Depuration of Oysters (Crassostrea gigas) Contaminated with Vibrio parahaemolyticus and Vibrio vulnificus with UV Light and Chlorinated Seawater

The efficacy of depuration using UV light and chlorinated seawater for decontaminating Vibrio parahaemolyticus and Vibrio vulnificus from oysters was investigated. Oysters were contaminated with a five-strain cocktail of V. parahaemolyticus or V. vulnificus to levels of 10(4) to 10(5) CFU ml(-1) for bioaccumulation. The depuration was conducted in a closed system in which 350 liters of seawater was recirculated at a rate of 7 liters/min for 48 h at room temperature. Counts of V. parahaemolyticus or V. vulnificus were determined at 0, 6, 18, 24, and 48 h. Three treatments were conducted: T1, control treatment; T2, UV treatment; and T3, UV plus chlorine treatment. After 48 h of depuration of V. parahaemolyticus, T3 reduced the count by 3.1 log most probable number (MPN) g(-1) and T2 reduced the count by 2.4 log MPN g(-1), while T1 reduced the count by only 2.0 log MPN g(-1). After 48 h of depuration of V. vulnificus, T2 and T3 were efficient, reducing the counts by 2.5 and 2.4 log MPN g(-1), respectively, while T1 reduced the count by only 1.4 log MPN g(-1). The UV light plus chlorine treatment was more efficient for controlling V. parahaemolyticus in oysters. Both UV light and UV light plus chlorine were efficient for V. vulnificus. The present study is the first report showing the efficacy of depuration systems for decontaminating V. parahaemolyticus and V. vulnificus in oysters cultivated on the Brazilian coast. This study provides information on processes that can contribute to controlling and preventing such microorganisms in oysters and could be used for effective postharvest treatment by restaurants and small producers of oysters on the coast of Brazil.     

Growth and Survival Differences of Vibrio vulnificus and Vibrio parahaemolyticus Strains during Cold Storage

ABSTRACT:  Vibrio vulnificus  and  Vibrio parahaemolyticus  are the most common  Vibrio  species associated with seafood illness in the United States. Our study was conducted to determine if strain-to-strain differences exist in the growth and survival of 8 different  V. vulnificus  and  V. parahaemolyticus  strains at low temperatures. By day 10,  V. vulnificus  strain 515-4C2 had significantly higher counts ( P  < 0.05) (1.97 log CFU/g) compared with strains 3315, 1007, 29306 at 5 °C, which reached nondetectable levels. At 8 °C, strain 515-4C2 had significantly higher counts ( P  < 0.05) (2.23 log CFU/mL) compared with 1007, 33815, 541(O) 49C, which reached nondetectable levels. At 10 °C, only  V. vulnificus  strain 33815 reached nondetectable levels. At 5 °C,  V. parahaemolyticus  strain 541(O) 57C had the highest counts (5.28 log CFU/g) by day 10 while strain 33847 had significantly lower counts (3.46 log CFU/g). After 10 d at 8 °C,  V. parahaemolyticus  strain M350A had the highest counts (7.97 log CFU/mL) while strain 541(O) 57C had the lowest counts (4.80 log CFU/mL). At 10 °C,  V. parahaemolyticus  strain NY477 had significantly higher counts ( P  < 0.05) with 8.31 log CFU/mL compared with strain 33847, which had the lowest counts (6.77 log CFU/mL). Our research has shown that various  V. vulnificus  and  V. parahaemolyticus  strains vary in their ability to survive and grow at refrigeration temperatures.     

Effects of electrolyzed oxidizing water treatment on reducing Vibrio parahaemolyticus and Vibrio vulnificus in raw oysters

