Abstract:
Sweet orange (Citrus sinensis), a key fruit species, is considered as a primary ingredient in herbal
medical formulations against ailments such as food borne diseases. Sour orange (C. aurantium) is
also very famous as a medicinal plant. There are six commonly grown sweet orange cultivars in Sri
Lanka (Arogya, Bibila sweet, MKD, Sisila, BAN and MT) but the antibacterial activity present in
their fruit juice is not well documented. Therefore, the present study was conducted to characterize
the antibacterial activity of the fruit juice of these sweet oranges in comparison to sour orange and
also to establish DNA barcodes for the tested cultivars for precise identification. Fruit juice was
collected from sweet orange cultivars and sour orange and antibacterial activity was measured
against three model pathogenic bacterial species, Escherichia coli, Staphylococcus aureus and
methicillin-resistant S. aureus. After employing filter paper disc method, the diameter of zone of
bacterial inhibition (DZI) was measured as the parameter of antibacterial activity. The genomic
DNA was extracted from all the tested plants and PCR amplified using trnH–psbA primer pair
and subjected to DNA sequencing, followed by alignment analysis and dendrogram construction.
Arogya and MKD did not show any antibacterial activity (DZI = 0.0 mm), whereas Sisila, BAN
and MT showed antibacterial activity only against E. coli and S. aureus (mean DZI of 8.2 mm
and 8.4 mm respectively). Bibila sweet and sour orange showed significantly higher antibacterial
activity against all E. coli, S. aureus and methicillin-resistant S. aureus (mean DZI of 10.2 mm,
10.5 mm and 7.8 mm respectively). DNA barcoding provided unique sequence identifiers for each
cultivar. These antibacterial activity data in combination with DNA barcodes could help to develop
new cultivars through breeding to promote the sweet orange industry in Sri Lanka.
