Leftover Onions Are Poisonous?

There are claims that leftover onions are poisonous because they are "magnets for bacteria." There are also claims that "leaving onions around a room can absorb the flu virus along with bacteria that cause other illnesses thereby preventing people from becoming sick".

So, onions are magnets for bacteria. That doesn't make sense. Magnets? For just bacteria? Just bad bacteria? How does that work? Even if bacteria, just bad bacteria, could somehow travel to an onion, I'd think the sulfur compounds would do them in.

Looks like Dr. Joe Schwarcz of McGill University Office for Science and Society wondered the same thing.¹

"The terminology that onions are "bacterial magnets" makes no sense. No food attracts bacteria, although of course some are more likely to support bacterial multiplication once infected."

And...

"Onions are not especially prone to bacterial contamination. In fact, quite the opposite. Onions feature a variety of sulphur compounds that have antibacterial activity. Furthermore, cutting an onion triggers the release of enzymes that initiate a chemical reaction producing propenesulfenic acid, which in turn decomposes to yield sulphuric acid. It is the sulphuric acid that makes you cry by irritating the eyes! But sulphuric acid also inhibits the growth of bacteria. Also, a cut onion's surface dries out quickly, reducing the moisture that is needed for bacteria to multiply."

He gives these reasons for consuming onions:

"That’s because onions contain a variety of compounds that have health benefits. Fructo-oligosaccharides, for example, stimulate the growth of bifidobacteria which suppress the growth of potentially harmful bacteria in the colon. Eating onions has also been linked with a reduced risk of stomach cancer and flavonoids in onions can lower blood pressure and reduce the risk of blood clots forming. Some studies have even shown improved lung function in asthmatics who consume lots of onions."

This Dr. Joe is an interesting person. I wish he had a blog. ________¹Is It True That Onions Are “Magnets For Bacteria?”
Photo of an onion I had leftover in the refrigerator.