Screening of bacteria isolates from earthworm cast for antibacterial activities

Abstract

The healthy operation of the soil ecosystem is significantly influenced by earthworms. Various medical treatments have included the use of earthworms. This study isolated and screened bacterial species from earthworm cast for antibacterial activities. Two (2) bacteria species were isolated from the earthworm cast by culturing on starch casein agar using pour plate techniques. The isolates were identified as Streptomyces and Actinomadura species while the test isolates include Klebsiella specie, Salmonella shigella and Staphylococcus aureus strains. This study revealed that Streptococcus and Actinomadura metabolite exhibited variable degrees of antimicrobial activities against the test isolates. The highest in-vitro antimicrobial activity is (12.0mm) was exhibited by the Streptococcus metabolite at the highest concentration of 100mg/ml against Staphylococcus aureus, while the least antimicrobial activity (8.0mm) was exhibited at the concentration of 80mg/ml and 40mg/ml against Salmonella species and Staphylococcus aureus. Actinomadura metabolite was effective against Staphylococcus aureus at the highest concentration of 100mg/ml. However there was significant difference observed in antibacterial activity of the metabolites when compared to the standard antibiotic (Gentamicin) (p<0.05). From the minimum inhibitory concentration (MIC) test result, Streptococcus metabolite demonstrated greater activity on Salmonella specie at the range of 3.12mg/ml and a lower activity on Staphylococcus aureus and Klebsiella specie at the range of 12.5mg/ml each. The Actinomadura metabolite demonstrated greater activity on Salmonella species at the range of 1.56mg/ml. Based on the findings of this research, earthworm (Pheretima posthuma) is a good source of antibacterial agents that can be identified and extracted as source of cheap medicines to control serious infections.