Why stinky old bacteria generally don’t smell.
In 2001 New Scientist reported that the US Army was hard at work building the “mother of all stink bombs.”
As part of its Non-Lethal Weapons Program, researchers were apparently hunting for an odor so odious that it would trigger an overwhelming urge to run away, as a way of dispersing hostile crowds or enemy troops.
The New Scientist article also mentioned a remarkable product known as “US Government Bathroom Malodor,” an abominable mixture brewed up to test the efficiency of deodorant cleaning materials.
It was a kind of Standard American Stink, which by all accounts smelled like, uh, poop—only “much, much stronger.”
Although the ingredients of the Army’s stink bomb were classified, they were probably mainly chemical in nature.
However bacteria have a pretty bad reputation in the odor department.
In fact, a Google search for “stinky bacteria” returns over half a million results.
Before we get into the whys and wherefores, however, we ought to begin by showing due gratitude that the presence of certain types of bacteria can in certain circumstances produce a particularly putrid pong, and that’s when food goes “off.”
Not everyone abides by sell-by dates, with more than a few brave souls applying a “smell test” to decide if it’s safe to eat something.
Now, while this isn’t always sensible (not all bad bacteria are stinky) it’s possibly one of the factors that kept our prehistoric ancestors alive.
There probably weren’t many sell-by dates on food in the Serengeti, so Neanderthal humans would very likely have stuck to items that smelled OK.
Those that didn’t take this precaution may have met an untimely end, meaning they didn’t get a chance to pass on their genes, and also meaning you and I have inherited a genetic propensity to avoid bad-smelling food.
Actually, although many believe that bacteria themselves are smelly, they’re almost certainly not—what happens is that when bacteria metabolise other substances, they produce end- or by-products that are often volatile, and sometimes have distinctive odors.
After vigorous exercise, you may blame sweat for the smell, but it’s really not the sweat’s fault.
The odor is, instead, produced by bacteria metabolising your perspiration, then in turn producing the whiffy by-product.
Many bacteria are fond of sugars, producing different odors as they digest them.
The distinctive smell of foot odor is often caused by Bacillus subtilis and Staphylococcus epidermidis, while funky underarms (sounds a bit like a band) tend to result from Corynebacterium xerosis.
Reportedly, experienced lab technicians develop an ability to identify bacteria from the smells they give off when being cultured.
A fascinating online exchange of techs’ experiences reveals that Pseudomonas aeruginosa has an initial smell of grapes, with a secondary scent of tortillas.
(I’m not making this up.)
Less pleasantly, C. difficile apparently smells like horse manure or elephant dung.
And worst of all, perhaps, E. coli is said to smell somewhere between vomit and melting Styrofoam.
Humans of course might well shy away from a job that involves sniffing horse poop, but fortunately there’s another animal that can’t get enough of it.
Researchers at a teaching hospital in Amsterdam have trained a two-year-old male beagle named Cliff to detect C. difficile in stool samples, or even by simply sniffing hospital patients in their beds.
Cliff correctly identified 25 out of 30 patients who were suffering from a C. diff infection, and only misidentified five patients out of 270 who were uninfected, acting as experimental controls.
When Cliff detects C. diff he’s been trained to sit or lie down.
If you have ten minutes to spare, and enjoy a good dog story (and come on, who doesn’t?) I can thoroughly recommend a video about Cliff, produced by the British Medical Journal.
You’ll find a link below (it’s the third one down).
And finally I feel it’s my duty when talking about how to decide whether something is safe to eat or not, to remind us all of the story about the two cannibals who were sitting down to eat a clown.
One turns to the other and says, “Does this taste funny to you?”