Antibacterial activity of microalgae and medicinal plants against common bacteria causing diseases in fish, shellfish, canine and poultry

Rapid growth of antimicrobial resistance is a major threat to human and animal health, and development of new drugs with effective microbicidal properties are in demand to the scientific communities. Cyanobacteria and medicinal plants inherit antimicrobial, antioxidant, anti-cancerous and anti-inflammatory properties. In the current research, we investigated antibacterial potential of crude ethanolic extracts from marine microalgae (Chlorella sp. and Spirulina sp.) and medicinal plants (Aloe vera and Clinacanthus nutans) against pathogenic bacteria isolated from chicken, dog, fish, and shellfish. Bacteria including Salmonella sp., Aeromonas sp. and E. coli, Vibrio sp. Streptococcus sp. and Staphylococcus sp., were isolated through colony morphology, Gram staining and VITEK-2 tests. Antibacterial activity was determined by disc diffusion assay. Spirulina sp. showed the highest inhibition zone of 19.3 +/- 0.58 mm against Vibrio sp. compared to other treatments, whereas Chlorella sp. exhibited maximum inhibition zone of 11.41 +/- 0.65 mm against Staphylococcus sp., C. nutans had antibacterial activity against Staphylococcus sp. and E. coli with the maximum zone of inhibition (14.21 +/- 1.08 and 15.10 +/- 0.21 mm), whereas Aloe vera against E. coli and Vibrio sp. with significant inhibition zone of 14.04 +/- 0.90 and 15.36 +/- 1.11mm, respectively. Minimum inhibitory concentration (MIC) of Chlorella sp. was found to be 20 mg/mL against all the test bacteria. Spirulina sp., Aloe vera, and C. nutans had MIC values ranging from 20-40 mg/mL. These findings highlight the antibacterial potential of native microalgae and medicinal plants against virulent bacteria that poses significant threats in poultry, canine and aquaculture.