Comparison of Tissue Burden Assessment by Galactomannan EIA and Quantitative Culture in a Guinea Pig Model of Invasive Pulmonary Aspergillosis

Kirkpatrick W.R.1, Vallor A.C.1, McCarthy D.I.1, Najvar L.K.1, Bocanegra R.1, , Fothergill A.W.1, Graybill J.R.1, Patterson T.F.1

Full title: 

Comparison of Tissue Burden Assessment by Galactomannan EIA and Quantitative Culture in a Guinea Pig Model of Invasive Pulmonary Aspergillosis

Author address: 

1The University of Texas Health Science Center, San Antonio, TX, USA

Abstract: 

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.
2006
    • AAA 2nd (2006)

abstract No: 

P072

Full conference title: 

2nd Advances against Aspergillosis