Shellstock White Paper

Development of smart TTI-labels indicating risk of Vibrio growth in fresh molluscan shellfish for human consumption.

Peter Ronnow, Ph.D., Vitsab International AB, Sweden

Back ground:

Vibrio vulnificus and Vibrio parahaemolyticus are bacteria that occur naturally in warm coastal waters. These bacteria grow quickly after harvest of molluscan shellfish, at high ambient temperature 65 – 90°F and can result in significant numbers especially during the summer harvest. Thus posing a health risk if oysters with high numbers of Vibrio spp. are ingested raw. From 1989 to 2002, the U.S. FDA recorded 341 serious illnesses associated with consumption of raw shellfish containing Vibrio vulnificus bacteria.  98% of these cases were from consuming raw oysters. 179 people, over 52%, died from their sickness (UC Food safety bulletin). The Center for Disease Control and Prevention (CDC) started monitoring Vibrio parahaemolyticus in costal-waters of USA in May 2013 in 13 states with federal and state partners. By the end of September there were 104 cases of vibriosis reported from consuming raw or undercooked shellfish, primarily oysters (CDC, 2013).


Vibrio spp. infection associated with consumption of shellfish figs. 1 and 2



The American Health Authority; FDA, have guidelines advising how to handle seafood products, avoiding it to become a hazardous food (FDA 2011). In advising on different methods which include the use of appropriate TTIs can thereby limit specific health risks e.g. growth of Clostridium botulinum and its toxin formation in seafood products. Vitsab has in the past designed the L5-8 Seafood TTI according to FDA’s C. bot. concerns (fig.3). This labels is in commercial use for more than a decade and widely used by seafood producers in different parts of the world, as a means to comply with FDA guidelines monitoring transports of fresh seafood products. Fresh salmon, fresh tuna export to USA as well as for tinned crab meat and scallops transported within USA also use the L5-8 label complying with FDA guidelines.

 Fig. 3Mathcad - Skinner_Larkin - L5-8 fitness 140305.xmcd



Adaptation of TTI-formulation to risk of Vibrio spp. growth in molluscan shellfish.

Growth of Vibrio spp. in shellfish after harvest is a typical time-temperature relationship which can be used as a predictive model for growth of Vibrio species. Vitsab has developed suitable TTI-formulations together with FDA researchers and with Kristin Derosia-Banik, State of Connecticut, Department of Agriculture, Bureau of Aquaculture and Laboratory services. During the summer of 2015 several formulations were used during harvest. The oysters were harvested in Long Island Sound outside the town Norwalk by a local oyster producer. At harvest the oysters close up and during storage on boat deck the temperature inside oysters quickly rise to levels where Vibrio species have high or very high growth rates and can within in a number of hours, reach several doublings composing a significant health risk when consumed raw. It was suggested by Kristin Derosia-Banik to the oyster growers to use some kind of temperature control during harvest trying to minimize Vibrio counts.


The Vitsab Oyster-Vibrio TTI-labels VP-1 and VP-3 were designed to fit to the predicted growth of one and three doublings respectively of Vibrio parahaemolyticus in the temperature range 60 – 90°F. The VP labels are based on M-type enzymatic TTI and for Vibrio vulnificus the TTI-labels VV-1 and VV-3 are based on the lipid substrate methyl stearate. All TTI-formulations are designed to fit the growth model of one and three doublings for the two Vibrio species. The growth model data were obtained from John Bowers, FDA, USA (John Bowers, 2015). The response pattern of the Vibrio labels in the temperature range 60 – 90°F can be compared to the growth models of Vibrio p. and Vibrio v. for one


Mathcad - Shellstock P1.xmcd


Mathcad - Shellstock V1.xmcd

doubling in figs. 4 and 5 respectively. These results clearly indicate that the response of the Vitsab Vibrio TTI-labels closely follow the growth models of the two Vibrio species


For testing and validating harvest procedures with different cooling regimes a number of oysters were equipped with temperature logger inserted inside the oyster shell. After completed handling the temperature loggers were evaluated and some data used calculate the color progression of the Vibrio labels through a numerical integration of the temperature profile of the internal oyster temperature.


To illustrate temperature exposure in oysters that are not chilled directly after harvest a temperature logger was inserted into an oyster monitoring in situ oyster temperatures. From the data In fig. 6 it is clear that oyster temperatures remain high and above 80°F for more than 5 hours before the harvest has been off loaded and lifted into cooling facilities at landing dock Harvest 15-08-18. At these high internal oyster temperatures the Vibrio species will quickly grow into high numbers which will constitute a significant health risk when ingested raw or undercooked by humans.

Fig. 6

Internal oyster temp


Other oyster harvest regimes with rapid cooling methods are listed in Table 1. compered with calculated color progression of the VP-1, VP-3 and VV-1 and VV-3 TTI-labels from corresponding internal oyster temperatures.


Tabel 1Table 1



The results from the performed field test clearly confirm that a rapid cooling of harvested oysters in an efficient cooling procedure will limit any further growth of Vibrio species occurring in local waters. It is also clear that the Vibrio-Oyster TTI-labels is a useful instrument to monitor the harvest procedures if cooling procedures are not applied.

In the present oyster harvest study using the Vibrio-Oyster TTI-labels, designed to indicate if Vibrio spp. growth have exceeded either one or three doublings, clearly indicate that these Vibrio-TTIs are a useful and powerful tool in validating improved handling and cooling procedures. The developed TTI-labels are also a perfect means to monitor the further distribution from oyster’s harvester/producer out to customers, locally as well as for longer national transports.