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Publication #FSHN13-12

Survival of Foodborne Pathogens on Berries1

Mary Palumbo, Linda J. Harris, and Michelle D. Danyluk2

Introduction

Fresh and frozen berries are popular foods. When berries are picked for fresh consumption, they are usually packed directly without washing because they are highly perishable. Fresh berries also are commonly included in fresh-cut fruit mixtures sold as a ready-to-eat product. Berries may be washed before freezing, but they are not usually blanched or heat-treated unless they will be used in preserves or other processed products. There is typically no “kill step” that would eliminate pathogens on fresh or frozen berries.

Foodborne illness outbreaks have been associated with the consumption of fresh or frozen berries that were contaminated with pathogenic viruses, parasites, or bacteria. Contamination can occur before or during harvest or during final preparation (Palumbo et al. 2013). The majority of outbreaks have been caused by viruses or parasites, and many of the virus-associated outbreaks have been linked to frozen berries. Outbreaks caused by viruses and parasitic coccidia are likely underreported because these pathogens are much more difficult to isolate and to study in the laboratory. Bacteria can be cultured on laboratory media, but viruses and coccidia require a host cell, often in the form of tissue culture. Norovirus, a common intestinal pathogen, cannot be grown in cell culture with currently available methods. Norovirus can be studied indirectly by using surrogate viruses or with non-culture methods that use a technique known as reverse transcription PCR. This publication summarizes studies on the survival of pathogenic microorganisms on berries.

Outbreaks Caused by Viral Contamination

A large norovirus outbreak occurred in Germany in 2012 when contaminated frozen strawberries were delivered by a catering firm to almost 500 schools and daycare centers (Bourquin 2012). Hepatitis A outbreaks have been associated with blueberries (Calder et al. 2003), raspberries (Ramsey and Upton 1989; Reid and Robinson 1987), and strawberries (CDC 1997a; Hutin et al. 1999; Niu et al. 1992). An outbreak of hepatitis A associated with frozen mixed berries originated in Denmark, Finland, Norway, and Sweden in October 2012; the strawberries in the mixture were eventually considered the likely cause (Nordic outbreak investigation team 2013). Viruses can survive frozen storage, and this ability contributes to geographically and temporally widespread outbreaks.

Outbreaks Involving Coccidian Parasites

Cyclosporiasis outbreaks caused by Cyclospora cayetanensis have been associated with imported raspberries. A series of outbreaks occurred between 1996 and 2000 that were ultimately attributed to Guatemalan raspberries (CDC 1996, 1997b, 1997c, 1998; Herwaldt and Beach 1999; Ho et al. 2002; Murrow et al. 2002). In 2008, C. cayetanensis outbreaks occurred in California and Tennessee; berries were identified as the food vehicle, but the type of berry was not specified (CDC 2013; Marler-Clark 2013). C. cayetanensis is difficult to study because humans are its only known host. A related parasite, Toxoplasma gondii, which causes illness in humans and can be transmitted by food, was used in one study of survival on raspberries and blueberries (Kniel et al. 2002).

Outbreaks Involving Bacterial Pathogens

Three outbreaks have been reported involving berries contaminated with bacterial pathogens. In 2006, five people were reported ill with E. coli O26, and the food vehicle was believed to be strawberries, blueberries, or a mix of both berries (Luna and Mody 2010). In 2009, a multistate outbreak of Salmonella Muenchen was detected when 14 people became ill from consuming contaminated blueberries (CDC 2013). And in 2011, 15 people became ill with E. coli O157:H7 in Oregon; matching isolates of the outbreak strain were obtained by environmental sampling in the field where the implicated strawberries were grown (Laidler et al. 2013; Oregon Public Health 2011; Terry 2011).

Available Survey Data

Limited survey data are available on the prevalence of pathogenic microorganisms on berries. In all cases the number of samples evaluated were too low to be statistically robust. Robertson and Gjerde (2001) determined the occurrence of parasites on various fresh fruits and vegetables available in Norway. Strawberries from Belgium, Egypt, Israel, Italy, and Norway were tested for Cyclospora oocysts (30 approximately 100-g samples), Cryptosporidium oocysts, and Giardia cysts (62 approximately 100-g samples for each). None of the samples were positive for Cyclospora or Cryptosporidium; two were positive for Giardia. Strawberries were included in a survey of produce grown in Alberta, Canada (Bohaychuk et al. 2009), and were tested by enrichment for the presence of Salmonella spp., E. coli O157:H7, and Campylobacter spp., and for Cryptosporidium spp. All 31 25-g samples were negative for the pathogens tested. Mukherjee et al. (2006) collected produce samples from conventional and organic farms in Wisconsin and Minnesota and tested for the presence of Salmonella spp. and E. coli O157:H7. A total of 126 25-gram samples of strawberries, raspberries, and blueberries (breakdown by berry not given) were examined using standard enrichment culture; none were positive for these pathogens. A survey of raspberries and strawberries from European sources found four of 10 20-g samples of raspberries and six of 20 20-g samples of strawberries were positive for norovirus, using a reverse transcription quantitative PCR method for detection (Stals et al. 2011). The authors noted that differentiation between infectious and noninfectious virus particles was not possible with this method.

