Screening Of Bacteria Isolated From Earthworm Cast For Antibacterial Activities

RESULTS

3.1. DISCUSSION

This study was focused on earthworm castings because earthworms redistributes organic matter within the soil, increase soil permeability and increase microbial activity by their burrowing and feeding activities (Syers & Springett, 2005). Hence, an effort had been made to explore the bacteria from earthworm castings for their antagonistic activity.

A total of 12 bacteria species were isolated from earthworm casting, out of which 7 (58.33%) were isolated from sample A (grass land in the university of Nigeria, Nsukka) and 5 (41.67%) from sample B (agricultural land in Odenigbo). The isolates were gotten from only nutrient agar, there was no growth on the MacConkey agar (Table 1).

The morphological characterization of the bacterial isolates was done by Gram staining which revealed that all 12 bacterial isolates were gram positive (Table 2). Amongst them the different gram-positive bacteria like bacilli, clustered bacilli, and cocci were observed. Seven cocci and four rod species were observed, one isolate was unidentified.

The bacterial isolates were identified by their biochemical reactions (Table 3) and with the help of Bergey’s manual. The predominant genera were bacilli (33.3%, n=4) followed by staphylococcus (25%, n=3), micrococcus (16.6%, n=2) then enterococcus (8.3%, n=1) and streptococcus (8.3%, n=1).

The antibacterial activity varied among the isolates, among the 12 isolates, four (4) had antagonistic characteristics, two (2) out of the four (4) had antibacterial activity on more than one test organism. During the study it was recorded that the bacilli genera was dominant and the only specie that displayed antagonistic behavior among the earthworm casts isolates (Table 4). Three isolates were able to show significant zone of inhibition (Table 5). Zone of inhibition was measured in millimeters (mm).

Table 1: Details of sampling site and isolation of bacteria from earthworm castings.

Table 2: Gram staining results of the bacterial isolates

Table 3: biochemical characterization and identification of bacteria isolate from earthworm casts

Table 4: Antagonistic activity of isolated bacteria from earthworm casts against test organisms

Table 5: antibacterial activity of isolated bacteria showing significant zone of inhibition