Journal of the Medical Association of Thailand Vol 93, No 12:DECEMBER 2010 (SUPPL.7) 0125-2208 93 12 2010 Dec Antibacterial and Antifungal Activities from Siamese Crocodile Blood 58 EN Ratree Leelawongtawon Jindawan Siruntawineti Win Chaeychomsri Chisanucha Sattaponpan Original Article To evaluate the in vitro antimicrobial activity of the Siamese crocodile blood against bacteria and fungi. Thirty Siamese crocodile blood samples including freeze dried whole blood (FDWB), fresh serum(FS), and freeze dried serum (FDS) were evaluated for antimicrobial susceptibility and MIC values against ATCC-registeredstrains of nine bacterial species and two fungal species and one fungus isolated from a clinical specimen, by using thestandard broth microdilution method and a modified resazurin microtiter plate assay. The result showed that FS (80 mg/ml) and FDS (100 mg/ml) inhibited Gram negative bacteria including Enterobacteraerogenes ATCC 13048, Escherichia coli ATCC 25922, Klebsiella pneumoniae ATCC 27736, Salmonella typhimuriumATCC 13311 and Pseudomonas aeruginosa ATCC 27853 with the susceptibility rate at 23.30%, 10.00%, 40.00%, 70.00%,and 86.67%, respectively for FS, and 30.00%, 10.00%, 43.33%, 76.67% and 90.00%, respectively for FDS. The MIC andMBC were in the range of 12.50-100.00 mg/ml and 25.00-100.00 mg/ml, respectively. FS and FDS also inhibited Cryptococcusneoformans 250309 and Aspergillus niger with the susceptibility rate at 90.00% and 80.00%, respectively for FS and100.00% and 83.33%, respectively for FDS. The MIC was in the range of 25.00-100.00 mg/ml. However, FS and FDS didnot inhibit Gram positive bacteria and did not kill fungi. FDWB (100 mg/ml) could neither inhibit bacteria nor fungi.