What kinds of bacteria are commonly found in coffee makers?
Can any be potentially harmful?
Does the bacteria die in the coffee pot because of the high temperature?
Does cleaning the coffee maker and all components reduce the bacteria (a vinegar solution is used?)
Please prove my husband wrong. 
Sites You May Find Helpful
- Kitchen Coffee Maker | Tea Can
- Green Cleaning Solutions – Vinegar – The Bella Life
- Cuisinart DGB-625BC Grind-and-Brew 12-Cup Automatic Coffeemaker, Brushed Metal | Single Cup Coffee Maker
Once, I repaired a coffee maker and discovered a green slime coating the tube between the reservoir and the hot plate. It changed my view of coffee makers.
Essentially, what you’re dealing with is any form of biofilm-producing bacteria. These organisms are generally going to be the same sort that would grow in your tap, if not for chlorination. The predominant species is usually a pseudomonad, a gram-negative rod. This species is typically what gives a biofilm a green slimy look. Micrococcus can be present, also. If your shower tends to get a pasty pink color to it between scrubbing, that’s micrococcus.
Now, as for any of them being harmful, while there is the chance of Pseudomonas aeruginosa and legionella, which both grow in standing water, they’re only respiratory pathogens, and they would die in the heating of your coffee. Even though I say this, I still prefer to use a french press, a percolator or a Moka Express (I have one of each), because all of these devices heat every surface that comes into contact with water. As a result, they cannot form a biofilm, and bacteria will not grow in them.
As for the standard coffee maker, you can try to brew a cup of water, without a filter, and see what comes out. Occasionally, chunks of biofilm do break loose and end up in the grounds. It is my understanding that vinegar (acetic acid) is an effective agent against biofilm, but I’m not 100% positive. I’ve never tried it.
Now, what I’d really rather mention is not bacteria, but fungi. The acidity of coffee is actually not conducive to bacterial growth. Generally, wherever you see a fungus, you have conditions that are mainly unfavorable to bacteria. Bacteria and fungi are mortal enemies, but fungi are slower. If you left a pot of coffee out for a day, it would not have much growing in it yet. The bacteria (almost) never set in, and the fungi take two or three days to take hold. I say this, because if you leave the used damp grounds in the coffee maker too long, then you will get a mold, which means that you could expose yourselves to their spores, a respiratory irritant.