Abstract:
Antimicrobial resistant poultry pathogens are responsible for treatment failure and
economic losses, and can also be a source of resistant zoonotic infections representing
a risk to human health. In 2006 the European Union banned the use of antibiotics
as growth promoters in farm animals and other regions are likely to follow suit.
Alternative products and strategies are sought to help maintain animal gut health
to reduce the prevalence of pathogens in the food chain. The minimum inhibitory
concentration (MIC) of organic and aqueous leaf extracts of Alchornea laxiflora, Ficus
exasperata, Morinda lucida, Jatropha gossypiifolia, Ocimum gratissimum, and Acalypha
wilkesiana were tested against bacterial poultry pathogens including Staphylococcus
aureus, Enterococcus faecalis, Salmonella spp., Escherichia coli, Campylobacter spp.,
and fungal species (Aspergillus fumigatus, Aspergillus flavus, and Candida albicans)
using a 2-fold serial microdilution method. Activity of extracts against biofilms of the
pathogens was done using a modified crystal violet staining in vitro assay. The safety
of extracts was determined against Vero and Caco-2 cells using a tetrazolium-based in
vitro assay. Acetone and cold water extracts of M. lucida had the best activity against
three bacteria (MIC = 0.05–0.07 mg/ml) and two fungal (MIC = 0.03–0.15 mg/ml)
organisms, respectively. The E. coli isolate and A. flavus were the most susceptible
bacteria and fungi, respectively. Caco-2 cells generally displayed higher selectivity index
(SI) values compared to Vero cells and average SI values against Vero and Caco-2 cells
for both bacteria and fungi ranged from 0.01 to 4.48 and 0.005 to 16.41, respectively.
All plant extracts had good anti-biofilm activity (>50%) against at least one organism.
The disruption of established biofilm growth by the plant samples proved to be more
difficult to achieve than efficacy against planktonic forms of bacteria. This study shows
that some of the plant species are potential candidates as alternative feed additives in
poultry production. In the future, a poultry feed trial to evaluate their in vivo efficacy as
herbal feed additives will be conducted.
