CINCINNATI—Stachybotrys chartarum has received a lot of attention from the lay media as a “killer mold” that infests buildings and poses a serious health risk. But, determining the extent to which inhalation of S chartarum—or other molds—is harmful has been hampered by the lack of a biomarker that could confirm or quantify exposure.

Researchers working with the Environmental Protection Agency have recently developed two enzyme-linked immunosorbent assays (ELISAs) to measure stachylysin, a hemolysin produced by S chartarum.[1] If proven accurate in large trials, these ELISAs would offer physicians a way to more precisely investigate what, if any, harmful effects result from S chartarum exposure. The researchers also hope that the new ELISAs could also be used as a model for how environmental exposure to other molds could be studied.

THE ASSAYS

Both ELISAs use an antistachylysin antibody to measure hemolysin levels in a variety of samples. They were performed in a similar manner except that the second assay included incubation of the sample.

Strains of S chartarum were taken from houses that were part of a separate investigation of pulmonary hemosiderosis. The presence of the hemolysin was also measured in dust samples from schools, homes, and commercial buildings—including a dust sample from the home of a child with pulmonary hemosiderosis. In addition, rat pups were exposed intranasally to S chartarum, and then serum levels of stachylysin were measured.

Serum samples were also collected from five people with known exposure to S chartarum who complained of feeling ill. These samples were compared with sera from five controls with no known exposure to S chartarum.

Both assays were highly selective for stachylysin. ELISA I required an analysis time of four hours and had a linear range of 10 to 300 ng/mL and a limit of detection of 20 parts per billion. This assay was useful when analyzing samples with high levels of exposure to S chartarum. ELISA II was better at detecting low levels of exposure. It required a two-day incubation period and had a linear range of 1 to 30 ng/mL and a limit of detection of 2 parts per billion.

STACHYLYSIN LEVELS SIGNIFY EXPOSURE

The concentration of the hemolysin in pooled sera from adults who were exposed to S chartarum in the workplace was 371 ng/mL, but it was undetectable in the control group. Concentrations in rats exposed to S chartarum intranasally averaged 10.9 ng/mL but were highly variable.

If dusts with high concentrations of the hemolysin are inhaled, they may travel into the nasopharynx and even reach the lungs, the investigators suggested. After observing hemolysin levels in sera from people working in water-damaged buildings, they believe that it can also get into the bloodstream.

The investigators noted that serum levels of stachylysin may be used to gauge human exposure to S chartarum. “If stachylysin is relevant to negative human health effects, its measurement in dust or other environmental samples by ELISA may assist in the risk assessment and ultimate risk management concerning indoor exposures to S chartarum,” they wrote.

—Gale Jurasek