Current Publication

This publication is a summary of the data on the survival of foodborne pathogens in fresh and frozen blueberries, raspberries, and strawberries (Tables 1–4). Data for other berries were not available. Although the freeze-thaw cycle may reduce pathogen viability, these laboratory and outbreak data provide clear evidence that, for many pathogens, viability and virulence are retained in frozen storage.

Survival of viruses is summarized in Tables 1–3. Prompted by the occurrence of large outbreaks of hepatitis A and norovirus associated with frozen berries, Butot et al. (2008) studied the effect of frozen storage on hepatitis A virus, norovirus, rotavirus, and feline calicivirus (used as a surrogate for norovirus) inoculated onto blueberries, raspberries, and strawberries. Freezing did not significantly reduce the viability of any of the viruses, with the exception of feline calicivirus on strawberries. Frozen storage for up to 3 months had a limited effect on survival of hepatitis A and rotavirus in the berries studied. Feline calicivirus infectivity declined on strawberries and raspberries, presumably due to their low pH. At room temperature, murine norovirus and human adenovirus decayed rapidly on strawberries but survived to the end of the shelf life of raspberries. At 4oC, no decay was observed for murine norovirus on either berry, and human adenovirus decayed only slightly (Verhaelen et al. 2012). These results illustrate the importance of using data obtained with the berry of interest when developing food safety plans.

Survival of coccidian pathogens has been evaluated on blueberries and raspberries (Tables 1 and 2). In contrast to norovirus and hepatitis A, outbreaks of cyclosporiasis have been attributed to fresh berries rather than frozen (Palumbo et al. 2013). Lee and Lee (2001) used Eimeria acervulina, a coccidian from the same family as Cyclospora, as a surrogate in studies on raspberries, and showed that infectivity was lost after freezing. Kniel et al. (2002) studied the attachment and survival of Toxoplasma gondii oocysts on raspberries and blueberries. In these studies, mice developed acute infections after being fed T. gondii-inoculated raspberries and blueberries that had been stored under refrigeration for up to 8 weeks.

Survival of E. coli O157:H7, Salmonella spp., and Listeria monocytogenes has been studied on intact and cut strawberries at room and refrigeration temperatures and during frozen storage (Table 4; Flessa et al. 2005; Han et al. 2004; Knudsen et al. 2001; Yu et al. 2001). No growth was observed for these pathogens on the surface of strawberries in any of the studies, though all of the pathogens were able to survive.

The information should be useful for growers and handlers of fresh berries who are developing food safety plans. The information is organized into four tables:

Table 1. Blueberries: Survival of viruses and parasites

Table 2. Raspberries: Survival of viruses and parasites

Table 3. Strawberries: Survival of viruses

Table 4. Strawberries: Growth and survival of pathogenic bacteria

References

Bohaychuk, V. M., R. W. Bradbury, R. Dimock, M. Fehr, G. E. Gensler, R. K. King, R. Rieve, and P. R. Barrios. 2009. A microbiological survey of selected Alberta-grown fresh produce from farmers' markets in Alberta, Canada. J. Food Prot. 72 (2): 415–420.

Bourquin, L. 2012. Strawberries implicated in massive German norovirus outbreak. Michigan State University Food Safety. Accessed April 2013. http://michiganstateuniversityfoodsafety.wordpress.com/2012/10/07/strawberries-implicated-in-massive-german-norovirus-outbreak/.

Butot, S., T. Putallaz, and G. Sanchez. 2008. Effects of sanitation, freezing and frozen storage on enteric viruses in berries and herbs. Int. J. Food Microbiol. 126 (1–2): 30–35.

Calder, L., G. Simmons, C. Thornley, P. Taylor, K. Pritchard, G. Greening, and J. Bishop. 2003. An outbreak of hepatitis A associated with consumption of raw blueberries. Epidemiol. Infect. 131 (1): 745–751.

Centers for Disease Control and Prevention (CDC). 1996. Update: Outbreaks of Cyclospora cayetanensis infection—United States and Canada, 1996. MMWR Weekly 45 (28): 611–612. http://www.cdc.gov/mmwr/preview/mmwrhtml/00043133.htm.

