Antibacterial properties of plant essential oils

The antimicrobial properties of essential oils (EOs) have been recognised for centuries and, with growing demand from changes in legislation, consumer trends and increasing isolation of antibiotic resistant pathogens, alternatives to chemical-based bactericides need to be found. Citrus oils not only lend themselves to use in food but also are generally recognised as safe (GRAS) and have been found to be inhibitory both in direct oil and vapour form against a range of both Gram-positive and Gram-negative bacteria. This group of oils may provide the natural antimicrobials that the food industry requires to fulfil both its requirements and those of the consumer.

Potential antimicrobial uses of essential oils in food: is citrus the answer?

Converting citrus wastes into value-added products: Economic and environmently friendly approaches

Carvacrol, citral and geraniol showed potent antibacterial activity against Salmonella typhimurium and its rifampicin-resistant (RifR) strain as determined in txyptic soy broth and by zone of inhibition on agar-based medium. Carvacrol had the most potent bactericidal activity, with minimum inhibitory and bactericidal concentrations (MIC and MBC) of 250 μg/mL for both tester strains. When tested at 0.5, 1.5 and 3.0% in 1% Tween 20 for bactericidal activity against RifR-S. typhimurium inoculated on fish cubes, carvacrol at 3.0% completely killed the inoculated bacteria, while geraniol killed most of the bacteria, and citral killed the least. Carvacrol and geranial showed potent antibacterial activity at 1.5%. Bactericidal activity became more evident as storage of fish cubes at 4°C lengthened. The comparable inhibition of these strains of Salmonella and species of Gram-negative bacteria by carvacrol and geraniol support their application as potential antibacterial agents in food systems.

Antibacterial Activity of Carvacrol, Citral, and Geraniol against Salmonella typhimurium in Culture Medium and on Fish Cubes

The modern antibiotic era can be said to have opened on February 12, 1941, with the first clinical trial of penicillin. Within a couple of years man had at last, after eons of adventitious searching, a truly effective and safe agent for the treatment of many systemic bacterial infections. This was shortly followed by the introduction of one after another of the major antibiotic substances which remain the mainstay of clinical therapy of infectuous diseases to this date. Intensive screening of fermentation liquors derived from various microbes, principally fungi and streptomycetes, has resulted in literature descriptions of more than 2,000 Individual antibiotics to date, and It has been estimated that more than 20,000 analogs of 6-amino- penicillante acid alone have been made by chemists working tn close collaboration with biochemists and microbiologists. Several of these substances are currently on the market.

Antimicrobial Agents from Higher Plants

inhibitory effect of essential oils of orange
and lemon oil and the antibiotics tylosin and nisin was tested
on bacteria and fungi in nutrient media. Though the degree
of inhibition varied with the culture, orange oil was a more
effective antimicrobial agent than lemon oil. All other conditions
being identical, 2,000 ppm of orange oil had an effect
similar to 10 ppm of tylosin, on all the gram-positive cultures
tried, including the spores of Bacillus mbtilis. Moreover,
orange oil was the only additive that showed inhibition of
growth of the gram-negative cultures, excepting Serratia
nzarcescens. Yeasts, in general, were more sensitive than bacteria
to orange oil, the effective dose being 500 ppm, at a
cell concentration of 1 million/ml. This was a definite advantage
over the antibiotics, which had no action on fungi.
Though not so sensitive as the yeasts, the molds were also
suppressed by orange oil at 2,000 ppm. The possibility of
using orange oil as a preservative in foods is indicated.

T. C. Soumithri

Papers

Antimicrobial Action of Citrus Oils