Jingxue Wang

Application of the VPp1 bacteriophage combined with a coupled enzyme system in the rapid detection of Vibrio parahaemolyticus

For rapid and quantitative detection of Vibrio parahaemolyticus, a method combining the specific lysis of bacteriophages with a bacterial luciferase-flavin mononucleotide:nicotinamide adenine dinucleotide oxidoreductase bioluminescent system in vitro was developed. A V. parahaemolyticus detection system was established by optimizing three main influencing factors: bacteriophage titer, volume ratio of the bacteriophage to its host bacterium, and lysis time. A standard curve between the number of bacteria and the luminescence intensity of the coupled enzyme system was studied and revealed a good linear relationship. More than 10(7)colony-forming units (cfu)·ml(-1) bacteria in pure culture and >10(8) cfu·ml(-1) bacteria in oyster samples were readily detected without pre-enrichment. Furthermore, >10(0) cfu·ml(-1) bacteria in oyster samples were readily detected after 4h of enrichment culture. Because of its rapid detection, high specificity, and simplicity in operation, this method is an effective tool for detecting living bacteria in food and environmental samples.

Effects of bacteriophage on the quality and shelf life of Paralichthys olivaceus during chilled storage.

BACKGROUND The microbiological spoilage of fishery foods is mainly due to specific spoilage organisms (SSOs), with Shewanella putrefaciens being the SSO of most chilled marine fish. Bacteriophages have shown excellent capability to control micro-organisms. The aim of this study was to determine a specific bacteriophage to prevent spoilage by reducing SSO (S. putrefaciens) levels in the marine fish Paralichthys olivaceus (olive flounder) under chilled storage. RESULTS Chilled flounder fillets were inoculated with S. putrefaciens and treated with different concentrations of bacteriophage Spp001 ranging from 10(4) to 10(8) plaque-forming units (pfu) mL(-1) . Bacterial growth (including total viable count and SSO) of the bacteriophage-treated groups was significantly inhibited compared with that of the negative control group (P < 0.05). Sensory evaluation and biochemical parameters revealed that the bacteriophage could extend the shelf life of chilled flounder fillets (from <4 to 14 days) with good esthetic quality, even at low temperature (4 °C). Furthermore, bacteriophage concentrations of 10(6) and 10(8) pfu mL(-1) were more effective than the chemical preservative potassium sorbate (5 g L(-1) ). CONCLUSION The bacteriophage Spp001 offered effective biocontrol of S. putrefaciens under chilled conditions, retaining the quality characteristics of spiked fish fillets, and thus could be a potential candidate for use in chilled fish fillet biopreservation.

Quantification of ethanol using a luminescence system derived from Photobacterium leiognathi

We established a method based on a luminescence system driven by NADH conversion to quantitatively detect ethanol in alcoholic beverages. NADH produced by an ADH-catalyzed enzymatic reaction was used as an indicator to directly quantify luminescence in vitro. A strong linear relationship (R2 = 0.9942) was observed between the luminescence intensity and ethanol concentration over a range of 0.002–0.1 mol L−1, providing a detection limit of 1.43 × 10−4 mol L−1 for ethanol. This system has advantages such as rapid detection, high specificity, and repeatability in operation; therefore, it could be an advantageous alternative method for accurate quantification of ethanol content in beer, and may be suitable for other applications in the food industry.

Testing a Nonpathogenic Surrogate Microorganism for Validating Desiccation-Adapted Salmonella Inactivation in Physically Heat-Treated Broiler Litter

Thermal resistance of desiccation-adapted Salmonella Senftenberg 775W was compared with that of Enterococcus faecium NRRL B-2354 in aged broiler litter. Aged broiler litter with 20, 30, and 40% moisture contents was inoculated separately with desiccation-adapted Salmonella Senftenberg 775W and E. faecium NRRL B-2354 at ca. 5 to 6 log CFU/g and then heat treated at 75, 85, and 150°C. At all tested temperatures, desiccation-adapted E. faecium NRRL B-2354 was more heat resistant than desiccation-adapted Salmonella Senftenberg 775W ( P < 0.05). During the treatments at 75 and 85°C, E. faecium NRRL B-2354 in aged broiler litter with all moisture contents was reduced by 2.89 to 4.12 log and was above the detection limit of direct plating (1.30 log CFU/g), whereas Salmonella Senftenberg 775W could not be detected by enrichment (>5-log reduction) during holding time at these temperatures. At 150°C, E. faecium NRRL B-2354 in aged broiler litter with 20 and 30% moisture contents was still detectable by enrichment after heat exposure for up to 15 min, whereas Salmonella Senftenberg 775W in aged broiler litter with all moisture contents could not be detected throughout the entire treatment. Our results revealed that E. faecium NRRL B-2354 can be used as a surrogate for Salmonella to validate the thermal processing of poultry litter by providing a sufficient safety margin. This study provides a practical tool for poultry litter processors to evaluate the effectiveness of their thermal processing.