Centers for Disease Control and Prevention (CDC). 1997a. Hepatitis A associated with consumption of frozen strawberries—Michigan, March 1997. MMWR Weekly 46 (13): 288, 295. http://www.cdc.gov/mmwr/preview/mmwrhtml/00047129.htm.

Centers for Disease Control and Prevention (CDC). 1997b. Update: Outbreaks of cyclosporiasis—United States, 1997. MMWR Weekly 46 (21): 461–462. http://www.cdc.gov/mmwr/preview/mmwrhtml/00047716.htm.

Centers for Disease Control and Prevention (CDC). 1997c. Outbreak of cyclosporiasis—Northern Virginia-Washington, D.C.-Baltimore, Maryland, Metropolitan Area. MMWR Weekly 46 (30): 689–691. http://www.cdc.gov/mmwr/preview/mmwrhtml/00048551.htm.

Centers for Disease Control and Prevention (CDC). 1998. Outbreak of cyclosporiasis—Ontario, Canada, May 1998. MMWR Weekly 47 (38): 806–809. http://www.cdc.gov/mmwr/preview/mmwrhtml/00055016.htm.

Centers for Disease Control and Prevention (CDC). 2013. Foodborne Outbreak Online Database [CDC FOOD]. Accessed January 2013. http://wwwn.cdc.gov/foodborneoutbreaks/Default.aspx.

Flessa, S., D. M. Lusk, and L. J. Harris. 2005. Survival of Listeria monocytogenes on fresh and frozen strawberries. Int. J. Food Microbiol. 101 (3): 255–262.

Han, Y., R. H. Linton, and P. E. Nelson. 2004. Effects of recovery, plating, and inoculation methods on quantification of Escherichia coli O157:H7 and Listeria monocytogenes from strawberries. J. Food Prot. 67 (11): 2436–2442.

Herwaldt, B. L., and M. J. Beach. 1999. The return of Cyclospora in 1997: another outbreak of cyclosporiasis in North America associated with imported raspberries. Cyclospora Working Group. Ann. Intern. Med. 130 (3): 210–220.

Ho, A. Y., A. S. Lopez, M. G. Eberhard, R. Levenson, B. S. Finkel, A. J. da Silva, J. M. Roberts, P. A. Orlandi, C. C. Johnson, and B. L. Herwaldt. 2002. Outbreak of cyclosporiasis associated with imported raspberries, Philadelphia, Pennsylvania, 2000. Emerg. Infect. Dis. 8 (8): 783–788.

Hutin, Y. J. F., V. Pool, E. H. Cramer, O. V. Nainan, J. Weth, I. T. Williams, S. T. Goldstein, K. F. Gensheimer, B. P. Bell, C. N. Shapiro, M. J. Alter, and H. S. Margolis. 1999. A multistate, foodborne outbreak of hepatitis A. New Eng. J. Med. 340 (8): 595–602.

Kniel, K. E., D. S. Lindsay, S. S. Sumner, C. R. Hackney, M. D. Pierson, and J. P. Dubey. 2002. Examination of attachment and survival of Toxoplasma gondii oocysts on raspberries and blueberries. J. Parasitol. 88 (4): 790–793.

Knudsen, D. M., S. A. Yamamoto, and L. J. Harris. 2001. Survival of Salmonella spp. and Escherichia coli O157:H7 on fresh and frozen strawberries. J. Food Prot. 64 (10): 1483–1488.

Kurdziel, A. S., N. Wilkinson, S. Langton, and N. Cook. 2001. Survival of poliovirus on soft fruit and salad vegetables. J. Food Prot. 64 (5): 706–709.

Laidler, M. R., M. Tourdjman, G. L. Buser, T. Hostetler, K. K. Repp, R. Leman, M. Samadpour, and W. E. Keene. 2013. Escherichia coli O157:H7 infections associated with consumption of locally grown strawberries contaminated by deer. Clin. Infect. Dis. 57 (8): 1129–1134.

Lee, M. B., and E. H. Lee. 2001. Coccidial contamination of raspberries: mock contamination with Eimeria acervulina as a model for decontamination treatment studies. J. Food Prot. 64 (11): 1854–1857.

Luna, R. E., and R. Mody. 2010. Non-O157 Shiga toxin-producing E. coli (STEC) outbreaks, United States. CDC Memo to Record. Accessed April 2013. http://blogs.cdc.gov/publichealthmatters/files/2010/05/nono157stec_obs_052110.pdf.

Marler-Clark, LLP. 2013. Foodborne Illness Outbreak Database. http://outbreakdatabase.com Accessed April 2013.

