Abstract
Background: Members of the family Flavobacteriaceae exhibit intrinsic multi-drug resistance, which hampers their effective eradication. Phytochemicals are being explored as alternatives to the use of antimicrobial agents in aquaculture since they have growth-promoting, immunestimulating, and antimicrobial properties.Materials and Methods: The susceptibility of 36 Chryseobacterium and seven Myroides spp. isolates from salmon, tilapia and trout as well as 19 selected Flavobacteriaceae type strains to cinnamaldehyde, vanillin and four crude Kigelia africana extracts (ethyl acetate, dichloromethane, methanol and hexane), was assessed using disc diffusion assays and compared to standard antimicrobial agents, ampicillin and tetracycline using activity indices.Results: Cinnamaldehyde (≥250 μg/ml) was the most effective (77. 8 – 100% susceptibility) while vanillin was the least effective with inhibitory activity only at 1000 μg/ml. The K. africana hexane extract (4 mg/ml) was the most effective, with only 11.3% of isolates displaying resistance, while 94.4% of isolates demonstrated resistance to ampicillin and 38.9% susceptibility to tetracycline. K. africana extract inhibitory efficacy decreased in the following order: hexane > ethyl acetate > dichloromethane > methanol. Cinnamaldehyde and K. africana EX 4 activity indices ≥ 1 were obtained for 83.3 - 97.2% and 25% of Chryseobacterium spp. isolates, respectively, relative to tetracycline.Conclusions: Cinnamaldehyde and K. africana fruit hexane extracts are promising candidates to be tested for their efficacy in the treatment of Chryseobacterium/Myroides-associated fish infections. These phytochemicals might serve as environmentally-friendly, cost-effective alternatives to the use of antimicrobial agents in aquaculture farms, with a lesser chance of resistance development.Keywords: phytotherapy; cinnamaldehyde; vanillin; Kigelia; Chryseobacterium; Myroides
Highlights
Intensive aquaculture activities often lead to an increased incidence of infectious diseases resulting in severe economic loss.Antimicrobial agents are used by almost every sector of the aquaculture industry, prophylactically as feed additives to prevent fish disease, in addition to their therapeutic use (Chakraborty and Hancz, 2011)
Cinnamaldehyde and K. africana fruit hexane extracts are promising candidates to be tested for their efficacy in the treatment of Chryseobacterium/Myroides-associated fish infections
Zone diameters for cinnamaldehyde (250 and 1000 μg/ml), vanillin (250 and 1000 μg/ml) and four K. africana extracts (4 mg/ml) are given in Table 1, along with zone diameters for ampicillin and tetracycline
Summary
Antimicrobial agents are used by almost every sector of the aquaculture industry, prophylactically as feed additives to prevent fish disease, in addition to their therapeutic use (Chakraborty and Hancz, 2011). There has been an increase in the frequency of fish clinically presented infections associated with the genus Chryseobacterium (yellow-pigmented, non-fermentative Gram-negative bacilli), with an increasing number of Chryseobacterium species being considered potentially emerging pathogens in farmed Atlantic salmon, rainbow trout and yellow perch (Illardi et al, 2009; Pridgeon et al, 2012; Zamora et al, 2012). Chryseobacterium indologenes, which is normally associated with human infections, acting as sporadic but severe opportunistic nosocomial pathogen usually in neonates or immuno-compromised patients, has been found to be pathogenic to yellow perch (Pridgeon et al, 2012). Phytochemicals are being explored as alternatives to the use of antimicrobial agents in aquaculture since they have growth-promoting, immunestimulating, and antimicrobial properties
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