The antimicrobial activity of six Ocimum species against human microbial pathogens

Title : The antimicrobial activity of six Ocimum species against human microbial pathogens

Abstract:

Multidrug resistance among human pathogens is driven by antibiotic overuse and genetic factors. It remains a global crisis, causing over a million deaths each year. Chemical and gene-based therapies are often costly. Plant-based alternatives may offer a more affordable solution. Basil (Ocimum spp.) is widely used in medicine for its essential oils and phenolic compounds, which have antimicrobial properties. This study evaluated the antimicrobial activity of six Ocimum species against two human pathogenic bacteria. Growth inhibition was assessed by measuring turbidity with a Bioscreen C microplate reader. Crude methanolic extracts and essential oils at 1% w/w were dissolved in DMSO and tested against Streptococcus pyogenes and Escherichia coli. Streptomycin was used as the standard antibiotic for comparison.

Ocimum x. africanum methanolic extracts (mean OD 0.08) and O. campechianum essential oil (mean OD 0.15) significantly inhibited both bacteria. Methanolic and essential oil extracts of O. americanum, O. basilicum, O. gratissimum, and O. tenuiflorum, with OD values between 0.06 and 0.26, inhibited bacterial growth as effectively as or better than streptomycin. The leaf extract of PI 500947, with mean ODs of 0.08 and 0.15 for S. pyogenes and E. coli, showed the highest inhibitory effect. The essential oil extract of PI 500945 (O. americanum) inhibited S. pyogenes (mean OD, 0.21) and E. coli (mean OD, 0.18). The methanolic extracts of O. basilicum accessions PI 652071 and PI 172996 had mean OD values of 0.16 and 0.06, respectively, against S. pyogenes and E. coli.

The essential oil extract of accession PI 358472 inhibited S. pyogenes (mean OD, 0.20) and E. coli (mean OD, 0.18) more effectively than other O. basilicum accessions. Only the essential oil extract of O. campechianum inhibited both bacteria. The methanolic and essential oil extracts of O. gratissimum accessions PI 652067, PI 652069, PI 211715, and PI 500952 inhibited both S. pyogenes and E. coli. The methanolic extracts of the O. tenuiflorum MSR1 accession showed mean OD values of 0.12 and 0.06. These demonstrated the highest inhibition of S. pyogenes (mean OD, 0.12) and E. coli (mean OD, 0.06), respectively. In this study, extracts from O. x africanum, O. campechianum, O. americanum, O. basilicum, O. gratissimum, and O. tenuiflorum inhibited S. pyogenes and E. coli at levels comparable to or exceeding streptomycin in cell culture. These findings suggest that Ocimum species are promising sources of phytochemicals for the development of plant-based antimicrobials to combat multidrug-resistant pathogens.

Biography:

Dr. Srinivasa Rao Mentreddy, an Indian-born American citizen, is a Professor of crop science at Alabama A&M University, Alabama, USA. His research focuses on developing cover crop-based sustainable crop production practices for vegetable and medicinal herbs in the open field and agroforestry systems, evaluating low-temperature plasma for ensuring food safety and improving crop productivity, and climate-smart agricultural practices using cover crops and alley cropping. Dr. Mentreddy earned a BS and MS in Agriculture from the Andhra Pradesh Agricultural University, India, and a Ph.D. in Agronomy from the University of Tasmania, Australia. Dr. Mentreddy is well-published, with about 48 peer-reviewed journal articles, five book chapters, and more than 196 conference proceedings abstracts.