Antimicrobial activity of essential plant oils and their major components

Abstract

Development of bactericides and fungicides in terms of isolation and identification of substances is an important area of research. Presently, under the concept of integrated pest management, all possible plant pest and disease control methods are integrated to minimize the excessive use of synthetic chemicals and also the incidence of disease. The potential of various essential oils against Gram-positive and Gram-negative bacteria and fungi is being actively investigated in various laboratories across the world. Rice the most important crop, suffers from huge yield losses due to blast and blight diseases. Most of the labs have focussed to use transgenic approaches, the use of environmentally friendly natural products, as disease control strategies. In this context, we propose to evaluate the antimicrobial properties of essential oils and their ability to control diseases of rice. Seven Essential oils from seven different plants were selected for the study. The antimicrobial activity was assessed in terms of their antibacterial activity towards non-pathogenic bacteria and pathogenic drug resistant bacteria by means of their ability to sensitize the drug resistant bacteria in plasmid curing and, ß-lactamase inhibition and as antifungal agents. In conclusion, out of the seven essential oils used, lemongrass, palm rosa and eucalyptus were found to be good antimicrobial agents.

Keywords: Anti microbial activity; Bacterial; Gram; Gram + bacteria; Natural products; Plant essential oils; Rice diseases.

Figure 1

Comparison of MBCs of lemon grass oil and its major component citral. a to e: Comparison of minimum bactericidal concentrations of lemon grass oil and its major component citral, with antibiotics viz- ciprofloxacin, gentamicin, ampicillin, streptomycin and chloramphenicol respectively, against various Gram + and Gram- bacteria. The inverses of MBC values are represented in the figures to have a better presentation.

Figure 2

Comparison of MBCs of Palm Rosa oil and its major component Geraniol. a to e: Comparison of minimum bactericidal concentration values of palm rosa oil and its major component geraniol, with antibiotics viz- ciprofloxacin, gentamicin, ampicillin, streptomycin and chloramphenicol respectively against various Gram + & Gram –ve bacteria. The inverses of MBC values are represented in the figures to have a better presentation.

Figure 3

Comparison of MBCs of Eucalyptus oil and its major component Citronellal. a to e: Comparison of MBC values of Eucalyptus oil and its major component citronellal, with antibiotics viz., ciprofloxacin, gentamicin, ampicillin, streptomycin and chloramphenicol respectively, against various Gram + and Gram –ve bacteria. The inverses of MBC values are represented in the figures to have a better presentation.

Figure 4

Comparison of minimum bactericidal concentration values of essential oils and their major components against various Gram + and Gram –ve bacteria. a: Comparison of minimum bactericidal concentration values of essential oils lemon grass, palm rosa, eucalyptus against various Gram + and Gram –ve bacteria. The inverses of MBC values are represented in the figures to have a better presentation. b: Comparison of minimum bactericidal concentration (MBC) values of major components citral, geraniol and citronellal against various Gram + and Gram –ve bacteria. The inverses of MBC values are represented in the figures to have a better presentation.

Figure 5

Time course of lethal action of lemon grass, palm rosa and eucalyptus. a–c: Time course of lethal action of essential oils lemon grass, palm rosa and eucalyptus against E. coli (a), S. aureus (b) and X. oryzae (c).

Figure 6

Time course of lethal action of essential oils geranium and citronella. a–c: Time course of lethal action of essential oils geranium and citronella against E.coli (a), S. aureus (b) and X. oryzae (c).

Figure 7

Time course of lethal action of citral, geraniol and citronellal. a–c: Time course of lethal action of major components citral, geraniol and citronellal against E. coli (a), S. aureus (b) and X. oryzae (c).

Figure 8

Ability of essential oils & their major components in curing pBR322. Lane 1: DNA/Hind III Digest (Bangalore Genei), Lane 2: pBR 322 from untreated E. coli HB101 (Control), Lane 3: pBR322 from lemon grass oil treated E. coli HB101, Lane 4: pBR322 from palm rosa oil treated E. coli HB101, Lane 5: pBR322 from eucalyptus oil treated E. coli HB101, Lane 6: pBR322 from geranium oil treated E. coli HB101, Lane 7: pBR322 from citronella oil treated E. coli HB101, Lane 8: pBR322 from citral treated E. coli HB101, Lane 9: pBR322 from geraniol treated E. coli HB101, Lane 10: pBR322 from citronellal treated E. coli HB101, Lane 11: 1 kb DNA ladder Mix (MBI Fermentas).

Figure 9

Zone of inhibition of M. Grisea by various essential oils. (A) zone of inhibition of M. grisea around the paper disks loaded with 4 μl and 8 μl of lemon grass essential oil, (B) zone of inhibition of M. grisea around the paper disks loaded with 4 μl and 8 μl of citral, (C) zone of inhibition of A. niger around the paper disks loaded with 4 μl and 8 μl of lemon grass essential oil, (D) zone of inhibition of A. niger around the paper disks loaded with 4 μl and 8 μl of citral, (E) zone of inhibition of F. udum around the paper disks loaded with 4 μl and 8 μl of lemon grass essential oil, and (F) Represents the zone of inhibition of F. Udum around the paper disks loaded with 4 μl and 8 μl of citral.

Figure 10

Biomass inhibition of fungi by essential oils. Biomass inhibition of Aspergillus niger (a), Fusarium udum (b), Fusarium oxysporum (c) and Magnoporthe grisea (d) in presence of essential oils lemon grass, palm rosa, eucalyptus, geranium and citronella. Biomass inhibition of A. niger (e), F. udum (f), F. oxysporum (g) and M. grisea (h) in presence of essential oil major components citral, geraniol and citronellal.