Morphological, molecular and histopathological characterization of fungi isolated from formalin-fixed animal cadavers and possible sources of contamination from anatomy laboratory, COVAB, Makerere University

Abstract

Animal cadavers play a crucial role as a fundamental instructional resource in the training of anatomists and veterinary students. While formalin is known for its potent antimicrobial properties, certain fungi continue to grow in the presence of formalin. This study aimed at identifying the fungal species that grow on formalin-fixed animal cadavers and internal tissues of fixed cadavers using morphological molecular and histopathological techniques. In addition, the study identified potential environmental sources of contamination. Finally, this study also identified fungal taxa carrying the adhc and fdh genes associated with formalin degradation. The fungi isolated from formalin-fixed animal cadaver tanks, the environmental air from the store, and the embalming room floor, were characterized using PCR amplification and sequencing of the internal transcribed spacer (ITS) region, β-tubulin (Bt), adhc, and fdh genes, together with morphological characterization. The resulting sequences were analyzed using BLAST, and species identification was confirmed by comparison with representative sequences in GenBank. Formalin fixed tissues were processed in the histopathology laboratory and stained with Gridley’s stain. A total of ten fungal isolates belonging to three genera; Aspergillus, Penicillium, and Scedosporium were identified, with Aspergillus being the predominant genus (8/10). Seven isolates originated from the three formalin-fixed animal cadavers. No fungal growth was detected in the distilled water used to prepare the 10% formalin. Two isolates of A. flavus were obtained from the environmental air (store), and one Penicillium species was isolated from the embalming room floor. β-tubulin gene sequencing confirmed Aspergillus niger (isolate 2) and Aspergillus flavus var. flavus (isolate 9). The fdh gene was detected in two Aspergillus isolates whereas adhc formaldehyde-degrading gene was detected in four Aspergillus isolates. The Penicillium isolate contained both genes. Histopathological examination revealed fungal mycelia of Aspergillus in formalin-fixed tissues without accompanying inflammation, indicating post-fixation invasion. The detection of fungal species capable of degrading formaldehyde presents a potential veterinary public health concern. Similar studies should be carried out in other laboratories that use formalin fixed tissues to determine whether comparable contamination challenges exist.