Honey: Bacteria’s Worst Enemy
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Honey: Bacteria’s Worst Enemy

Honey. You’ve met honey. It’s that sticky,
sweet stuff. Basically just slightly liquidy sugar in a
plastic bear bottle, right? Wrong! Honey is a supercharged bacteria-killing
powerhouse. And it’s all down to what those hardworking bees put into it, from immune
proteins to the sugar itself. Since ancient times, honey has been used to
prevent wounds from getting infected. And these days, we use purified and standardized
versions of honey to fight infections in hospitals. Honey has three main tricks for fighting bacteria. The first is all that sugar. Honey is only about 17% water. Most–but not
all–of what remains is sugar. The two main types of sugar in honey are glucose
and fructose. Like all sugars, glucose and fructose are sticky — they attract water. Honey is technically a supersaturated solution,
meaning it contains more sugar than would normally dissolve at that temperature. That’s
why it eventually gets all crystally in the pantry — over time, the sugar comes out of
the solution. Chemically speaking, it’s desperate for
water. Water can travel across cell membranes from
where there’s a higher concentration of water to where there’s a lower concentration.
And there’s a higher concentration of water in a bacterium than in honey. Which means that honey will suck the juices
right out of any bacterium — or mold, or fungus — that tries to set up shop. Plus, there’s isn’t enough water in honey
for any microorganisms to live on. So they die, and the honey doesn’t spoil. The second thing, is that when bees make honey,
they throw in an enzyme called glucose oxidase. And bacteria hate glucose oxidase because
it produces two different compounds. It converts glucose to gluconic acid and hydrogen
peroxide. Gluconic acid is, you guessed it, an acid.
It gives honey a pH value of less than 4. That’s about a thousand times more acidic
than the neutral pH of 7 that most bacteria need to grow. And hydrogen peroxide is very good at killing
cells. It destroys the cell walls of bacteria, which breaks them apart. Glucose oxidase isn’t active in ripe honey–there’s
not enough water for it to work properly. It seems to be there to keep the honey from
spoiling while the bees are drying it out. But if you dilute honey, the glucose oxidase
will switch back on and make gluconic acid again. The final thing bees do to make honey antibacterial?
They put antibiotics in it. Some types of honey contain a protein called
bee defensin-1, which is exactly what it sounds like. Bee defensin-1 defends bees. It’s part of
their immune system and protects them from certain bacteria, including ones that could
cause nasty diseases inside the hive. It’s produced in a gland that bees use to
make honey, so it makes sense that some of it would make it into the finished product.
And while scientists aren’t sure how much of the protein is really in honey, it sort
of makes sense that bees would use it to protect their food. Another antibacterial compound sometimes found
in honey is methylglyoxal. Methylglyoxal is a small organic molecule
that forms in honey from a compound in the nectar of certain flowers. There’s an especially large amount of methylglyoxal
in manuka honey, a honey made from a New Zealand flower. This honey is so good at killing bacteria
that it’s actually used in hospitals. There’s one bacterium that has honey’s
number–but only sort of. It’s the type of bacteria that that causes
botulism. The bacteria start out as spores, which are
very hard to kill. They’re already dried out, so honey’s
water-sucking properties don’t kill them, and because the spores aren’t growing, they
aren’t affected by the acidity or the antibiotic compounds. The really dangerous part of the bacteria
is the botulinum toxin they produce when they grow into mature bacteria. Less than a hundred
nanograms — that’s billionths of a gram — is enough to kill an adult. About 10% of honeys have some botulinum spores
in them. But since the spores in honey aren’t growing and making toxin, they’re harmless
to healthy adults. Our immune systems intercept the spores before they can start growing inside
of us. But the immune systems of infants aren’t
always able to kill those spores before they start growing. So, in rare cases, the bacteria
can germinate and start producing toxin. That’s why it’s not safe to give honey
to infants under one year old, but the rest of us don’t need to worry about it. So the next time you’re looking for something
sweet, go ahead — eat some of bacteria’s worst enemy. Thanks for watching this episode of SciShow,
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