What are really really bad molds?

In fact, there is no such a standard in CDC or NIH, or even the medical societies, who has or have set a criterion. But medical and clinical research already had found many commonly isolated molds or fungi from animals and human. Every medical text book has those mold or yeast names described. Since people are getting older and living longer, new fungal pathogens are growing and emerging.

All molds and yeasts are bad!!!

The book "Atlas of Clinical Fungi. G. S. de Hoog et al. 2000. CBS Netherlands" described thousands of fungal molds and yeasts, which are reportedly isolated from animal or human hosts published in scientific journals.

Medical mycology textbooks mainly include those common but pathogenic molds and yeasts:

Aspergillus fumigatus; Coccidioides immitis; Paracoccidioides braziliensis; Histoplasma capsulatum; Blastomyces dermatitidis; yeast Candida albicans; yeast Cryptococcus neoformans; Dermatophytes, which infect skin and nails.

  • Any molds that can grow in 37C are potentially human pathogens.
Because within human body, the temperature is 37C, a mold to be a pathogen, has two conditions to meet: to tolerate a 37C temperature and to resist or evade the human immune system.

  • All BSL-3 and some BSL-2 molds!
BSL-3 molds: such as Penicillium marneffei; Coccidioides immitis; Histoplasma capsulatum.

BSL-2 molds: such as Aspergillus fumigatus; Aspergillus flavus; Aspergillus terreus.

  • Opportunistic yeast pathogens: Candida albicans and Cryptococcus neoformans
Both yeasts are saprobes, yet they are capable of invading humans if the host has weakened immune systems. Candida can even invade human skin, digestive tract and reproductive tract, causing so-called "Candidiasis". Cyrptococcus can cause "Cryptococcosis".

  • Dimorphic fungi
Dimorphic fungi are meant that a fungus can take both morphological forms: in filamentous moldy form or a more-or-less yeast form, upon different culture conditions. Most fungal pathogens do take yeast forms once they are invaded human tissues.

Courtesy of Nature Review Immunology, by Luigina Romani, @ http://www.nature.com/nri/journal/v4/n1/box/nri1255_BX2.html