Mattison, K., K. Karthikeyan, M. Abebe, N. Malik, S. A. Sattar, J. M. Farber, and S. Bidawid. 2007. Survival of calicivirus in foods and on surfaces: experiments with feline calicivirus as a surrogate for norovirus. J. Food Prot. 70 (2): 500–503.

Mukherjee, A., D. Speh, A. T. Jones, K. M. Buesing, and F. Diez-Gonzalez. 2006. Longitudinal microbiological survey of fresh produce grown by farmers in the upper Midwest. J. Food Prot. 69 (8): 1928–1936.

Murrow, L. B., P. Blake, and L. Kreckman. 2002. Outbreak of cyclosporiasis in Fulton County, Georgia. Georgia Epidemiol. Rep. 18 (1): 1–2.

Niu, M.T., L. B. Polish, B. H. Robertson, B. K. Kanna, B. A. Woodruff, C. N. Shapiro, M. A. Miller, J. D. Smith, J. K. Gedrose, M. J. Alter, and H. S. Margolis. 1992. Multistate outbreak of hepatitis A associated with frozen strawberries. J. Infect. Dis. 166 (3): 518–524.

Nordic outbreak investigation team. 2013. Joint analysis by the Nordic countries of a hepatitis A outbreak, October 2012 to June 2013: frozen strawberries suspected. Euro Surveill. 18 (27) pii: 20520.

Oregon Public Health. 2011. Fresh strawberries from Washington County farm implicated in E. coli O157 outbreak in NW Oregon. Accessed September 2013. http://www.fda.gov/Safety/Recalls/ArchiveRecalls/2011/ucm267667.htm.

Palumbo, M., L. J. Harris, and M. D. Danyluk. 2013. Outbreaks of foodborne illness associated with common berries, 1983 through May 2013. Gainesville: University of Florida Institute of Food and Agricultural Sciences. http://edis.ifas.ufl.edu/fs232.

Ramsay, C. N., and P. A. Upton. 1989. Hepatitis A and frozen raspberries. Lancet 1 (8628): 43–44.

Reid, T. M. S., and H. G. Robinson. 1987. Frozen raspberries and hepatitis A. Epidemiol. Infect. 98 (1): 109–112.

Robertson, L. J., and B. Gjerde. 2001. Occurrence of parasites on fruits and vegetables in Norway. J. Food Prot. 64 (11): 1793–1798.

Stals, A., L. Baert, V. Jasson, E. Van Coillie, and M. Uyttendaele. 2011. Screening of fruit products for norovirus and the difficulty of interpreting positive PCR results. J. Food Prot. 74 (3): 425–431.

Terry, L. 2011. Oregon confirms deer droppings caused E. coli outbreak tied to strawberries. The Oregonian. Accessed September 2013. http://www.oregonlive.com/washingtoncounty/index.ssf/2011/08/oregon_confirms_deer_droppings.html.

Verhaelen, K., M. Bouwknegt, F. Lodder-Verschoor, S. A. Rutjes, and A. M. de Roda Husman. 2012. Persistence of human norovirus GII.4 and GI.4, murine norovirus, and human adenovirus on soft berries as compared with PBS at commonly applied storage conditions. Int. J. Food Microbiol. 160 (2): 137–144.

Yu, K., M. C. Newman, D. D. Archbold, and T. R. Hamilton-Kemp. 2001. Survival of Escherichia coli O157:H7 on strawberry fruit and reduction of the pathogen population by chemical agents. J. Food Prot. 64 (9): 1334–1340.

Tables

Table 1. 

Blueberries: Survival of viruses and parasites

Pathogen

Fruit product

Method of inoculation

Storage conditions

Temp (°C)

Initial counts

Storage time

Results

Unit

Comments

Reference

Feline calicivirus

Whole, 15 g portion

Spot inoculated (50 µl over 10 spots), air dried for 60 min

Freezing for 2, 30, and 90 days

-20

6.2 log TCID501 on 15 g portions

2 days (data not shown for 30 and 90 days)

Survival (see comment)

-0.6 ± 0.09

PCRU2

Decay of viruses calculated as log(Nx/N0) where N0 is infectious virus titer for untreated produce, Nx is infectious titer for treated produce

Butot et al. 2008

Survival (see comment)

0.3 ± 0.15

TCID50

Hepatitis A virus

Whole, 15 g portion

Spot inoculated (50 µl over 10 spots), air dried for 60 min

Freezing for 2, 30, and 90 days

-20

6.2 log TCID50 on 15 g portions

2 days (data not shown for 30 and 90 days)

Survival (see comment)

0.0 ± 0.18

PCRU

Decay of viruses calculated as log(Nx/N0) where N0 is infectious virus titer for untreated produce, Nx is infectious titer for treated produce

