The Isolation of Antimicrobial Resistant Aeromonas spp. from Aquaculture Samples and their Susceptibility to Medicinal Plant Extracts

Aeromonas spp, ubiquitous in both terrestrial and aquatic environments are becoming renowned as enteric pathogens of serious public health concern as they have a number of virulence and resistant determinants that are linked to both human and aquatic diseases due to consistent and incorrect use of antibiotics in aquaculture. The effect of crude aqueous and ethanol extracts of some medicinal plants on antimicrobial resistant Aeromonas spp. isolated from aquaculture water and fish samples was studied. Two hundred and forty (240) Aeromonas isolates, made up of 168 Aeromonas hydrophila and 72 Aeromonas salmonicida, were recovered from aquaculture water and fish gill samples collected from different commercial fish ponds using selective media. The isolates were assessed for their antibiotic susceptibility against ten (10) conventional antibiotics using the Kirby-Bauer technique. Extracts from three medicinal plants, Vernonia amygdalina, Ocimum gratissimum and Garcinia kola were also analyzed for their antimicrobial effects on the isolates that were resistant to the conventional antibiotics. Aeromonas hydrophila isolates expressed the highest resistant rates of 100%, 78.6% and 70.8% to aztreonam, cefotaxime and neomysin respectively, and the A. salmonicida isolates also had a similar trend of high resistant rates of 100%, 87.5% and 77.8% to aztreonam, neomysin and cefotaxime respectively. Antimicrobial resistant analyses with the plant extracts showed 100% inhibition of the isolates at 100 mg/ml for both aqueous and ethanol extracts. Phytochemical screening identified the presence of certain phytochemicals like alkaloids, saponins, tannins, flavonoids, steroids and glycosides which could have accounted for the antimicrobial effects of the plant extracts under study. It can be inferred then, that extracts from Vernonia amygdalina, Ocimum gratissimum and Garcinia kola can inhibit resistant aquaculture Aeromonas isolates and so can present an alternative source of antimicrobials in the effort to combat the increasing incidence of antimicrobial resistance in aquaculture.