Bold Mold, Beastly Bacteria
and Other Microbial Assassins

Excerpted from a series of articles on unexpected microbial diseases, 1995

PART 1. SHAPE SHIFTERS

People expect the worst from toxin-secreting bacteria like Staphylococcus aureus and Clostridium difficile. But fungi don't have a reputation for nastiness. Most, like Baker's yeast, are reliably benign. Some are downright friendly: an obvious example is Penicillium notatum, which gave us the most powerful weapon we have to fight bacterial infections. Even medically important strains of fungi such as Candida are invariably opportunistic, able to outmaneuver the immune systems of only the most weakened hosts. Their usual victims are patients severely impaired by AIDS, cancer chemotherapy, or drugs used to suppress organ rejection.

That's why the medical community was so startled in the mid-1980's when epidemiologist Richard Wenzel, now at the University of Iowa, announced that fungi --not bacteria-- killed almost 40% of patients who died from the infections they developed while in the hospital. Even more startling news emerged in the 1990s: The Centers for Disease Control and Prevention (CDC) reported that healthy people were falling prey to fungi. And not the organisms Infectious Disease gurus would have predicted. In 1994, for example, Los Angeles residents were infected with an endemic soil fungus, Coccidioides, after tremors from the Northridge earthquake launched their spores into the air.

Coccidioides are shape shifters --they grow as molds in the wild and change into yeast when captured. Molds (or "moulds," the spelling mycologists prefer) are multicellular and slow, growing in lazy, "fuzzy" colonies. In contrast, yeasts are small and fast, traveling as unencumbered single cells. Molds reproduce by forming spores, an arduous process. Yeasts simply bud, pinching off portions of themselves to replicate on the run. The transformation is a logical survival tactic: simplicity enables an internalized microbe to evade host defenses and reproduce itself in a hostile environment. It worked for Coccidioides in Los Angeles; at least 170 people caught in the Northridge quake got sick enough from breathing their spores to seek medical help. According to the CDC, this brought the 3-year statewide incidence of documented fungal infections to more than 4,500 cases.

Then something even stranger happened. A woman in Texas began complaining about a moldy odor that was undetectable to anyone else. But she was determined: "The whole world smells like a damp basement," she told one doctor after the other, but not a one could find a cause for this peculiar olfactory symptom. Infectious disease experts concluded that the woman's problem was imagined and referred her to a psychiatrist. The psychiatrist, puzzled by his new patient's single mysterious symptom --the odd smell she now said came from inside her head-- asked for a neurologic consult. He also ordered a CAT scan. An astounding picture emerged when this scan was compared to one taken a just few months earlier: the woman's brain was dissolving from front to back. It looked as if she was being lobotomized.

The neurologist, a microbiology buff, put the radiographic evidence and the patient's reports of a persistent "moldy" odor together and suspected a brain infection --not with bacteria, not with viruses, but with some sort of fungus.

This empiric diagnosis, as it turned out, was correct. Dr. Michael Rinaldi confirmed it in his laboratory at the University of Texas Health Science Center in San Antonio. Then Dr. Rinaldi began looking for other instances of unexpected fungal aggression. What he found helped change the way researchers view these organisms.

Subsequent articles described unusual bacterial diseases such as an particular nasty food poisoning caused by a strain of Escherichia coli that suddenly acquired a Shiga-like toxin and prion illness that made cows mad and then destroyed the brains of meat-eating humans. If the series were being written today, would certainly include Severe Acute Respiratory Syndrome (SARs).