In-vitro Antimicrobial Activity of Aeromonas Spp Isolated from Estuary Using Different Screening Protocols

Screening is important in investigating antimicrobial activities of bacteria in a quest to discover new antimicrobials. Various protocols are readily available and employed by researchers worldwide studying microbiostatic and microbicidal activities of bacterial. This research therefore aims at evaluating available protocols and suggesting a standardized model. For the purpose of these research, antimicrobial ability of Aeromonas spp isolated from estuary was investigated using agar well diffusion method, deferred method and agar disc diffusion method respectively. Result obtained reveals that five isolates were positive to antimicrobial production among fifteen bacteria screened. Result was depended on the protocol utilized. Agar well diffusion produced a visible result when compared to others. Next to this was agar disc method. Deferred method involving both cross streaking and spot on lawn could not produce result as of swarming nature of the positive isolates tested. Based on our results, protocols utilized were grouped into preliminary screening test (PST) and confirmatory tests (CT) respectively. Preliminary screening protocol (PST) consists of deferred method – perpendicular cross streaking and spot-on-lawn while confirmatory protocols (CT) are agar well diffusion and agar disc diffusion methods. Preliminary protocols are not enough to conclude existence or non-existence of antimicrobial activity in bacteria. Conclusively, both preliminary and confirmatory protocols should be employed while screening bacteria for antimicrobials as suggested in our model. INTRODUCTION: Increase in global antibiotic resistance of pathogenic bacteria, fungi and protozoa have geared up interest of researchers to investigate different sources for apparent antibiotics discovery. Emerging and re-emerging infections and diseases are continuously posing threat to human existence . For the past decades, marine environment, soil and plants samples have been screened for potential antimicrobial compounds. Bacteria that have been identified as bioactive compounds producers include Pseudomonas, Micrococcus sp , Vibrio ruber 3, 4 Lactobacillus acidophilus 3, , Bifidobacteria , Bacillus , Lactococcus 8, 9, , Staphylococcus, Actinomycetes 11 and Aeromonas hydrophila . Antimicrobials are products of microbial metabolism capable of inhibiting the growth of microorganisms. Antimicrobials have been reported in both Gram positive and negative bacteria . Microbial inhibitory metabolites are either categorized as primary or secondary by-products . According to Nanjwade et al., 2010 , over 10,000