Contamination of Vibrio parahaemolyticus and Vibrio vulnificus in oysters is a food safety concern. This study investigated effects of electrolyzed oxidizing (EO) water treatment on reducing V. parahaemolyticus and V. vulnificus in laboratory-contaminated oysters. EO water exhibited strong antibacterial activity against V. parahaemolyticus and V. vulnificus in pure cultures. Populations of V. parahaemolyticus (8.74 x 10(7) CFU/ml) and V. vulnificus (8.69 x 10(7) CFU/ml) decreased quickly in EO water containing 0.5% NaCl to nondetectable levels (> 6.6 log reductions) within 15 s. Freshly harvested Pacific oysters were inoculated with a five-strain cocktail of V. parahaemolyticus or V. vulnificus at levels of 10(4) and 10(6) most probable number (MPN)/g and treated with EO water (chlorine, 30 ppm; pH 2.82; oxidation-reduction potential, 1131 mV) containing 1% NaCl at room temperature. Reductions of V. parahaemolyticus and V. vulnificus in oysters were determined at 0 (before treatment), 2, 4, 6, and 8 h of treatment. Holding oysters inoculated with V. parahaemolyticus or V. vulnificus in the EO water containing 1% NaCl for 4 to 6 h resulted in significant (P < 0.05) reductions of V. parahaemolyticus and V. vulnificus by 1.13 and 1.05 log MPN/g, respectively. Extended exposure (> 12 h) of oysters in EO water containing high levels of chlorine (> 30 ppm) was found to be detrimental to oysters. EO water could be used as a postharvest treatment to reduce Vibrio contamination in oysters. However, treatment should be limited to 4 to 6 h to avoid death of oysters. Further studies are needed to determine effects of EO water treatment on sensory characteristics of oysters.     

Reductions of Vibrio parahaemolyticus in Pacific oysters (Crassostrea gigas) by depuration at various temperatures

Consumption of raw oysters has been linked to several outbreaks of Vibrio parahaemolyticus infection in the United States. This study investigated effects of ice storage and UV-sterilized seawater depuration at various temperatures on reducing V. parahaemolyticus in oysters. Raw Pacific oysters (Crassostrea gigas) were inoculated with a mixed culture of five clinical strains of V. parahaemolyticus (10290, 10292, 10293, BE 98-2029 and 027-1c1) at levels of 10⁴⁻⁶ MPN/g. Inoculated oysters were either stored in ice or depurated in recirculating artificial seawater at 2, 3, 7, 10, 12.5, and 15 °C for 4–6 days. Holding oysters in ice or depuration of oysters in recirculating seawater at 2 or 3 °C for 4 days did not result in significant reductions (P > 0.05) of V. parahaemolyticus in the oysters. However, depuration at temperatures between 7 and 15 °C reduced V. parahaemolyticus populations in oysters by >3.0 log MPN/g after 5 days with no loss of oysters. Depuration at refrigerated temperatures (7–15 °C) can be applied as a post-harvest treatment for reducing V. parahaemolyticus in Pacific oysters.     

Low temperature pasteurization to reduce the risk of vibrio infections from raw shell-stock oysters

Vibrio vulnificus and V. parahaemolyticus are natural inhabitants of estuarine environments and may be transmitted to humans by ingestion of raw oysters. This study focused on the use of low temperature pasteurization, to reduce these Vibrio spp. to nondetectable levels, thus reducing the risk of infection associated with raw oyster consumption. Artificially inoculated V. vulnificus and V. parahaemolyticus and naturally-contaminated V. vulnificus in live oysters were pasteurized at 50%deg;C for up to 15min. Samples of processed and unprocessed oysters were enumerated for V. vulnificus, V. parahaemolyticus, and aerobic spoilage bacteria for 0-14 days. Low temperature pasteurization was effective in reducing these pathogens from > 100000 to non-detectable levels in less than 10min of processing. Spoilage bacteria were reduced by 2-3 logs, thus increasing the shelf-life for up to 7 days beyond live unprocessed oysters. Vibrio vulnificus in control oysters was reduced by 102 during ice storage alone. Following pasteurization and during a temperature storage abuse study (24h at 22°C), V. vulnificus was not recovered. During this storage period spoilage bacteria exceeded 1 million/g oyster meat.     

