[Jimbee (OP)]

I know growing up I was told never eat food that touched the floor, or food that had been in someone else's mouth. The five-second rule says that food is safe before five seconds elapse. (I was just reading online that most scientists doubt that, at least as a universal rule.) Also around 1993 (especially with a Seinfeld episode), people were talking about the danger of double dipping, or dipping your chip into a dip at a party after you take a bite out of it. (I still think double dipping is disgusting by the way. And I won't eat food that someone did something like that to. Because I've seen people put food from a buffet onto their dirty plate, I've seen use the dirty knife they were eating with to cut food at a buffet. I even saw a man once clean his knife in his mouth before he took food.)

But what surfaces are definitely more dangerous? I was always taught anything that has dirt or dust on it, like the floor. Or a floor if it isn't cleaned often. Plus things like moisture and old food make the situation worse, I think. And also I was brought up to believe that anytime something has dirt or soil on it is visible. That is why when you wash glasses and plates in the sink, you make sure you remove all the visible dirt. (Because you realize there will always be some particles of food on it that are too small to be seen.) Also, I think when you prepare food for a group it is always more dangerous than if you just make food for yourself. And you should always wash your hands before then if you touch your face, cough or sneeze, or use the restroom. Even if you just go number one for that last one. Is all of that true?

So. Which of the above is pretty harmless, which is risky and which should you never do?

[alancalverd]

Never kiss anyone. Never stand in the same room as anyone else. Avoid the company of republicans.

[paul cotter]

I would say the handle of the restroom(as you call it-we call it a toilet) judging by the number of people I see doing their business and exiting without even a basic hand wash.

[evan_au]

The five-second rule

I heard an interview with a scientist who studied the 5-second rule, and found that it wasn't a hard limit (or even a fuzzy boundary). IIRC:
- They tried various drop times between "as little as possible" (< 1 second), 5 seconds, 1 minute and 20 minutes.
- They found some bacteria transfer even in the shortest category
- They found that any coating on the bread increased the transfer
- The worst was moisture-containing coatings like jam/jelly, as bacteria are attracted to moisture

https://www.bbc.co.uk/programmes/m0023whx   (29 minutes)

[evan_au]

When you can't keep food sterile, a traditional solution was fermentation.
- To discourage dangerous pathogens, inoculate the food with a known good microbe
- The good microbes (bred to live in this manner) outcompete many hostile microbes

Examples include:
- Cheese, yoghurt
- Beer, bread, wine, ginger beer
- Sauerkraut, kimchi
- chocolate, miso
- Worcestershire sauce, vinegar, fish sauce, soy sauce

https://en.wikipedia.org/wiki/List_of_fermented_foods

[evan_au]

Don't drink the water in countries that don't adequately sterilize and separate their water and sewage flows.

[paul cotter]

Fermentation can help, it can also go wrong. There is a fermented Chinese product(cabbage?) that is known to contain a carcinogen and the potentially deadly tempe bongkrek where pseudomonas cocovenenans overtakes the fungus and produces several toxins.

[Bored chemist]

Fermentation can help, it can also go wrong. There is a fermented Chinese product(cabbage?) that is known to contain a carcinogen

Alcohol is a carcinogen. :-)

Q What Are The Surfaces That Tend To Be Covered With Dangerous Germs?
A Mucous membranes of humans.

[paul cotter]

That depends on which end you are looking at. I don't think you will find much in the line of hazardous bacteria in the mouth other than those that cause dental caries and the vagina also would be similar. Rectal mucosa on the other hand could easily have clostridia present.

[Bored chemist]

Even a mortuary slab isn't usually "Covered With Dangerous Germs"; nowhere is.

But one precondition of " Dangerous Germs" is that they thrive in/ on humans.
So humans are a good place to look for them.

The bulk of a human is inside the skin, protected by an immune system and thus relatively free of bugs.
The skin itself is generally too dry for most microbes (and it's covered by an army of mostly harmless bacteria).

That leaves the wet bits that are topologically outside the body as the best place to look for harmful bacteria.

Just because the immune system is usually winning the battle doesn't mean the bugs are not there.

And, for what it's wort, I understand there's  usually a greater variety of bacteria in the mouth than the rectum.
As you  point out "Rectal mucosa on the other hand could easily have clostridia present."

How did they get there?

[paul cotter]

Not quite sure, BC, but I will hazard a guess. Clostridia of various pathogenic potential including the tetanus agent are normal commensals in horse intestine but not in humans. Clostridia are spore forming bacteria and these spores are highly resistant to unfavourable environments that would kill most regular bacteria and are capable of waiting prolonged periods until suitable conditions arrive to "despore" and become regular bacteria again. I would guess spore contamination of meat leads to these organism inhabiting the human gut. Take with a pinch of salt, I did three years chem/biochem/microbiology but got bored and never finished.

[Bored chemist]

I'm sure it's something like that.
And that tells us that at some stage those clostridia were found in the mouth.

Given that horses can get tetanus, I'm not sure it's a commensal.

One of  those bugs is useful in another context.
https://en.wikipedia.org/wiki/Acetone%E2%80%93butanol%E2%80%93ethanol_fermentation

[paul cotter]

Tetanus toxin production requires strict anaerobic conditions such as what occurs in a deep wound. Clostridium tetani in a horses gut or a human gut will not cause a problem as the conditions there are not sufficiently anaerobic. Clostridium difficile is a different matter and will cause chaos in one's gut.

[Wellwisher]

One type of surface that is not covered in germs are copper surfaces.

Copper and copper alloys exhibit strong antimicrobial properties, effectively killing bacteria on contact and reducing microbial contamination. These properties stem from the release of copper ions, which disrupt bacterial cell membranes and inhibit their ability to multiply. The U.S. Environmental Protection Agency (EPA) has approved copper alloys as the only hard surface material that can kill over 99.9% of certain disease-causing bacteria within two hours of contact.

Copper door knobs and handles are common in hospitals, being both attractive and self sterilizing.