Butot et al. 2008

Survival (see comment)

-0.4 ± 0.19

TCID50

Norovirus GI and GII

Whole, 15 g portion

Spot inoculated (50 µl over 10 spots), air dried for 60 min

Freezing for 2, 30, and 90 days

-20

5.1 log PCRU of NV GI,

6.3 log PCRU of NV GII on 15 g portions

2 days (data not shown for 30 and 90 days)

Survival

-0.9 ± 0.07 (NV GI)

-0.9 ± 0.09 (NV GII)

PCRU

Survival assessed by RT-PCR3, no method for propagating in vitro

Butot et al. 2008

Rotavirus

Whole, 15 g portion

Spot inoculated (50 µl over 10 spots), air dried for 60 min

Freezing for 2, 30, and 90 days

-20

4.6 log TCID50 on 15 g portions

2 days (data not shown for 30 and 90 days)

Survival (see comment)

-0.8 ± 0.15

PCRU

Decay of viruses calculated as log(Nx/N0) where N0 is infectious virus titer for untreated produce, Nx is infectious titer for treated produce

Butot et al. 2008

Survival (see comment)

-1.2 ± 0.13

TCID50

Toxoplasma gondii VEG strain oocysts

Whole

Spot inoculation with 1 mL inoculum per berry, air dried 2 min

Refrigeration, RH not given

4

2 x 104

2, 4, 6, and 8 weeks

All mice fed contaminated berries after storage became infected

3 mice fed at each storage time; 0 mice positive in control

Dose titration also conducted

Kniel et al. 2002

Notes to Table 1:

1 TCID50, 50% tissue culture infective dose

2 PCRU, PCR unit

3 RT-PCR, reverse transcription–PCR

Table 2. 

Raspberries: Survival of viruses and parasites

Pathogen

Fruit product

Method of inoculation

Storage conditions

Temp (°C)

Initial counts

Storage time

Results

Unit

Comments

Reference

Eimeria acervulina (surrogate for Cyclospora cayetanensis)

Whole

Berry dipped in suspension of oocysts

Freezing

-18

Expt 1: 400 oocysts

Expt 2: 650 oocysts

24 h

Frozen mashed berries used as inoculum, fed to 2-day-old chicks; evaluated 5 days post inoculation for duodenal lesions and/or presence of oocysts in cecal contents or at 6 days post inoculation for oocysts in feces: 0/5 chicks positive in each of two experiments (5/5 chicks positive in controls)

Reported as positive or negative chicks

Freezing destroyed infectivity

Lee and Lee 2001

Feline calicivirus

Whole, 15 g portion

Spot inoculated (50 µl over 10 spots), air dried for 60 min

Freezing for 2, 30, and 90 days

-20

6.2 log TCID501 on 15 g portions

2 days (data not shown for 30 and 90 days)

Survival (see comment)

-0.6

PCRU2

Decay of viruses calculated as log(Nx/N0) where N0 is infectious virus titer for untreated produce, Nx is infectious titer for treated produce

Butot et al. 2008

Survival (see comment)

-1.1

Numbers recovered declined progressively in storage, TCID50 values reduced by >2 log units

TCID50

Hepatitis A virus

Whole, 15 g portion

Spot inoculated (50 µl over 10 spots), air dried for 60 min

Freezing for 2, 30, and 90 days

-20

6.2 log TCID50 on 15 g portions

2 days (data not shown for 30 and 90 days)

Survival (see comment)

0.0

PCRU

Decay of viruses calculated as log (Nx/N0) where N0 is infectious virus titer for untreated produce, Nx is infectious titer for treated produce

Butot et al. 2008

Human adenovirus

Whole, 25 g portion

3 x 100 µl inoculum applied in small drops on surface

Refrigerated incubators and room temp; RH 70%, 58%, and 36%, respectively

4

10

21

1 x 106 virus particles applied

1, 2, 3, 5, and 7 days (21°C storage terminated at 3 days)

4°C: 0.1 (PCR), 0.4 (CC3)

10°C: 0.2 (PCR, CC)

21°C: 0.5 (PCR), 0.3 (CC)

Mean log reduction in viral titer

Persistence expressed as reduction in viral titer after 7 days at 4°C and 10°C, 3 days at 21°C

Verhaelen et al. 2012

Murine norovirus

Whole, 25 g portion

3 x 100 µl inoculum applied in small drops on surface

Refrigerated incubators and room temp; RH 70%, 58%, and 36%, respectively

4

10

21

4 x 105 virus particles applied

1, 2, 3, 5, and 7 days (21°C storage terminated at 3 days)

4°C: 0 (PCR, CC)

10°C: 0 (PCR), 0.5 (CC)

