New perspectives for surveying and improving Thai dried seafood qualities using antimicrobials produced by Bacillus velezensis BUU004 against foodborne pathogens

Abstract

Dried seafood products are one of the most popular seafood items in Thailand. This study was divided into two experiments. In first experiment, a survey in intrinsic and bacteriological characteristics of twenty dried seafood products distributed in Chon Buri province, Thailand was performed. Values of water activity, pH and NaCl content were 0.35 ± 0.01-0.72 ± 0.00, 5.47 ± 0.03-9.24 ± 0.01, and 0.66 ± 0.06-2.26 ± 0.03%, respectively. Based on the Thai regulatory standard, half of dried seafood products contained total viable count over acceptable level. Predominant isolated bacteria in dried seafood products were Staphylococcus spp. (39.7%), Bacillus spp. (30.1%), and Pantoea sp. (19.2%). Foodborne pathogens, i.e., B. cereus and Salmonella enterica serovar Weltevreden were found in dried seafood products. In second experiment, two forms of antimicrobials (concentrated (CBV) and partially purified (PBV) substances) prepared from B. velezensis BUU004 and two commercial preservatives (nisin and lactic acid) were introduced into crushed dried seasoned squids to investigate inhibitory activity against pathogens, B. cereus TISTR 687, S. aureus ATCC 25923, Salmonella Typhimurium TISTR 292, and Escherichia coli ATCC 25922. PBV had broader antagonistic activity than CBV, nisin and lactic acid against tested pathogens. Scanning electron microscopy analysis represented bacteriostatic action of PBV on tested pathogens through cell lysis evidenced by an irregular cell shape along with pore formation on cell membranes. Our study demonstrates that PBV has a preservative potential to control pathogen growth and improve biosafety of dried seafood products.

Synergistic antibacterial effects of bacteriocin produced by Bacillus velezensis BUU004 and medicinal plant extracts against Escherichia coli and Salmonella Typhimurium in dried, crushed, and seasoned squid

“…In our recent study, a semi-purified preparation (SPP) containing bacteriocin from Bacillus velezensis BUU004 exhibited broad-spectrum antibacterial activity against food-borne Gram-positive and Gram-negative bacteria (Butkhot et al, 2019a). However, unsatisfactory activity against E. coli and Salmonella Typhimurium was observed when the SPP alone was added to dried seasoned squid.…”

“…A loopful of B. velezensis BUU004 strain was inoculated into TSB, and cultured at 30°C with shaking at 200 rpm for 18 h. Then, the supernatant containing bacteriocin was collected by centrifugation (Centrifuge 5804 R, Eppendorf, Hamburg, Germany) at 8,000 g and 4°C for 10 min. The bacteriocin-containing SPP was prepared by adding ammonium sulphate at 80% saturation to the cell-free supernatant to precipitate proteins with gentle stirring overnight at 4°C (Butkhot et al, 2019a). Subsequently, the precipitated protein was centrifuged at 10,000 g and 4°C for 30 min, and then resuspended in 50 mM sodium phosphate buffer (pH 7.0) prior to dialysis using a dialysis membrane tubing (1 kDa cut-off; Spectrum Laboratory, Los Angeles, CA, USA) at 4°C overnight.…”

“…The SPP was filtered using a 0.45-μm membrane filter (Sartorius, Gottingen, Germany) and stored at -20°C in a sterile amber bottle. The filter-sterilised SPP was assessed for bacteriocin activity in arbitrary units (AUs) as previously described by Butkhot et al (2019a).…”

“…The efficacy of the SPP, the mixed herb extracts, and their combination on S. Typhimurium TISTR 292 and E. coli ATCC 25922 growths in dried seasoned squid was evaluated following the method described by Butkhot et al (2019a). Dried, crushed, and seasoned squid were cut to 2 × 2 cm pieces using sterile scissors.…”

“…In retailed dried seafood products in Thailand, the incidence of viable and pathogenic bacterial counts over the allowable limit has been increasing over the past decade, which reflects the lack of hygiene in the production process (Thungkao and Muangharm, 2008;Nimrat et al, 2019). The most common food-borne pathogenic bacteria in dried seafood products include Bacillus cereus, Escherichia coli, Staphylococcus aureus, and Salmonella (Thungkao and Muangharm, 2008;Butkhot et al, 2019a;Nimrat et al, 2019).…”