I love the link Josh gives, but have found that so many people are unlikely to create 300 loci in advance.
Plus, you mention that you want to memorize bacteria - how many strains? If that number is 300, there are ways to link material together that would reduce the need for 300 stations. You just wouldn’t necessarily know in advance how many stations you need without some practice.
In my own work, I tend to create either just as many as I need or more. I almost always never wind up using them all.
Perhaps in the future, schools will include mnemonics as a subject and people will have that Memory Palaces sufficient for use ready to go at all times (apparently they’re doing something like this in Mongolia in some parts of their school system).
For myself, I used to memorize material from dense books very strategically.