EFFECT OF LEMONGRASS OIL AND CITRAL IN COMBATING ANTIBIOTIC RESISTANCE IN STAPHYLOCOCCUS AUREUS ISOLATES FROM BOVINE MASTITIS
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Date
2020-03-24
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COLLEGE OF VETERINARY AND ANIMAL SCIENCES MANNUTHY, THRISSUR
Abstract
Antibiotic resistance imposes severe therapeutic and economic burden in the
treatment of mastitis and may threaten the success of antimicrobial chemotherapy.
Essential oils and their constituents are gaining great importance in the recent
times as promising antimicrobial and resistance modifying agents. Hence, the
present study was conducted to evaluate antibacterial, resistance modifying and
antibiofilm activities of lemongrass oil (LGO) and its major active principle citral,
individually as well as in combination with methicillin/oxacillin against
methicillin resistant Staphylococcus aureus (MRSA) isolated from bovine mastitic
milk. Among the 80 mastitic milk samples collected, 58 S. aureus organisms were
isolated using culture and biochemical characteristics, in which 16 isolates were
identified as MRSA by antibiogram. Nevertheless, only six isolates among the
MRSA revealed presence of mecA and hence selected for further evaluation study.
The test substance LGO was subjected to GC-MS analysis prior to evaluation and
level of the citral content was found to be 72 per cent approximately. The findings
of the study indicated significant antimicrobial activity of LGO and citral as
evident from their minimum inhibitory concentration (MIC) and diameter of zone
of inhibition. Lemongrass oil and citral produced remarkable inhibition of biofilm
formation and preformed biofilm, manifested as significantly reduced minimum
biofilm inhibitory concentration (MBIC) and minimum biofilm eradication
concentration (MBEC). Furthermore, the combination therapy of LGO and citral
with methicllin/oxacillin, as appraised by checkerboard method revealed
synergistic interaction in both antimicrobial and antibiofilm assays, establishing
the implication of combination strategy in mitigating antibiotic resistance.
Moreover, in silico molecular docking study revealed that citral possesses binding
affinity for mecA via hydrogen bond and hydrophobic interactions. Thus, present
findings are indicative of the vital role of LGO and citral in alleviation of
methicllin/oxacillin resistance via its synergistic effect with the resistant
antibiotics, down regulation of mecA and antibiofilm activities.
Description
Thesis Submitted in the partial fulfillment of the requirement for the degree of Master of Veterinary Science in Veterinary Pharmacology and Toxicology