Vibriosis in fresh and under-cooked RTE seafood, and how HPP can be a part of the solution to minimize seafood illness risk

 

High pressure processing of seafood is claimed to be one of the best alternatives to prevent pathogens contamination, such as Vibrio spp., while maintaining the sensorial and nutritive properties of food. Recent researches, for instance, Ma & Su (2011) or Serment-Moreno et al. (2015), guarantee its effectiveness in oysters; besides, FAO considers HPP ideal to achieve the food safety and high quality objectives that the consumer demands.


Summer time is great to take a break from everyday routine and travel. Beaches around the world are popular destinations as the warm weather makes it enjoyable for all sort of activities like bathing in seawater, walking around the sand with the sea breeze, sunbathing, and possibly enjoy some tasty, fresh seafood dishes. Nonetheless, the nice summer weather is also enjoyed by microorganisms, providing ideal conditions for pathogen growth in warm seawater, which significantly increases the likelihood of foodborne illness by consuming raw or undercooked seafood.

Crab is a seafood favorite among consumers and there is a wide variety of dishes like steamed claws, crab cakes or wet salads, to name just a few. Unfortunately, the U. S. Food and Drug Administration (FDA) and Center for Disease Control and Prevention (CDC) emitted warnings on July 13 due to potential contamination of imported fresh or precooked crab meat with Vibrio spp.

Authorities strongly advise consumers, restaurants and retailers to avoid RTE crab meat coming from Venezuela (identified source), due to the high risk of developing Vibrio spp. infection, also known as vibriosis. The disease is characterized by diarrhea, vomiting, abdominal cramps, nausea, fever and stomach pain, and symptoms start around 24 hours after consumption. Extra care should be taken for children, elders, and people with ailing chronic disease or weakened immune systems, since vibriosis may have fatal consequences. The most recent CDC update indicates that the outbreak has been traced back to the beginning of April, resulting in 12 infections, where 4 required hospitalization and fortunately no fatalities, so far.

Historic perspective of Vibrio spp. foodborne outbreaks

Vibrio species are Gram-negative and salt-tolerant bacteria able to grow in cold marine environments, where they persist and can be easily found in oysters, clams and fish. Seven of these Vibrio species can cause foodborne infections: V. cholera, V. parahaemolylicus, V. vulnificus, V. mimicus, V. hollisae, V. fluvialis and V. fumissii.

According to the Food and Agriculture Organization of the United Nations (FAO), V. vulnificus and V. parahaemolyticus (Fig. 1) are the most relevant species in seafood poisoning due to their pathogenicity and prevalence (World Health Organization & Food and Agriculture Organization of the United Nations, 2005).

V. vulnificus is an opportunistic pathogen commonly found in bivalves that may induce septicemia (bloodstream infection) whilet V. parahaemolyticus can produce the “thermostable direct hemolysin” (TDH) toxin, capable of damaging erythrocytes cell wall and causing serious gastroenteritis.

Fig. 1. Microscopy images of pathogens Vibrio vulnificus (left) and Vibrio parahaemolyticus (right).

Vibrio spp. is not very common in crab since it is usually consumed cooked. Nonetheless, the ongoing foodborne outbreak is far from being a casual event, since woes related to Vibrio spp. foodborne illness cases due to raw or undercooked seafood consumption are well documented. The Center for Disease Control and Prevention (CDC) voluntarily instated the Cholera and Other Vibrio Illness Surveillance (COVIS) started back in 1988 with Gulf Coast States to monitor seawater conditions to evaluate Vibrio spp. risk, track ongoing outbreaks, and communicate the population.

According to available data in the National Outbreak Reporting System (NORS), Vibrio spp. foodborne incidences peaked in 1998 with 536 confirmed cases (Fig. 2), and all east and west coasts states in the US voluntarily decided to join COVIS. As a result, the number of confirmed Vibrio incidents dramatically decreased below 60 confirmed annual cases (Fig. 2), except for years 2004 and 2006 in which 159 and 300 confirmed cases were reported, respectively, which coincided with very active hurricane seasons.

Fig. 2. Reported foodborne outbreaks associated with Vibrio spp. in the United Sates. Note: bars with multiple colors indicate that other foodborne pathogens (i. e. Listeria monocytogenes) had been associated with the same incident. Data source: foodborne outbreaks reported by the National Outbreak Reporting System (NORS).

Overall, NORS data indicates that 67.4% of reported Vibrio spp. foodborne illness cases could be attributed to the consumption of oysters. As previously shared on our December blog post HPP Seafood: Shells Away with High Pressure Processing, oysters and bivalve shellfish feed by filtering water through themselves, which may result in the accumulation of foodborne pathogens like Vibrio spp. Vibriosis risk is significantly lower for crab, shrimp, and lobster (4-10% of incidences) since most of these aquatic foods are cooked before consumption, but outbreaks may still occur and the three products comprise nearly 22% of total vibriosis cases (Table 1).

Table 1. Vibriosis incidence associated with frequently consumed shellfish in the United States reported from 1998-2016.

Category Food/Ingredient % Illness % Hospitalization
Mollusks Oysters 67.4 4.4
Clams 8.5 5.4
Mussels 1.2 4.8
Scallops 0.1
Crustaceans Crab 8.7 4.0
Shrimp 10.2 0.6
Lobster 4.0 2.9
*1,765 total illness cases. Data source: National Outbreak Reporting System (NORS)

High pressure processing (HPP): a suitable alternative to minimize Vibriosis incidence in seafood

In the United States, the Interstate Shellfish Sanitation Conference (ISSC) established ≥3.52 log10 reductions of Vibrio spp. as the shellfish processing standard, which is likely to be achieved by HPP at relatively mild pressure levels (150-350 MPa; Table 2). In example, processing at 293 MPa for 2 min delivered ≥3.52 log10 reductions of V. parahaemolyticus inoculated in Pacific oysters (Ma & Su, 2011). V. vulinfifcus is less pressure resistant than V.parahaemolyticus, and HPP consistently yields > 5 log10 reductions around 250 MPa. A microbial risk assessment studies suggest that HPP oysters at 250 MPa achieved  ≥3.52 log10 reductions of V. vulnificus, and reduced the probability of septicemia from ~4,900 to less than 4 cases for every 100 million consumption events (Serment-Moreno et al., 2015).