21°C: 0.5 (PCR), 1.1 (CC)

TFL4 was 3 days at 21°C; 1 log reduction not achieved at 4°C or 10°C within study time

Mean log reduction in viral titer

Persistence expressed as reduction in viral titer after 7 days at 4°C and 10°C, 3 days at 21°C and for TFL

Verhaelen et al. 2012

Norovirus GI and GII

Whole, 15 g portion

Spot inoculated (50 µl over 10 spots), air dried for 60 min

Freezing for 2, 30, and 90 days

-20

5.1 log PCRU of NV GI,

6.3 log PCRU of NV GII on 15 g portions

2 days (data not shown for 30 and 90 days)

Survival: 0.1 (NV GI), 0.0 (NV GII) as determined by RT-PCR5; authors report that most viruses studied were reduced by less than 1 log by freezing

PCRU

Decay of viruses calculated as log(Nx/N0) where N0 is infectious virus titer for untreated produce, Nx is infectious titer for treated produce

Butot et al. 2008

Norovirus GII.4 and GI.4

Whole, 25 g portion

3 x 100 µl inoculum applied in small drops on surface

Refrigerated incubators and room temperature; RH 70%, 58%, 36%, respectively

4

10

21

8 x 106 genomic copies of GI, 2 x 106 copies of GII

1, 2, 3, 5, and 7 days (21°C storage terminated at 3 days)

4°C: 0 (GI, GII)

10°C: 0.4 (GI), 0.3 (GII)

21°C: 0.3 (GI), 0.2 (GII)

Mean log10 reduction in viral titer by PCR

Persistence expressed as reduction in viral titer after 7 days at 4°C and 10°C, 3 days at 21°C

Verhaelen et al. 2012

Poliovirus type 1a

Whole

1 mL virus suspension added to 60g of fruit

Refrigeration, sealed stomacher bags

4

~ 5 log TCID50

1, 4, and 9 days

No significant decline (exact counts not given)

TCID50

Raspberries severely deteriorated by day 9

Kurdziel et al. 2001

Rotavirus

Whole, 15 g portion

Spot inoculated (50 µl over 10 spots), air dried for 60 min

Freezing for 2, 30, and 90 days

-20

4.6 log TCID50 on 15 g portions

2 days (data not shown for 30 and 90 days)

Survival (see comment)

0.2

PCRU

Decay of viruses calculated as log (Nx/N0) where N0 is infectious virus titer for untreated produce, Nx is infectious titer for treated produce

Butot et al. 2008

Survival (see comment)

0.9

TCID50

Toxoplasma gondii VEG strain oocysts

Whole

Spot inoculation with 1 mL inoculum per berry, air dried 2 min

Refrigeration, RH not given

4

2 x 104

2, 4, 6 and 8 weeks

All mice fed contaminated berries after storage became infected

3 mice fed at each storage time; 0 mice positive in control

Dose titration also conducted

Kniel et al. 2002

1 TCID50, 50% tissue culture infective dose

2 PCRU, PCR unit

3 CC, cell culture

4 TFL, time required for first log10-unit reduction in titer

5 RT-PCR, reverse transcription–PCR

Table 3. 

Strawberries: Survival of viruses

Pathogen

Fruit product

Method of inoculation

Storage conditions

Temp (°C)

Initial counts

Storage time

Results

Unit

Comments

Reference

Feline calicivirus

Whole, 15 g portion

Spot inoculated (50 µl over 10 spots), air dried for 60 min

Freezing for 2, 30, and 90 days

-20

6.2 log TCID501 on 15 g portions

2 days (data not shown for 30 and 90 days)

Survival (see comment) -0.2

PCRU2

Decay of viruses calculated as log(Nx/N0) where N0 is infectious virus titer for untreated produce, Nx is infectious titer for treated produce

Butot et al. 2008

Survival (see comment) -2.7

TCID50 values continued slower decline because of diminishing inactivation rate

TCID50

Feline calicivirus

Sliced

10 µl (3 x 105 PFU)

Stored in sterile petri dishes

4

22.5 (room temp)

3.1 x 103 PFU

1 to 7 days

4°C: survived 5 days, <100 at 6 days

22.5°C: <100 at 2 days

PFU

Data presented in bar graphs

Mattison et al. 2007

Hepatitis A virus

Whole, 15 g portion

Spot inoculated (50 µl over 10 spots), air dried for 60 min

Freezing for 2, 30, and 90 days

-20

6.2 log TCID50 on 15 g portions

2 days (data not shown for 30 and 90 days)

Survival (see comment)

0.7

PCRU

Decay of viruses calculated as log(Nx/N0) where N0 is infectious virus titer for untreated produce, Nx is infectious titer for treated produce

