Phytogenics as an Alternative to Antibiotics: Chemical Mechanism behind Antimicrobial Activity of Essential Oils

Abstract

Since the 1950s, antibiotics have been the “silver bullet” for the
treatment of diseases in both the medical and livestock industries.
The use of subtherapeutic antibiotics in broilers not only
prevents disease outbreaks but also increases meat yield and feed
conversion.1 The mode of action for the added growth promoter
effects of antibiotics stems from their ability to control microbial
populations in the gut, decreasing toxic microbial byproducts
and limiting competition for nutrients in the gastrointestinal tract
(GIT).2,3 These growth promoting effects have made antibiotics a
common feed additive in the poultry industry.4 However, decades
of exposing microorganisms to low doses of antibiotics has created
a selection pressure for antibiotic-resistant bacteria.5 In a 2017
study in Ghana, over sixty percent of Staphylococci isolates from
poultry farms and farm workers were resistant to multiple antibiotics,
including tetracycline, one of the most common antibiotics
in the poultry industry.6 The European Union banned the use of
food animal growth-promoting antibiotics in 1986. In the USA,
the guidelines for Industry issued by the Center for Veterinary
Medicines of the Food and Drug Administration (FDA, 2012)
recommend use of antibiotics only for the prevention, control
and treatment of infections in animals but not for the promotion
of growth, increased performance, and improved feed efficiency
Alternatives to antibiotics are, therefore, needed in order to continue
the efficiency and sustainability of the poultry production.
A promising alternative is phytogenic essential oil. In this editorial,
we will review how the structure of phytochemicals within
essential oils contributes to the antimicrobial activity and growth
promotion in broilers.