RESUMEN
Antimicrobial substances in serum include circulating complement proteins and acute phase proteins (APPs). We identified gene sequences for APPs, haptoglobin (Hp), C-reactive protein (CRP) and serum amyloid A (SAA) in marsupial genomes. Hp and SAA levels were measured in red-tailed phascogale (Phascogale calura) sera using commercially available assays. Hp levels were higher in males than females, while SAA levels suggest the phascogales used in this study were healthy. Serum was co-cultured with four bacterial species. Bacterial growth was inhibited after incubation at 37°C, however effectiveness differed with bacteria and incubation time. The least amount of bacterial growth was noticed after introduction to K. pneumoniae, and most when introduced to P. aeruginosa. Despite marsupials not having mature immune tissues at birth, and unable to mount specific immune responses, this study suggests other immune strategies, such as APPs in serum likely aid marsupials in their defence against pathogens.