Bactericidal effects of wine on Vibrio parahaemolyticus in oysters

The bactericidal effects of wines on Vibrio parahaemolyticus in oysters were studied to evaluate potential inactivation of V. parahaemolyticus in contaminated oysters by wine consumption. Shucked whole oyster and oyster meat homogenate were inoculated with V. parahaemolyticus and mixed with red or white wine. Survivals of V. parahaemolyticus in inoculated oysters were determined at 7 and 25 degrees C. Populations of V. parahaemolyticus in inoculated whole oysters (5.52 log most probable number [MPN] per g) decreased slightly to 4.90 log MPN/g (a 0.62-log reduction) after 24 h at 7 degrees C but increased to 7.37 log MPN/g over the same period at 25 degrees C. However, the populations in wine-treated whole oysters decreased by >1.7 and >1.9 log MPN/g after 24 h at 7 and 25 degrees C, respectively. Both red and white wines were more effective in inactivating V. parahaemolyticus in oyster meat homogenate than in whole oyster. Populations of V. parahaemolyticus in oyster meat homogenate (7.8 x 10(3) MPN/g) decreased rapidly to nondetectable levels (< 3 MPN/g) after 30 min of mixing with wine at 25 degrees C (a 3.89-log MPN/g reduction). These results suggest that chewing oysters before swallowing when eating raw oysters may result in greater inactivation of V. parahaemolyticus if wine is consumed. More studies are needed to determine the bactericidal effects of wine on V. parahaemolyticus in the complicated stomach environment.     

Vibrio vulnificus and Vibrio parahaemolyticus in U.S. retail shell oysters: a national survey from June 1998 to July 1999.

From June 1998 to July 1999, 370 lots of oysters in the shell were sampled at 275 different establishments (71%, restaurants or oyster bars; 27%, retail seafood markets: and 2%, wholesale seafood markets) in coastal and inland markets throughout the United States. The oysters were harvested from the Gulf (49%). Pacific (14%), Mid-Atlantic (18%), and North Atlantic (11%) Coasts of the United States and from Canada (8%). Densities of Vibrio vulnificus and Vibrio parahaemolyticus were determined using a modification of the most probable number (MPN) techniques described in the Food and Drug Administration's Bacteriological Analytical Manual. DNA probes and enzyme immunoassay were used to identify suspect isolates and to determine the presence of the thermostable direct hemolysin gene associated with pathogenicity of V. parahaemolyticus. Densities of both V. vulnifcus and V. parahaemolyticus in market oysters from all harvest regions followed a seasonal distribution, with highest densities in the summer. Highest densities of both organisms were observed in oysters harvested from the Gulf Coast, where densities often exceeded 10,000 MPN/g. The majority (78%) of lots harvested in the North Atlantic, Pacific, and Canadian Coasts had V. vulnificus densities below the detectable level of 0.2 MPN/g; none exceeded 100 MPN/g. V. parahaemolyticus densities were greater than those of V. vulnificus in lots from these same areas, with some lots exceeding 1,000 MPN/g for V. parahaemolyticus. Some lots from the Mid-Atlantic states exceeded 10,000 MPN/g for both V. vulnificus and V. parahaemolyicus. Overall, there was a significant correlation between V. vulificus and V. parahaemolyticus densities (r = 0.72, n = 202, P < 0.0001), but neither density correlated with salinity. Storage time significantly affected the V. vulnificus (10% decrease per day) and V. parahaemolyticus (7% decrease per day) densities in market oysters. The thermostable direct hemolysin gene associated with V parahaemolyticus virulence was detected in 9 of 3,429 (0.3%) V. parahaemolyticus cultures and in 8 of 198 (4.0%) lots of oysters. These data can be used to estimate the exposure of raw oyster consumers to V. vulnificus and V. parahaemolyticus.     

Occurrence of Vibrio parahaemolyticus in Two Oregon Oyster-growing Bays

ABSTRACT: Occurrence of Vibrio parahaemolyticus in 2 Oregon oyster-growing areas (Yaquina andTillamook Bays) was studied from November 2002 to October 2003. Vibrio parahaemolyticus was detected in 15.0% of oyster, 20.0% of seawater, and 47.5% of sediment samples with very low levels of pathogenic strains being detected in oysters (≤3.6 most probable number [MPN] /g). The densities of total and pathogenic V. parahaemolyticus were higher in sediment (≤1100 and ≤43 MPN/g) than in seawater (≤15 and ≤3.6 MPN/100 mL) or oyster (≤43 and ≤3.6 MPN/ g). Densities of V. parahaemolyticus in both bays were positively correlated to water temperatures ( P < 0.01), with higher densities in samples being detected in summer, especially July and August. There was no correlation between the densities of V. parahaemolyticus and water salinity or the densities of V. parahaemolyticus and bacterial populations in seawater. Freshly harvested oysters should be kept at refrigeration temperatures to prevent rapid growth of pathogenic V. parahaemolyticus in contaminated oysters.     

