH OTHER?

Image provided courtesy of AXS Studio Inc and Shaftesbury Films.		Lightning strikes bacteria in the soil, causing the release of plasmid DNA.

What is bacterial conjugation?

Bacterial conjugation is the transfer of genetic material from one bacterium to another. Not all bacteria can initiate conjugation. Conjugation is initiated by a bacterium that contains a specific segment of DNA called an F plasmid. That bacterium builds a little bridge that connects to a neighboring bacterium. Once they’re connected, the initiating bacterium copies that F plasmid and the new copy crosses the bridge and enters the second bacterium. The conjugated bacteria then separate, with both now able to initiate conjugation with other bacteria.

F plasmids may contain a number of genes, including those that enable bacteria to initiate conjugation as well as antibiotic resistance genes, which help bacteria survive.

What is electroporation?

Electroporation is a technique that uses electricity to briefly cause holes to form in the outer membrane of cells. The temporary openings in the cells’ outer layers can allow entry of any small segments of genetic material floating outside and near the cells. Electroporation works within a narrow voltage range (generally 12,000 to 19,000 volts): lower voltages do not open up the membrane and higher voltages can kill a cell.

Molecular biologists use electroporation as a tool to get recombinant DNA, molecular probes or other small molecules – like some drugs – into cells.

So...

It’s probably not possible for lightning to cause bacteria to swap genes, although there are other ways, like bacterial conjugation, that allow bacteria to transfer and “share” genes. In the case of electroporation, it’s possible to use a controlled amount of electricity to get bacteria to take up small pieces of genetic material. But lightning strikes can be powerful – up to three million volts, which could kill a person not to mention single-celled bacteria.

- by Audrey M. Huang, Ph.D.

Want to read and learn more?

To learn more about bacterial conjugation, visit:
www.hhmi.org/biointeractive/animations/conjugation/conj_frames.htm

To learn more about electroporation, visit:
http://en.wikipedia.org/wiki/Electroporation