Comparison of Tissue Burden Assessment by Galactomannan EIA and Quantitative Culture in a Guinea Pig Model of Invasive Pulmonary Aspergillosis
Background: The ability to accurately assess fungal tissue burden in animal models of invasive pulmonary aspergillosis (IPA) is a controversial topic. This led us to examine two different evaluation methodologies for their ability to detect fungal burden in guinea pigs (GP). Methods: Three groups of immunosuppressed GP (n=78) were challenged with nebulized suspensions of Aspergillus fumigatus (AF293) in either an acrylic inhalation chamber (10^9 CFU/ml) or a Madison inhalation chamber (10^10 CFU/ml) for 1 h. Fungal burden was determined for lung, brain, liver, kidney and spleen using standard quantitative culture (CFU) and galactomannan EIA (GM) at selected time points over 8 or 9 d. Selected samples from the acrylic chamber studies were subjected to histological examination. Results: In the acrylic chamber, a 1 log10 drop in lung tissue burden was seen in CFU from d 4 to 8, however, the GM index showed an approximate 1 log10 increase in fungal burden during this time. Additionally, median fungal burden in extra-pulmonary tissues, (brain, liver, kidney and spleen) dropped from 2.5 to <1 (log10) as assessed by CFU. Assessment by GM index revealed persistently elevated GM levels for these same tissues over the 5 day time course as compared to the 1 h threshold level. Similar results were noted in the Madison chamber study: a decrease in lung tissue burden was seen in CFU from challenge to d 9, while the lung GM index showed GM levels increasing from challenge though days 5 to 9. Median fungal burden in the kidney dropped from 2.5 (log10) at d 3 to undetectable levels by d 9 as assessed by CFU. Assessment by GM index revealed steadily elevated GM levels for the kidneys from 7 to 9 d as compared to the 1 h threshold level. Histological examination of lung tissue at d 0 revealed conidia in the alveoli, with no conidia seen in kidney tissue at this time. Histology by d 5 revealed the extensive presence of hyphal tissue invasion in the lungs but with no organisms detected in the kidney. Conclusions: Assessment of Aspergillus tissue burden by CFU alone may lead to an underestimation of fungal burden in IPA, particularly in the lungs but also in extra-pulmonary tissues. Utilization of multiple tissue burden quantitation methods may provide more precise assessment of fungal load, and may lead to improved assessment of diagnostic and therapeutic strategies in IPA.
- AAA 2nd (2006)
Full conference title:
2nd Advances against Aspergillosis