温暖月份零售带壳牡蛎中副溶血性弧菌的定量研究

为了解温暖月份零售带壳牡蛎中副溶血性弧菌 (VP)的污染情况 ,2 0 0 3年 4～ 8月在福建省福州和厦门两地共收集带壳牡蛎 113份 ,样品分别来自水产品批发市场 (18% ) ,零售市场 (4 6 % )和饭店 (36 % )。采用Vitek鉴定系统和最可能数法进行VP的定量分析。结果显示 ,带壳牡蛎中VP密度的几何均数为 6 0MPN 10 0g ,4 1 6 %的样品VP密度低于 30MPN 10 0g的最低检出限 ,仅厦门2个样品菌量超过 2 4 0 0 0MPN 10 0g。两个地区、不同采样点和不同月份之间样品VP密度的几何均数差别均有统计学意义 (P <0 0 1)。厦门样品污染菌量高于福州 ;批发市场样品菌量最高 ;5月份样品菌量最高 ,为 14 9MPN 10 0g ,而 6～ 8月样品菌量约为 4 0MPN 10 0g。零售环节带壳牡蛎VP的检出率较高。未来应加强对生食海产品中VP污染状况的监测。     

福建省带壳牡蛎中副溶血性弧菌的市场调查

为了解零售带壳牡蛎中副溶血性弧菌(VP)的污染情况，2003年4月～2004年3月每月在福建省福州和厦门两地收集带壳牡蛎，样品共252份，分别来自水产品批发市场(11％)、零售市场(50％)和饭店(39％)。采用Vitek鉴定系统和最可能数(MPN)法进行VP的定性和定量分析。结果显示，带壳牡蛎VP几何平均密度为46MPN，100g，46％的试样VP密度低于30MPN/100g的最低检出限，仅厦门2个试样菌量超过104MPIN/100g。两个地区、不同采样点和不同季节之间试样vP平均密度差别均有显性。厦门试样菌量高于福州；批发市场试样菌量最高；春季试样菌量(93MPN/100g)高于其它季节(约为40MPN/100g)。研究结果可以用于估计生食牡蛎人群VP的暴露量。     

Inactivation of Vibrio parahaemolyticus and Vibrio vulnificus in oysters by high-hydrostatic pressure and mild heat

Several recent outbreaks associated with oysters have heightened safety concerns of raw shellfish consumptions, with the majority being attributed to Vibrio spp. The objective of this study was to determine the effect of high-hydrostatic pressure (HHP) followed by mild heating on the inactivation of Vibrio parahaemolyticus and Vibrio vulnificus in live oysters. Inoculated oysters were randomly subjected to: a) pressurization at 200–300 MPa for 2 min at 21 °C, b) mild heat treatment at 40, 45 or 50 °C for up to 20 min and c) pressure treatment of 200–300 MPa for 2 min at 21 °C followed by heat treatment at 40–50 °C. Counts of V. parahaemolyticus and V. vulnificus were then determined using the most probable number (MPN) method. Pressurization at 200–300 MPa for 2 min resulted in various degrees of inactivation, from 1.2 to >7 log MPN/g reductions. Heat treatment at 40 and 45 °C for 20 min only reduced V. parahaemolyticus and V. vulnificus by 0.7–2.5 log MPN/g while at 50 °C for 15 min achieved >7 log MPN/g reduction. HHP and mild heat had synergistic effects. Combinations such as HHP at 250 MPa for 2 min followed by heat treatment at 45 °C for 15 min and HHP at 200 MPa for 2 min followed by heat treatment at 50 °C for 5 min reduced both V. parahaemolyticus and V. vulnificus to non-detectable levels by the MPN method (<3 MPN/g). HHP at ≥275 MPa for 2 min followed by heat treatment at 45 °C for 20 min and HHP at ≥200 MPa for 2 min followed by heat treatment at 50 °C for 15 min completely eliminated both pathogens in oysters (negative enrichment results). This study demonstrated the efficiency of HHP followed by mild heat treatments on inactivation of V. parahaemolyticus and V. vulnificus and could help the industry to establish parameters for processing oysters.     