Butot et al. 2008

Survival (see comment)

0.00

TCID50

Human adenovirus

Whole, 20 to 30 g

3 x 100 µl inoculum applied in small drops on surface

Refrigerated incubators and room temperature; RH 70%, 58%, 36%, respectively

4

10

21

1 x 106 virus particles applied

1, 2, 3, 5, and 7 days (21°C storage terminated at 3 days)

4°C: 0.6 (PCR), 0.2 (CC3)

10°C: 0 (PCR), 1.2 (CC)

21°C: 0 (PCR), 1.9 (CC)

TFL4: 10°C, 6 days (CC); 21°C, 1 day (CC)

Mean log reduction in viral titer

Persistence expressed as reduction in viral titer after 7 days at 4°C and 10°C, 3 days at 21°C and for TFL

Verhaelen et al. 2012

Murine norovirus

Whole, 20 to 30 g

3 x 100 µl inoculum applied in small drops on surface

Refrigerated incubators and room temperature; RH 70%, 58%, 36%, respectively

4

10

21

4 x 105 virus particles applied

1, 2, 3, 5, and 7 days (21°C storage terminated at 3 days)

4°C: 0 (PCR, CC)

10°C: 0.3 (PCR), 0.9 (CC)

21°C: 0.9 (PCR), 1.4 (CC)

TFL: 10°C, 7 days; 21°C, 3 days (PCR), 1 day (CC)

Mean log reduction in viral titer

Persistence expressed as reduction in viral titer after 7 days at 4°C and 10°C, 3 days at 21°C and for TFL

Verhaelen et al. 2012

Norovirus GI and GII

Whole, 15 g portion

Spot inoculated (50 µl over 10 spots), air dried for 60 min

Freezing for 2, 30, and 90 days

-20

5.1 log PCRU of NV GI,

6.3 log PCRU of NV GII on 15 g portions

2 days (data not shown for 30 and 90 days)

-0.1, -0.4 as determined by RT-PCR5 (cannot be grown in cell culture)

PCRU, 2nd no. is NV GII

Survival assessed by RT-PCR, no method for propagating in vitro

Butot et al. 2008

Norovirus GII.4 and GI.4

Whole, 20 to 30 g

3 x 100 µl inoculum applied in small drops on surface

Refrigerated incubators and room temperature; RH 70%, 58%, 36%, respectively

4

10

21

8 x 106 genomic copies of GI, 2 x 106 copies of GII

1, 2, 3, 5, and 7 days (21°C storage terminated at 3 days)

4°C: 0 (GI, GII)

10°C: 0.5 (GI), 0.4 (GII)

21°C: 1.2 (GI), 0.5 (GII)

TFL: 21°C, 2 days (GI)

Mean log reduction in viral titer

Persistence expressed as reduction in viral titer after 7 days at 4°C and 10°C, 3 days at 2°C and for TFL

Verhaelen et al. 2012

Poliovirus type 1a

Whole

1 mL virus added to 100g fruit

Freezing, sealed stomacher bags

-20

~4.3 to 5.7 log TCID50

8 and 15 days

90% reduction in inoculated numbers by 8.4 days

TCID50

 

Kurdziel et al. 2001

Rotavirus

Whole, 15 g portion

Spot inoculated (50 µl over 10 spots), air dried for 60 min

Freezing for 2, 30, and 90 days

-20

4.6 log TCID50 on 15 g portions

2 days (data not shown for 30 and 90 days)

Survival (see comment)

0.7

PCRU

Decay of viruses calculated as log(Nx/N0) where N0 is infectious virus titer for untreated produce, Nx is infectious titer for treated produce

Butot et al. 2008

1TCID50, 50% tissue culture infective dose

2PCRU, PCR unit

3CC, cell culture

4TFL, time required for first log10-unit reduction in titer

5RT-PCR, reverse transcription–PCR

Table 4. 

Strawberries: Growth and survival of pathogenic bacteria

Pathogen

Fruit product

pH

Method of inoculation

Treatment and/or storage conditions

Temp (°C)

Initial counts (log CFU)

Incubation time

Final counts (log CFU) or calculated decline

Unit

Comments

Reference

Escherichia coli O157:H7

Whole

 

Dip inoculated

Air dried, held in closed container

21

4

4

4

7.6

2 h

1 day

3 days

7 days

7.2

7.3

6.8

6.0

CFU/ berry

Results shown are for washing and membrane-transfer plating

Han et al. 2004

E. coli O157:H7

Whole

 

