Development of alternatives to synthetic antibiotics against important veterinary pathogens using native herbal plant of Bangladesh

Antibiotic resistance has been recognized globally as one of the major health challenges for this modern era. Accordingly, the search for safe and effective antimicrobial agents has become a top priority for the biomedical field in recent years. Therefore, present study was undertaken to investigate the antimicrobial properties of herbal extract (guava) against bacterial pathogens of veterinary importance in in vitro conditions and thus to propose an alternative herbal candidate to synthetic antibiotics.Qualitative phytochemical analysis of guava leaves was performed to identify the bioactive chemical constituents like tannins, alkaloids, saponins, flavonoids, etc. Plant extracts were prepared using two readily available solvents namely aqua and ethanol. Guava leaves extracts were evaluated against both gram-positive (Staphylococcus aureus) and gram-negative (Escherichia coli) bacteria of veterinary importance that commonly cause diseases in animals and birds. The efficacy of these extracts was tested against the study organisms through a well-diffusion method employing 50mg leaf-extract solution per well. Bacterial growth inhibitory characteristics of the extracts were also investigated by determining the Minimum Inhibitory Concentration (MIC) of the extracts in Nutrient broth. Guava leaves are found to contain different phytochemicals like tannins, phenols, flavonoids, terpenoids, glycosides and saponins which have known antibacterial activity. Antibacterial assay of both the aqueous and ethanol extracts of guava leaves showed inhibitory activity against both gram-positive and gram-negative bacteria. The ethanol extract had better antibacterial activity than aqueous extracts with mean zones of inhibition of 11.8 ± 0.60 mm and 9.5 ± 0.95 mm against Staphylococcus aureus and Escherichia coli, respectively. MIC values revealed that a very low concentration of 6.25 -12.5mg/ml of the extracts inhibit the growth of the tested isolates.  The finding revealed that guava leave extract has great potential as an antimicrobial compound against pathogenic microorganisms of veterinary importance. Guava leaf-extract might be a good candidate in the search for a natural antimicrobial agent. This study provides scientific understanding to further determine the antimicrobial values and investigate other pharmacological properties of such valuable herbal plant.