Table 2. Inactivation of Vibrio spp. in bivalve mollusks.

Pathogen Product P (MPa) t (min) T (°C) Log reduction

(cfu ml-1 or cfu g-1)

Reference
Vibrio parahaemolyticus Clam juice 172 10 23 6.0 (Styles et al., 1991)
Oyster 200 10 25 6.0 (Berlin et al., 1999)
300 5 5 6.2 (Phuvasate et al., 2015)
293 8 8 3.5 (Ma & Su, 2011)
300 2 21 6.4 (Ye. et al. 2013)
300 2 21 7.0 (Ye et al., 2012)
300 3 28 5.0 (Cook, 2003)
345 1 22 4.5 (Koo et al., 2006)
350 2 20 5.3 (Kural et al., 2008)
Vibrio vulnificus Oyster 241 2 22 5.4 (Koo et al., 2006)
  250 4 1 5.4 (Kural & Chen., 2006)
  275 2 21 8.3 (Ye. et al. 2013)
  275 2 21 7.4 (Ye et al., 2012)

When compared to other technologies, food-processing experts consulted by the FAO considered HPP provides an ideal balance to achieve food safety objectives, high consumer quality, and convenience for food processors as summarized in Table 3.

In HPP, pressure is generated with water at chilled or room temperature (4-25°C/40-75°F), transmitted instantaneously and uniformly on seafood regardless of size or shape. As seen on Table 2, pressure holding times between 1-2 min may be sufficient to eliminate Vibrio spp., resulting in high throughput (260-3,000 kg/h; 600-6,000 lb/h) with a very low energy consumption. Furthermore, pressure denatures the muscle binding the meat and shell of shellfish, allowing up to 100% meat recovery (No Shuck!) while significantly reducing labor costs required for manual shucking.

Conversely, rapid cooling, freezing and depuration may achieve “fresh” characteristics under certain processing conditions. Nonetheless, pathogens are likely to survive during storage, and processing times range between 2 hours to a couple of days (Table 3). Likewise, pathogens may survive exposure to chemical compounds. In this case, the potential risk of residues are of consumer concern and some of these compounds are strong oxidation agents that may trigger non-desirable reactions like lipid oxidation. Irradiation is close to deliver the food safety and quality achieved by HPP, although it is not well perceived among consumers, does not shuck shellfish and is legally restricted in some countries. Thermal processing is the only alternative capable of yielding shelf stable foods, but the final quality of the product is severely affected.

Table 3. Food processing alternatives to reduce Vibrio spp. in shellfish.

*Intervention Description **Vibrio spp.

effectiveness

Advantages

Disadvantages

HPP Shellfish are introduced into a metal vessel. Pressurized cold water (4-25 °C/40-75 °F) is pumped to raise pressure between 3,000-6,000 bar/45,000-87,000 psi. 3 • Achieves Vibrio spp. reduction standard.

• Retains sensorial and nutritional quality of raw shellfish.

• Shucks shellfish to yield up to 100% meat recovery.

• Short processing times (0.5-1.5 min holding time).

• Uniform and instantaneous pressure transmission.

• Initial unit investment

• Does not eliminate bacterial spores

Rapid cooling Assures reduced cooling time from 20ºC to 4ºC 1-2 • Reduces time for microbial recovery and growth • Does not achieve Vibrio spp. reduction standard
Irradiation Exposes foods to high intensity energy beams such as gamma rays or X-rays 3 • Achieves Vibrio spp. reduction standard

• Retains sensorial and nutritional quality of raw shellfish

• Negative consumer perception due to misconceived radioactivity

• Does not shuck shellfish

• Legally restricted

Thermal Applies heat to pasteurize (50-90 °C) or sterilize (121 °C/250 °F or higher) foods 3 • Achieves Vibrio spp. reduction standard

• Delivers shelf stable products under severe conditions (121 °C; 250 °F)

• Does not achieve “fresh” like products.

• Negatively impacts the sensorial and nutritional attributes of foods

Freezing Reduce the product temperature to -18ºC or below 2 • Extends shelf life of products by stopping microorganisms growth and slowing chemical changes, such us enzymatic reactions • Texture alteration and water loss due to ice cristal formation

• Pathogens may survive during storage

Depuration Maintains bivalves in clean sea water to enhance the excretion of any contaminants and prevent their re-uptake 1-2 • Reduces the risk of infection • Does not achieve Vibrio spp. reduction standard

• Requires extended times (e.g. 2 days)

Chemical Addition of food preservatives to inactivate microorganisms or delay their growth and prevent quality loss 2-3 • May achieve Vibrio spp. reduction standard • Pathogens may survive

• Chemical agents are typically strong oxidizers that negatively impact food quality

• Public concerns on chemical residues

• Chemical hazard in processing facilities

* Intervention ranking (except for chemical) based on consumer perception of final product as reported by FAO.

** 0: no effect; 1: slight reduction; 2: moderate reduction; 3 significant reduction

If you want to know more about the HPP technology and how to improve the food safety and the quality of your products, contact us, the world leading manufacturer of High Pressure Processing (HPP) equipment for the food industry.

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