Comparison of a Chromogenic Medium with Thiosulfate-Citrate-Bile Salts-Sucrose Agar for Detecting Vibrio parahaemolyticus

ABSTRACT: The widely used most probable number (MPN) method for detecting Vibrio parahaemolyticus cannot differentiate growth of V. parahaemolyticus from Vibrio vulnificus or Vibrio mimicus on the thiosulfate-citrate-bile salts-sucrose agar (TCBS). Presumptive positive colonies grown onTCBS need to be confirmed with lengthy biochemical tests. This study compared a chromogenic medium, Bio-Chrome Vibrio medium (BCVM), with TCBS for detecting V. parahaemolyticus in seawater, sediment, and oysters using a 3-tube MPN method. Among the 296 samples tested, 136 and 92 samples produced presumptive positive results on TCBS and BCVM, respectively. Biochemical tests and a multiplex polymerase chain reaction (PCR) assay confirmed 74 of 83 samples that were presumptive positive on both TCBS and BVCM as V. parahaemolyticus . Although false-positive results were reported when either medium was used, there were 62 reported for TCBS whereas only 15 were reported for BCVM. The specificities of TCBS and BCVM for V. parahaemolyticus detection were determined to be 77% and 94%, respectively. The accuracies of detecting V. parahaemolyticus were 54% for TCBS and 84% for BCVM. The Bio-Chrome Vibrio medium can be used in the MPN method to reduce the number of biochemical tests needed for V. parahaemolyticus confirmation.     

High salinity relay as a postharvest processing strategy to reduce vibrio vulnificus levels in Chesapeake Bay oysters (Crassostrea virginica)

In 2009 the U.S. Food and Drug Administration (FDA) announced its intention to implement postharvest processing (PHP) methods to eliminate Vibrio vulnificus from oysters intended for the raw, half-shell market that are harvested from the Gulf of Mexico during warmer months. FDA-approved PHP methods can be expensive and may be associated with unfavorable responses from some consumers. A relatively unexplored PHP method that uses relaying to high salinity waters could be an alternative strategy, considering that high salinities appear to negatively affect the survival of V. vulnificus. During relay, however, oysters may be exposed to rapid and large salinity increases that could cause increased mortality. In this study, the effectiveness of high salinity relay to reduce V. vulnificus to <30 most probable number (MPN) per g and the impact on oyster mortality were assessed in the lower Chesapeake Bay. Two relay experiments were performed during the summer and fall of 2010. Oysters collected from three grow-out sites, a low salinity site (14 to 15 practical salinity units [psu]) and two moderate salinity sites (22 to 25 psu), were relayed directly to a high salinity site (≥30 psu) on Virginia's Eastern Shore. Oysters were assayed for V. vulnificus and Vibrio parahaemolyticus (another Vibrio species of concern) densities at time 0 prior to relay and after 7 and 14 days of relay, using the FDA MPN enrichment method combined with detection by real-time PCR. After 14 days, both V. vulnificus and V. parahaemolyticus densities were ≤0.8 MPN/g, and decreases of 2 to 3 log in V. vulnificus densities were observed. Oyster mortalities were low (≤4%) even for oysters from the low salinity harvest site, which experienced a salinity increase of approximately 15 psu. Results, although preliminary and requiring formal validation and economic analysis, suggest that high salinity relay could be an effective PHP method.     

