Toxins summary is good and very HY I'd imagine. As well as in the "laboratory microbiology" section there are some very useful/important topics like "dna viruses" and "rna viruses." There are a handful in there that hit the really important stuff to help you master which viruses are enveloped vs naked, ss vs ds, circular vs linear. The growth media is a good one too. I've seen a lot of questions that depend entirely on your knowledge of the name and/or make-up of the media used to culture an organism.
As far as which bacteria/parasites/viruses?
HIV is a MUST. enteroviruses, hep B and C viruses, paramyxoviridae.
Staph, strep, pseudomonas, h. flu, e. coli, salmonella, shigella. Neisserias, chlamydia, treponema. I'd think those are guaranteed subjects on the test for just about everyone.
Candida, aspergillus, histoplasma, blastomyces, cryptococcus, coccidioides. Those to me seem to stand out the most for the fungi.
Not really sure on parasites which ones are the most high yield. I feel like I don't see that many questions for them anyway.
I'm sure others could contribute, but those are the ones I feel like I see the most.