Exploration of Antimicrobial, Antibiofilm and Antiquorum Sensing Activity of the Himalayan Yellow Raspberry ( Rubus ellipticus ) against Clinical Isolates of Escherichia coli and Staphylococcus aureus

Background: Management of ever growing multidrug resistant (MDR) bacteria becomes one of the biggest threats to public health worldwide. The situation is worsening due to lack of new generation antimicrobials in the arsenal of the clinicians. Development of new alternatives to the conventional antimicrobial agents is the need of the hour to control the menace of AMR. Plants based products are attractive alternatives with proven efficacy but needs scientific investigation to explore their potential antimicrobial, antibiofilm and antiquorum sensing activities against major bacterial pathogens of human and animals. The present study was conducted to explore the antimicrobial, antibiofilm and antiquorum sensing activity of aqueous and methanol extracts of leaf, flower, fruit and stem of the Himalayan yellow raspberry (Rubus ellipticus) against clinical isolates of Staphylococcus aureus and Escherichia coli. Methods: E. coli and S. aureus were isolated and identified from diarrhoeic pigs and poultry and mastitic milk of cattle of Mizoram, respectively. Leaf, flower, fruit and stem/bark of R. elipticus were collected from Mizoram and extracted by methanol and aqueous solvents. The antimicrobial activity and MIC was determined by well diffusion method and 96 wells microtiter plate method, respectively. Antibiofilm activity of plant extracts was determined in 96 well tissue culture plate. Antiquorum sensing activity was determined by disc diffusion method. Result: Methanol leaf extract exhibited antimicrobial activity against S. aureus with 19 mm and 7 mm zone of inhibition at 200 mg/mL and 12.5 mg/mL, respectively. Methanol fruit extract also showed antimicrobial activity against S. aureus only. Highest and lowest activities were observed at 200 mg/mL and 25 mg/mL concentrations with 15 mm and 7 mm zone of inhibition, respectively. No antimicrobial activities by either of the extracts were observed against E. coli isolates. The MIC of R. ellipticus methanol leaf and fruit extracts against S. aureus was 0.203125 mg/mL and 0.8125 mg/mL, respectively. The methanol leaf (86.60%) and stem (85.60%) extracts of R. ellipticus showed significant antibiofilm activity against S. aureus isolates, whereas methanol fruit (89.20%) extracts exhibited antibiofilm activity against E. coli isolates at the concentration of 0.05 mg/mL. Significant antiquorum sensing (QS) activities was exhibited by the methanol leaf extract of R. ellipticus at 200 mg/mL concentration against E. coli. This is the first ever report on antibiofilm and anti QS activities of the R. ellipticus plant extracts against E. coli and S. aureus bacteria.