Growth and survival of Vibrio parahaemolyticus in postharvest American oysters

Oysters at the retail stage of distribution generally contain greater densities of Vibrio parahaemolyticus than do oysters at harvest. The objective of this study was to determine the effects of postharvest storage at 26 and 3 degrees C on the growth and survival of naturally occurring V. parahaemolyticus in shellstock American oysters (Crassostrea virginica). Oysters were collected monthly from May 1998 through April 1999 from Mobile Bay, Alabama, and their V. parahaemolyticus densities were determined after 0, 5, 10, and 24 h of postharvest storage at 26 degrees C. After 24 h of storage at 26 degrees C, oysters were transferred to a refrigerator at 3 degrees C and analyzed 14 to 17 days later. V. parahaemolyticus numbers were determined by a direct plating method involving an alkaline-phosphatase-labeled DNA probe that targets the species-specific thermolabile hemolysin gene (tlh-AP) to identify suspect isolates. From April to December, when water temperatures at harvest were >20 degrees C, the geometric mean harvest density of V. parahaemolyticus was 130 CFU/g. When water temperatures were <20 degrees C, the geometric mean harvest density was 15 CFU/g. After harvest, V. parahaemolyticus multiplied rapidly in live oysters held at 26 degrees C, showing a 50-fold increase (1.7 log CFU/g) at 10 h and a 790-fold increase (2.9 log CFU/g) at 24 h (April through December). Average V. parahaemolyticus numbers showed a sixfold decrease (0.8 log CFU/g) after approximately 14 days of refrigeration. These results indicate that V. parahaemolyticus can grow rapidly in unrefrigerated oysters.     

Response of Vibrio parahaemolyticus 03:K6 to a hot water/cold shock pasteurization process.

Vibrio vulnificus and V. parahaemolyticus are natural inhabitants of estuarine environments world wide. Pathogenic strains of these bacteria are often transmitted to humans through consumption of raw oysters, which flourish in the same estuaries. Previous studies reported the effective use of hot water pasteurization followed by cold shock to eliminate from raw oysters naturally and artificially incurred environmental strains of V. vulnificus and V. parahaemolyticus common to the Gulf of Mexico. The present study focused on the use of the same pasteurization method to reduce a highly process resistant Vibrio strain, V. parahaemolyticus O3:K6 to non-detectable levels. Oysters were artificially contaminated with 10(4) and 10(6) V. parahaemolyticus 03:K6 cfu g(-1) oyster meat. Contaminated oysters were pasteurized between 50 and 52 degrees C for up to 22 min. Samples of processed oysters were enumerated for V. parahaemolyticus O3:K6 at 2-min intervals beginning after the 'come-up time' to achieve an oyster internal temperature of at least 50 degrees C. The D value (D(52)deg C) was 1.3-1.6 min. V. parahaemolyticus O3:K6 proved more process resistant than non-pathogenic environmental strains found in Gulf of Mexico waters. A total processing time of at least 22 min at 52 degrees C was recommended to reduce this bacterium to non-detectable levels (< 3 g(-1) oyster meat).     

THE SURVIVAL OF MARINE VIBRIOS IN MERCENARIA MERCENARIA, THE HARDSHELL CLAM

A depuration chamber was used to study the persistence of marine vibrios in the hardshell clam, Mercenaria mercenaria. Specimens of M. mercenaria were incubated for two h in artificial seawater containing 10³ cells/ml each of the following bacterial species; Vibrio parahaemolyticus, Vibrio harveyi and Escherichia coli, and then transferred to the depuration chamber (a tank through which U. V.-sterilized artificial seawater was continually flowing). Numbers of the three bacterial species in tissues of M. mercenaira removed from the chamber at various times were determined by differential plating techniques. The number of each species ranged from 10² to 10³ colony-forming units/gram tissues immediately after transfer to the depuration chamber. After 24 h at 25°C the number of E coli cells detected had decreased over 100-fold. Generally, V. parahaemolyticus and V. harveyi were found in increased abundance after 24 h. The abundance of V. parahaemolyticus and V. harveyi in clams that had been incubated in the depuration chamber for 72 h at 25°C was approximately 10% of the abundance of these species immediately after transfer to the chamber. Similar results were obtained when the incubation temperature was 8 or 15°C and when initial cell concentrations were altered. Thus, V. harveyi and the potential human pathogen, V. parahaemolyticus which are both of marine origin were not removed from M. mercenaria at a rate comparable to the rate at which M. mercenaria depurated cells of E. coli.     