100 µl inoculum on surface

Air dried, held in closed container

21

4

4

4

7.6

2 h

1 day

3 days

7 days

7.4

6.9

6.4

5.9

CFU/ berry

Results shown are for washing and membrane-transfer plating

Han et al. 2004

E. coli O157:H7

Whole and cut

3.5

15 µl inoculum on surface

Dried, held in closed container

24

24

7.1

7.0

60 min

48 h

6.5

6.6

CFU/ sample

Results on cut berries were similar

Knudsen et al. 2001

E. coli O157:H7

Whole and cut

3.5

15 µl inoculum on surface

Held in closed container

5

7

7 days

Declined 2 log on whole, no decline on cut

CFU/ sample

 

Knudsen et al. 2001

E. coli O157:H7 ATCC 43895, ATCC 35150

Whole

 

25 µl inoculum on surface

Held in closed container

23

10

5

-20

4.4

4.3

4.3

4.3

24 h

3 days

3 days

3 days

4.6, 3.6

2.2, 2.1

2.9, 2.4

1.5, <1.00

CFU/g

Data also presented for injected inoculum

Yu et al. 2001

Listeria monocytogenes

Whole

 

Dip inoculated

Air dried, held in closed container

21

4

4

4

7.1

2 h

1 day

3 days

7 days

6.7

6.6

5.9

5.2

CFU/ berry

Results shown are for washing and membrane-transfer plating

Han et al. 2004

L. monocytogenes

Whole

 

100 µl inoculum on surface

Air dried, held in closed container

21

4

4

4

7.1

2 h

1 day

3 days

7 days

7.0

6.8

6.2

6.0

CFU/ berry

Results shown are for washing and membrane-transfer plating

Han et al. 2004

L. monocytogenes (5 strains)

Whole and cut

 

15 µl inoculum on intact surface or cut side

Air dried 1 h at room temp, held in loosely closed plastic containers

24

7.5 (high)

5.6 (low)

2 h

24 h

48 h

Whole berries: Declined 0.4 log CFU during drying, 1.0 log CFU after 48 h (high inoculum);

declined 1.0 log during drying, 2.2 log after 48 h (low)

CFU/ sample

On cut berries, counts did not decrease during drying or at low inoculum level after 48 h; at high inoculum level, 0.5 log decline at 48 h

Flessa et al. 2005

L. monocytogenes (5 strains)

Whole and cut

 

15 µl inoculum on intact surface or cut side

Air dried 1 h at room temp, held in loosely closed plastic containers

4

7.7 (high)

5.9 (low, whole) or 5.2 (low, cut)

1 day

4 days

7 days

Whole berries: Declined 0.7 log CFU during drying, 3 log CFU after 7 days (high); declined 1.5 log during drying, 2.7 log after 7 days (low)

CFU/ sample

On cut berries, <1 log decline after 7 days at both inoculum levels

Flessa et al. 2005

L. monocytogenes (5 strains)

Sliced, with and without sucrose

 

Bags of 25 g sliced berries inoculated with 15 µl inoculum, massaged to disperse

Placed flat in single layer in freezer; samples thawed by immersing bag in 25°C water for 8 min

-20

6.7

1 day

7 days

14 days

21 days

28 days

Without added sucrose, declined 0.7 log after 1 day, 1.2 log by 28 days; with sucrose, counts remained stable over 4 weeks

CFU/ sample

 

Flessa et al. 2005

Salmonella (6 serotypes)

Whole

3.5

15 µl inoculum on surface

Air dried, held in closed container

24

24

7.1

7.0

60 min

48 h

6.7

6.3

CFU/ sample

No decline in numbers on cut berries

Knudsen et al. 2001

Salmonella (6 serotypes)

Whole and cut

3.5

15 µl inoculum on surface

Air dried 1 h at room temp, held in closed container

5

7

7 days

Declined 1 to 2 log on whole, declined 0.5 log on cut

CFU/ sample

 

Knudsen et al. 2001

Footnotes

1.

This document is FSHN13-12, one of a series of the Food Science and Human Nutrition Department, UF/IFAS Extension. Original publication date November 2013. Reviewed November 2016. Visit the EDIS website at http://edis.ifas.ufl.edu.

2.

Mary Palumbo, outreach coordinator, Western Center for Food Safety, University of California, Davis, CA 95616; Linda J. Harris, cooperative extension specialist, microbial food safety, Department of Food Science and Technology, University of California, Davis, CA 95616; Michelle D. Danyluk, associate professor, Department of Food Science and Human Nutrition, UF/IFAS Citrus Research and Education Center, Lake Alfred, FL 33850.


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U.S. Department of Agriculture, UF/IFAS Extension Service, University of Florida, IFAS, Florida A & M University Cooperative Extension Program, and Boards of County Commissioners Cooperating. Nick T. Place, dean for UF/IFAS Extension.