Scanning Electron Microscopic Analysis and Inhibitory Effect of Oroxylum indicum Extract Against Clinical Isolated Penicillin, Aminoglycoside and Lincosamide Resistant Pasteurella multocida

Pasteurella multocida is a pathogenic bacterium which causes severe diseases in mammals and avian including haemorrhagic septicaemia in cattle and buffaloes and respiratory disease in commercial farm pigs. Oroxylum indicum extracts have previously been reported to promote inhibitory effects against some clinical isolated pathogenic bacteria. In this study, O. indicum fruit extract was qualitatively controlled for total phenolic, total flavonoid and flavone contents determined by Folin-Ciocalteu, aluminium chloride and high performance liquid chromatography (HPLC) methods, respectively. Total phenolic and total flavonoid contents of the extract were 4%w/w gallic acid equivalent (GAE) and 5%w/w quercetin equivalent (QE) of the dried extract, respectively. The contents of the major flavones; baicalin, baicalein and chrysin were found to be 0.40, 0.36 and 1.12 %w/w of dried extract, respectively. The extract showed in vitro antibacterial effects against clinically isolated aminoglycoside and lincosamide resistant Pasteurella multocida with half-maximal inhibitory concentration (IC50) of 14.98 ± 0.35 mg/ml and the minimum inhibitory concentration (MIC) was 29.24 ± 0.05 mg/ml. Scanning electron microscopic analysis of the effects of O. indicum fruit extract against P. multocida suggests the formation of bacterial morphological changes, cell wall disruption, content leakage, abnormal groups of cell aggregations, and cell lysis within 15 h. The results suggest the inhibitory potential of O. indicum fruit extract against antibiotic resistant Pasteurella multocida. The extract could be further developed as an alternative or co-therapy in the treatments of animals and human P. multocida related diseases.