With BART currently deciding what kind of seats to put in its new fleet of cars and commuters' continual disgust with the existing blue fabric seats, we decided to test the BART seats to see what germs are lurking in the cloth.
You can read our full story about what we found, the implications for BART and riders’ reactions here. Below is a behind-the-scenes look at the science in the story.
BART Seat Science 101
After we inquired at the San Francisco State University science department, Darleen Franklin, a supervisor at the biology lab who’d conducted similar tests in the past, volunteered to help us. Our object was to find out what was growing in BART seats. We also decided to test a plastic Muni seat for comparison, since BART is now choosing between plastic, vinyl and cloth seats for its new cars.
We set out in the mid-afternoon on Feb. 2 and jumped on the 28, a Muni line that runs from San Francisco State University to the Daly City BART station. It’s a line that’s used heavily by college students who some might consider not the most cleanly creatures in the world.
We swabbed a back seat in the bus, then cleaned it with an alcohol wipe and swabbed it again, with the idea that we would find out how easy it was to clean the plastic. The college students were listening to their iPods, texting on their phones, and no one paid any attention to us.
At the Daly City BART station, we hopped on a train headed for Dublin/Pleasanton to collect our BART samples. Again, we went to the back seat, where we swabbed the headrest and the seat cushion before and after cleaning the seat with an alcohol wipe. We also found a stray thread that we took to the lab to test. Lastly, we tested the air to provide a baseline.
Back at the lab, Franklin took all the swabs and streaked them onto petri dishes. Then we waited. On Feb. 16, I went back to see what had grown. You can see the results in the pictures.
The sample from the plastic Muni seat produced two small colonies of bacteria. The sample taken from the Muni seat (top row) after it had been cleaned with an alcohol wipe showed no bacteria growth at all. Franklin said that indicated that the Muni seat was easy to disinfect.
Next, we looked at the sample from the headrest of the BART seat (second row). Both bacteria and mold were growing. The alcohol wipe worked on the headrest, as no bacteria were detected after it was cleaned.
The sample from the BART seat cushion (third row) was quite a sight. There was an explosion of fluorescent bacteria colonies — at least nine different strains — as well as mold. Even after the seat cushion was cleaned, bacteria still grew. The thread that we took also produced several colonies of bacteria.
The next step was to do tests to identify what kind of bacteria we had found.
Finally, Franklin tested the bacteria strains to see if they were resistant to antibiotics, a sign that they would be potentially harmful to BART riders. The way she tested for drug-resistance was to grow the bacteria on a sheep-blood plate that had little discs of antibiotics on the surface (see row four). If the bacteria avoided the discs, then we knew they could be killed with an antibiotic; if they did not, we would know that they were resistant to the drugs.
Franklin identified three strains of bacteria — all from the BART cushion — that were resistant to antibiotics.
One strain was resistant to tetracycline and a sulphur-based antibiotic. Other tests showed that that bacteria likely came from “fecal contamination,” as Franklin put it. That is, someone either failed to wash their hands after using the bathroom or just messed themselves on the BART seat. Another strain that was resistant to penicillin was from the same source: the human gut.
The last strain of bacteria that was resistant to antibiotics was particularly concerning. In two separate tests, Franklin identified characteristics of methicillin-resistant staphylococcus aureus, or MRSA, growing in the seat. The first test (middle of row four) confirmed the presence of staphylococcus aureus, the skin-borne bacteria, because the bacteria turned the mannitol salt agar plate yellow from red. A second test confirmed that the bacteria was resistant to the antibiotics methicillin and penicillin, like MRSA (the last picture in the fourth row). The bacterial growth was unaffected by those two antibiotics, growing right through them.
However, a third test to see if the bacteria would devour sheep blood cells, something that MRSA normally does, came back negative. Franklin said this meant that the bacteria had characteristics of MRSA and could be MRSA, but more tests would be needed to confirm exactly what it was.
MRSA is known as the “superbug” because it is resistant to antibiotics. It infects people through open wounds, attacking the immune system; 19,000 deaths each year are related to MRSA infections, according to the Centers for Disease Control and Prevention.
Both cloth and hard plastic seats are exposed to bacteria and dampness from riders. As we reported, 330,000 commuters ride BART each day. Last year, BART police received 1,051 complaints of smoking, eating and drinking; 245 complaints of urinating or defecating; 82 reports of indecent exposure, including masturbation; and 56 reports of spitting.
Our experiments indicate that Muni seats are more sanitary and easier to disinfect. BART seats, in contrast, are a breeding ground for mold and bacteria. They are much more difficult to disinfect and dry off, and therefore microbes thrive in the cloth.
Web production by Tasneem Raja.