Toxicity of Ocimum americanum L. extracts against Aedes aegypti larvae (Diptera: Culicidae) and their impact on insecticide resistance.

Mosquitoes are a key threat to millions of people worldwide. They spread the pathogens that cause deadly diseases among humans and animals. Synthetic pesticides are the best agents to control mosquitoes, but they cause several problems for the environment as well as public health. Continuous usage of commonly available insecticides develops multiple resistances among pests. In search of alternatives to synthetic pesticides, botanicals could be one of the best alternatives to control mosquitoes. The present study explores the insecticidal activity of Ocimum americanum against Aedes aegypti larvae and their effect on detoxification enzymes. Leaves of O. americanum were sequentially extracted using hexane, chloroform, and methanol. Among these, hexane extract showed 100% larvicidal activity at 1 g/L concentration for 24 h and the LC50 value was 0.3 g/L. The phytochemical screening of hexane extract was performed through gas chromatography-mass spectrometry analysis, which showed 27 compounds. The major compounds are squalene (13.03%), camphor (9.77%), and 1-Iodohexadecane (8.02%). The toxicity of active hexane extract was tested against third instar larvae of Chironomus costatus (nontarget organism). Results revealed less toxicity (12.2%) at 1 g/L concentration on the nontarget organism. The enzyme activity of acetylcholinesterase and ß-carboxylesterase was significantly inhibited by the hexane extract. The present study reveals the insecticidal potential of O. americanum with minimum effects on nontarget organisms. The O. americanum extract inhibited the activity of A. aegypti's major insecticide-resistant enzymes. O. americanum could be one of the best alternatives to controlling mosquitoes.

In vitro antibacterial activity of some plant essential oils.

BACKGROUND: To evaluate the antibacterial activity of 21 plant essential oils against six bacterial species. METHODS: The selected essential oils were screened against four gram-negative bacteria (Escherichia coli, Klebsiella pneumoniae, Pseudomonas aeruginosa, Proteus vulgaris) and two gram-positive bacteria Bacillus subtilis and Staphylococcus aureus at four different concentrations (1:1, 1:5, 1:10 and 1:20) using disc diffusion method. The MIC of the active essential oils were tested using two fold agar dilution method at concentrations ranging from 0.2 to 25.6 mg/ml. RESULTS: Out of 21 essential oils tested, 19 oils showed antibacterial activity against one or more strains. Cinnamon, clove, geranium, lemon, lime, orange and rosemary oils exhibited significant inhibitory effect. Cinnamon oil showed promising inhibitory activity even at low concentration, whereas aniseed, eucalyptus and camphor oils were least active against the tested bacteria. In general, B. subtilis was the most susceptible. On the other hand, K. pneumoniae exhibited low degree of sensitivity. CONCLUSION: Majority of the oils showed antibacterial activity against the tested strains. However Cinnamon, clove and lime oils were found to be inhibiting both gram-positive and gram-negative bacteria. Cinnamon oil can be a good source of antibacterial agents.