I roasted a chicken then took the meat off the bone and froze it in little freezer bags. Yesterday evening I thawed some of the chicken in the microwave, expecting to eat it straight away, but didn't eat all of it. I put the leftover chicken in the fridge yesterday evening, after it cooled. Do you think it is ok to eat today? And if so, would I need to heat it up before eating it, or could I eat it straight from the fridge? Thank you!
I certainly wouldn't risk it. The conventional wisdom with things like frozen cooked foods is to eat them within 24 hours of defrosting. If you defrosted it in the fridge you might have a little leeway (but it would still be a risk) but as you defrosted and reheated it in the microwave the likelihood is that eating will make you ill.
Definitely don't reheat it again, you should only ever reheat things once (though I'm less certain of this as many recipes call for cooking and reheating things a number I'd times) as the various heating and coolings increases the risk of dangerous bacteria growth.
Something that many people aren't aware of is it's not the bacteria or fungi (mold) themselves that cause food poisoning but the toxins made by the microorganisms. Of course, if you eat something that's contaminated with bacteria or fungi that can multiply and grow inside our bodies, it will make us sick. But the real danger is the by-products made by these microorganisms - endo and exotoxins from bacteria and mycotoxins from fungi.
Some (many?) of these toxins will be destroyed by heat; still how many of us want to reheat our food to the high temperatures needed for that long? It might now be safe to eat but how good would it taste? An example is the 10 minutes of boiling temperatures for foods such as home canned beans to sufficiently break down the toxin made by Clostridium botulinum.
Not all toxins are destroyed this way either. Reheating might kill the pathogens but you could still be affected by their toxins. So even after killing all possible harmful microorganisms, a person can still get ill. You might be fine eating it but why take a chance?