生食动物性水产品中副溶血性弧菌和创伤弧菌污染状况分析

目的 了解生食动物性水产品中副溶血性弧菌和创伤弧菌污染状况。方法 采用随机抽样方法,在我国13个地区的餐饮店、零售店和批发市场采集生食动物性水产品,共计2 980份,对样品进行副溶血性弧菌和创伤弧菌检测。结果 生食动物性水产品中副溶血性弧菌检出率为14.7%(437/2 980),污染水平＞100 MPN/g的样品比例为2.9%(83/2 909);创伤弧菌检出率为3.5%(104/2 980)。采样于批发市场的样品中副溶血性弧菌检出率、污染水平＞100 MPN/g的样品比例和创伤弧菌检出率均高于餐饮店和零售店。第三季度副溶血性弧菌检出率、污染水平＞100 MPN/g的样品比例和创伤弧菌检出率最高。造成污染的主要原因包括原产地污染,储存不当及加工过程交叉污染。结论 生食动物性水产品中存在副溶血性弧菌和创伤弧菌的污染,其健康风险应引起关注,本次污染状况分析可为标准制修订提供理论依据。     

NOVEL NONTHERMAL METHODS TO REDUCE VIBRIO VULNIFICUS IN RAW OYSTERS

Vibrio vulnificus is a foodborne pathogen associated with consumption of raw oyster. No scientific data is available on postharvest treatments of oyster by ultrasound, ozone, and organic acids. This study was designed to investigate the effects of these treatments on inactivation of V. vulnificus naturally present in the in-shell or half-shelled oysters. In in-shell oysters, these treatments were not effective in reducing the number of this pathogen. Half-shelled oysters treated with ultrasound, and ozone in 2% saline for 30 min had 1 and 1.5 log less V. vulnificus, respectively (p<0.05). Treatment of half-shelled oysters by 50 and 100% lemon juice, 5% citric acid, 10% citric acid, or vinegar for 30 min resulted in a significant reduction (2–4 log) in the numbers of V. vulnificus (p<0.05). Although these methods significantly reduced the population of V. vulnificus in raw oysters, they were not able to reduce the numbers of this pathogen to acceptable level (<3 MPN/g).     

Effective reduction of Vibrio vulnificus in the Eastern oyster (Crassostrea virginica) using high salinity depuration

Depuration under different salinities was used to reduce the human pathogen Vibrio vulnificus from Eastern oysters (Crassostrea virginica). Individual recirculating systems were used to test the efficacy of depuration at three salinities (15, 25, and 35 psu) in four independent trials during a 14 day period. Initial loads of V. vulnificus were higher than 10,000 MPN/g of oyster meat in all trials. Data showed that 25 and 35 psu treatments were more efficient in reducing V. vulnificus numbers than 15 psu with an overall reduction of >3 logs. A significant decrease in MPN/g was observed as early as day 6 and further reductions were observed at day 10, while longer depurations did not improve efficacy. Only the highest salinity (35 psu) was capable of reducing V. vulnificus numbers to the FDA recommended level of <30 MPN/g in two of the four trials. Oysters survived well in the depuration systems with minimal mortality (<1%) but their condition index (meat quality and yield) decreased during the 14 day period in all treatments. The data presented in this study suggests that high salinity depuration is a promising method to reduce V. vulnificus in oysters.     

Detection and Enumeration of Vibrio vulnificus by Direct Colony Immunoblot

ABSTRACT:  A direct colony immunoblot method (DCI) for the enumeration of Vibrio vulnificus was developed. Bacterial colonies were transferred from agar plates to membranes, which were then dried and blocked with bovine serum albumin. Subsequently, the membranes were treated with anti- V. vulnificus H antibodies, washed and incubated with peroxidase-conjugated goat anti-rabbit IgG. After a final wash, the membranes were exposed to a substrate mixture containing H₂O₂ which resulted in the development of a purple color by V. vulnificus colonies. The DCI detected all clinical and environmental V. vulnificus strains tested and did not cross-react with other Vibrio species including V. cholerae , V. parahaemolyticus , or V. fluvialis . The DCI was then compared to the DNA hybridization procedure (DNAH) using V. vulnificus agar plates inoculated with mixed cultures of V. vulnificus and V. parahaemolyticus and V. vulnificus -seeded oyster homogenates. Both DCI and DNAH detected 1 to 2 log colony forming units (CFU)/mL V. vulnificus mixed with 4 log CFU/mL V. parahaemolyticus . Both methods were comparable and demonstrated no significant statistical differences when enumerating V. vulnificus in mixed cultures or in oyster homogenates seeded with levels of V. vulnificus from 2 to 6 log CFU/mL. The DCI demonstrated clearer color development and was less time consuming than the DNAH.