Abstract
BackgroundIndonesia is the third largest producer of fish and other aquaculture products in the world, making this industry a major contributor in the economy of Indonesia. However, this industry continually overcome challenges, one of them are bacterial outbreaks. In addition, the emergence of these bacterial outbreaks were worsen due to the biofilm produced by many significant pathogenic bacteria and the impact of increased antibiotic resistance. These issues have become a global concern, because antibiotics are currently one of the main treatments available to overcome this problems. Therefore, studies aimed at finding and characterizing bioactive compounds to combat these issues. In this study actinomycetes isolates were screened and characterized for their bioactive compounds produced which have inhibitory and destructive activity and also QS inhibitors against biofilm structure of aquatic pathogenic bacteria, such as Vibrio harveyi, A. hydrophila, and S. agalactiae.ResultExtracts (20 mg/mL) produced by sixteen Actinomycetes isolates showed anti-quorum sensing activity towards reporter stain Chromobacterium violaceum wild-type. Most of these extracts showed better inhibitory activity on all of the pathogenic bacteria biofilm structure tested than the destructive activity on the preformed of those biofilm structure. Subsequently, we also performed characterization of bioactive compound and found that in this study, polysaccharide is the most common antibiofilm agents, which were responsible to their antibiofilm activity. Finally, we found that the value of LC50 of all extracts tested were more than 1 mg/mL, thereby all of extracts tested did not show cyto-toxic effect against Artemia salina.ConclusionAll of the extracts of Actinomycetes isolates showed promising inhibitory activity towards biofilm structure of pathogenic bacteria tested. So far, all of the extracts are potential to be QS inhibitors and antibiofilm agents of all pathogenic bacteria tested.
Highlights
Indonesia is the third largest producer of fish and other aquaculture products in the world, making this industry a major contributor in the economy of Indonesia
We found that several Actinomycetes isolates showed anti-bacterial activity, such as SW17 and CW01 against V. harveyi and S. agalactiae, respectively
The degradation of extracellular polymeric substances (EPS) causes the maturation process on biofilm to be disrupted increasing the sensitivity of the sessile cells to antibiotics and host immune system [21]. Another antibiofilm agent which found in this study was extracellular DNA. This activity was reported by study conducted by [22], which stated that eDNA secreted by Caulobacter crescentus showed an ability to act as anti-adhesive agent by coating the adhesive surface, thereby inhibiting the initial cell attachment which is required for biofilm formation
Summary
Bacterial cultivation Sixteen isolates of Actinomycetes recovered from marine environments from our previous study were cultivated in yeast malt extract agar (YMEA) + 1% calcium carbonate. Screening of anti-quorum sensing activity All of the isolates showed anti-quorum sensing activity against indicator bacteria, namely Chromobacterium violaceum wild-type It is characterized by the translucent zone around the straight streak area of the isolate (Fig. 1) (Table 1). Based on the result there were several isolates, which showed antibacterial activity, such as SW17 and 15, 14, CW01, 16, 18, and 20 against V. harveyi and S. agalactiae, respectively (Fig. 2) (Table 1) These isolates were ruled out in further assay. Brine shrimp lethality assay Seven potential Actinomycetes isolates extracts which showed the highest antibiofilm activity was tested using BSLA method. This assay was performed in five replicates and two different batches.
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