Antimicrobial and Antibiofilm Activities of Methanol Leaf Extract of Citrus maxima against Clinical Isolates of Multidrug Resistant Staphylococcus aureus

Background: Mitigation process to curb the ever increasing problem of antimicrobial resistance through development of new class of antimicrobials is slow and costly affairs. Research on alternative to conventional antimicrobials using plant based products as good source of numerous phytochemicals have potential to cope up the antimicrobial resistance. The present study was formulated on detection of in vitro antimicrobial and antibiofilm properties of methanol leaf extract of Citrus maxima against clinical isolates of Staphylococcus aureus. Methods: Leaves of Citrus maxima plants were collected from the campus of College of Veterinary Sciences and Animal Husbandry, Central Agricultural University, Aizawl, Mizoram and processed for preparation of methanol crude extract. The plant extracts were evaluated for their phytochemical and antioxidant properties using DPPH (2, 2-Diphenyl-1-picrylhydrazyl) method. Twenty well characterized biofilm producing and multidrug resistant Staphylococcus aureus strains recovered from milk of mastitic cows from Mizoram were received from the cultural repository of the department. The plant extracts were subjected to determine their antimicrobial and antibiofilm activities against all the bacterial isolates including S. aureus (ATCC 29213) by in vitro agar well diffusion method and 96 well microtiter plate methods, respectively. The MIC value of the plant extracts were determined by microdilution method. Result: In the methanol leaf extract of C. maxima alkaloids, glycosides, terpenoids, tannin and phenol and flavonoids were detected by qualitative analysis. Saponin, protein, free amino acids, steroids and carbohydrates were not detected. The free radical scavenging potential of the extract was found to be 10.66±1.84% to 36.10±1.98%, which was comparatively lower than ascorbic acid (83.39±0.13% to 89.76±0.24%). A total of 8 (40.0%), 5 (25.0%) and 7 (35.0%) strains were recorded as weak, moderate and strong biofilm producer. Maximum antibacterial activity against standard culture was observed with the zone of inhibition of 18 mm at 200 mg/mL concentration and MIC value at 25 mg/mL. Maximum antimicrobial activities against clinical isolates were recorded with 11.8±1.13 mm zone of inhibition at 200 mg/mL and MIC value at 25 mg/mL. The clinical isolates exhibited highest (85.94±1.00%) biofilm inhibition at 6.25 mg/mL. To the best of our knowledge, this is the first-ever report on antibiofilm and antioxidative activities of C. maxima leaf extracts against any bacteria.