ucsdhealthsciences: Bologna dropped on a kitchen floor can bear an unsettling resemblance to Petri d

ucsdhealthsciences: Bologna dropped on a kitchen floor can bear an unsettling resemblance to Petri dishes containing Salmonella bacteria. Eat. Think. And be wary. Most folks know the “five-second rule,” an unwritten convention that says if you drop a food item on the floor it may be picked up, dusted off and safely consumed within that designated amount of time. Apparently this assumes microbes need at least six seconds to make the jump. In recent years, the scientific integrity of the five-second rule has come under occasional empirical scrutiny. In 2003, for example, a team of scientists at the University of Illinois at Urbana-Champaign, led by a high school senior Jillian Clarke on a six-week summer internship, investigated the phenomenon. Initially stumped by a lack of working bacteria (they could find no floors on campus with sufficient quantities of indigenous pathogens), the researchers resorted to a controlled experiment in which they coated tiles with a broth of Escherichia coli, a generally harmless intestinal bacteria with the exception of a few strains like E. coli O157:H7 that can cause severe abdominal cramps, diarrhea and vomiting. Clarke and colleagues then dropped Gummy Bears and Fudge Striped cookies on them for specified amounts of time. They found that large numbers of bacteria did in fact transfer to the fallen food within the five-second limit, but given their earlier, futile efforts to find floors sufficiently rife with pathogens, they concluded that the five-second rule was not incontrovertibly repudiated. This was a good thing given some of their ancillary findings. In an accompanying survey, Clarke reported that 56 percent of males admitted to invoking the five-second rule, and a whopping 70 percent of females. (It was not determined what percentage of food dropped by women was then given to men.) All of the respondents acknowledged that they were more likely to invoke the five second rule for a piece of candy than for a dropped vegetable. For her efforts, Clarke was awarded the 2004 Ig Nobel Prize in public health by the Annals of Improbable Research. Clarke’s ground-breaking research was followed up in 2007 by a pair of science majors at Connecticut College who swiped apple slices and Skittles across the floors of the college dining hall and snack bar for predetermined intervals of five, 10, 30 and 60 seconds. They found, oddly enough, that bacteria didn’t transfer in measurable numbers to apples until almost a minute had elapsed. It took microbes almost five minutes to climb aboard Skittles. But the Connecticut College findings were almost immediately rebuffed by a 2007 Clemson University study by food scientist Paul Dawson and colleagues in which slices of bread and bologna were exposed to various sample surfaces – wood, tile, nylon carpet – coated with Salmonella, a major source of foodborne illness. Contrary to all earlier findings, Dawson’s team found that pathogenic Salmonella not only have no problem contaminating dropped food, they do it very quickly. Within five seconds, both meat and bread had picked up 150 to 8,000 bacteria. After a minute, the numbers were increased tenfold. Tile and carpet transferred the most microbes. According to experts, it takes fewer than 100 E. coli or 10 Salmonella bacteria to constitute an infectious dose. A later report out of Manchester Metropolitan University found that dropped foods with higher moisture content more easily assumed microbial pathogens than drier comestibles. Sugary foods attracted (and promoted) microbes more than salty foods. So does the five-second rule have any validity? Well, given the ubiquity of bacteria in and around us (an estimated 100 billion in your mouth at any moment; 7 billion on a kitchen sponge), there’s some argument to be made that we have evolved sufficient immune defenses to tolerate a microbial dollop to fallen food. On the other hand, a 2008 University of Arizona study found that 93 percent of examined shoe bottoms bore traces of fecal bacteria. It may not be a case of worrying about where dropped food has been but rather what’s been walking (and now residing) on that floor.  -- source link

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