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It’s Not Just Mold — Toxic Bacteria in Water-Damaged Buildings

In a damp building, it’s not just dangerous molds that grow. Water-loving bacteria will spread as well. And that’s a big deal because these household bacteria can also cause toxic and inflammatory injury.

Wet Building, Hot Mess

One study by Andersson et al. performed a microbiology analysis of wet building materials to establish the dominant colonizers and the dominant toxins.

The dominant colonizers at water-damaged sites of the building were:

  • Stachybotrys — a mold
  • Penicillium — a mold
  • Actinomycetes — a bacteria
  • Gram negative bacteria
  • Mycobacteria

The dominant toxins were:

  • Endotoxin — a toxin made by gram negative bacteria
  • Beta-D-glucan — a toxic component on the mold cell wall
  • Satratoxin — a toxin made by Stachybotrys

Next the researchers created an extract from the wet building materials and exposed lung cells (from a cat) and sperm cells (from a boar) to the extract. Compared with extract from non-water damaged materials, the extract from wet building material exhibited a toxicity level nearly 200 times higher.

Mold versus Bacteria — Who’s the Bigger Baddie?

In another study by Huttunen et al. comparing the dangers of mold to bacteria, researchers measured the inflammatory and toxic responses of three harmful household molds and three harmful household bacteria. The three mold tested were Aspergillus versicolor, Penicillium spinulosum, and Stachybotrys chartarum. The three bacteria tested were Bacillus cereus, Pseudomonas fluorescens, and Streptomyces californicus.

The researchers exposed (mouse and human) macrophages, a type of immune cell, and (human) lung cells to one of these six microbes. All the bacteria increased three inflammatory markers—tumor necrosis factor-α, interleukin-6, and interleukin- 1β in mouse macrophages.

By contrast, the molds caused less of a response.  Except for Stachybotrys, the other molds did not increase any of the inflammatory markers tested. Stachybotrys, meanwhile, increased interleukin-6 in the (human) lung cells.

Based on the equivalent number of bacterial cells and mold spores added to the cell cultures, the researchers determined the following rank in inflammatory potency:

  1. Pseudomonas fluorescens
  2. Streptomyces californicus
  3. Bacillus cereus
  4. Stachybotrys chartarum
  5. Aspergillus versicolor
  6. Penicillium spinulosum

In summary, the bacteria made a clean sweep of the podium—with even Stachybotrys showing less inflammatory potential than the household bacteria.

With typical academic restraint, the authors of this study wrote:

“These data suggest that bacteria in water-damaged buildings should also be considered as causative agents of adverse inflammatory effects.”


  1. Andersson, Maria A., et al. “Bacteria, molds, and toxins in water-damaged building materials.” Applied and environmental microbiology 63.2 (1997): 387-393.
  2. Huttunen, Kati, et al. “Production of proinflammatory mediators by indoor air bacteria and fungal spores in mouse and human cell lines.” Environmental Health Perspectives 111.1 (2003): 85-92.