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and spreads stored at 21°C than in those stored at 5oC. The pattern of E. coli O157:H7 reduction was generally similar to that of Salmonella (Table 3). The E. coli O157:H7 reductions in samples stored for 1, 2, 3, weeks at 25°C were 2.74, 2.95, and 3.33 log CFU/g, respectively (Table 3). When stored much longer, to 9 weeks at 25°C, E. coli O157:H7 reductions in the peanut butter were significantly higher (P < 0.05) than those of peanut butter stored at 25°C for 1, 2 and 3 weeks (4.46 log CFU/g vs 2.74, 2.95 and 3.33 log CFU/g, respectively). Overall, E. coli O157:H7 cell count reductions of peanut butter stored at 4°C ranged from 2.73 to 3.53 log CFU/g (Table 3). The E. coli O157:H7 was confirmed by the Reveal for E. coli O157:H7 20 h complete system method at 12 and 15 weeks of peanut butter storage. E. coli O157:H7 reductions were significantly (P < 0.05) higher with storage at 25°C than at 4°C for up to 15 weeks of peanut butter storage. These observations are in agreement with previous reports (20) that E. coli O157:H7 reductions in mayonnaise were higher when storage was at room temperature (25°C) than when storage was at refrigeration temperature (4°C). Antibiotic-sensitive Salmonella cell counts in samples stored for 6 and 15 weeks at 25°C were 3.37 and 1.72 log CFU/g, respectively. After 6 and 15 weeks at 25°C, antibiotic-sensitive E. coli O157:H7 showed cell counts of 2.73 and 1.01 log CFU/g, respectively. Survival capacity of antibiotic-resistant mutant strains exhibited slower growth rates, compared with antibiotic-sensitive strains. These results suggest that the use of antibiotic resistance as a selective marker could present different growth rates in laboratory media and show different resistance to stresses. This possibly will result in overestimates of any treatment, such as heat, against antibiotic-sensitive Salmonella and E. coli O157:H7. Findings in this report indicate that post-process contamination of peanut butter with Salmonella and E. coli O157:H7 may result in survival of these pathogens during their shelf life. This premise is in agreement with previous studies showing that Salmonella populations decreased more rapidly in peanut butter at 22°C than at 4oC storage (13). Similar results were observed when Salmonella populations decreased more rapidly in a butter and margarine blend stored at 21°C, compared to 4°C (7). It is most probable that at 25°C, the conditions are highly conducive to bacterial growth in the peanut butter, resulting in accelerated growth and hence attainment of a stationary phase sooner than when storage is at 4°C. It is well documented that storage temperature of colloidal food products influence the availability of Salmonella (13). In our study, Salmonella and E. coli O157:H7 were detected in the peanut butter throughout the storage period. These findings give cause for concern, because previous reports have shown that consumption of even very low numbers of Salmonella or E. coli O157:H7 can cause disease (16). It has also been pointed out that during thermal processing of products such as peanut butter, foodborne pathogens are expected to be eliminated, but post-process contamination may take place during repackaging or with use of ingredients in other food products not subjected to conditions sufficient to kill the pathogens (2). Personal hygiene as well as cross-contamination of finished products with raw materials and unsanitary equipment are significant fundamentals in controlling the contamination of food products with pathogens and spoilage microorganisms (14). ilities must have in place Food Safety Programs to eliminate and control foodborne pathogens in the product. ACKNOWLEDGMENTS This study was supported by US Department of Agriculture (USDA). The authors thank Cindy Thompson and Lou Pearson for their help in the field portions of this work. REFERENCES 1. Blanco, M., J. E. Blanco, A. Mora, J. Rey, J. M. Alonso, M. Hermoso, J. Hermoso, M. P. Alonso, G. Dahbi, E. A.González, M. I. Bernárdez, and J. Blanco. 2003. Serotypes, virulence genes, and intimin types of Shigatoxin (verotoxin)-producing Escherichia coli isolates from healthy sheep in Spain. J. Clin Microbiol. 41:1351–1356. 2. Burnett, S. L., E. R. Gehm, W. R. Weissinger, and L. R. Beuchat. 2000. Survival of Salmonella in peanut butter and peanut butter spread. Appl. Microbiol. 89:472–477. 3. Centers for Disease Control and Prevention. 2007. Multistate outbreak of Salmonella serotype Tennessee infections associated with peanut butter–United States, 2006–2007. Morb. Mortal. Weekly Rep. 21:56(21):521–524. 4. Centers for Disease Control and Prevention. 2009. Investigation Update: Outbreak of Salmonella Typhimurium Infections, 2008–2009. Available at: http://www.cdc.gov/salmonella/typhimurium/update.html. Accessed 22 February, 2009. 5. D’Aoust, J.Y., D. W. Warburton, and A. M. Sewell. 1985. Salmonella Typhimurium phage-type 10 from cheddar cheese implicated in a major Canadian foodborne outbreak. J. Food Prot. 48:1062–1066. 6. Hohmann, E. L. Nontyphoidal salmonellosis. 2001. Clin. Infect. Dis. 32:263–269. 7. Holliday, S. L., and L. R. Beuchat. 2003. Viability of Salmonella, Escherichia coli O157:H7, and Listeria monocytogenes in yellow fat spreads as affected by storage temperature. J. Food Prot. 66:549–58. 8. Juneja, V. K., and B. S. Eblen. 2000. Heat inactivation of Salmonella Typhimurium DT104 in beef as affected by fat content. Lett. Appl. Microbiol. 30:461–467. CONCLUSIONS Salmonella grows over a wide range of temperatures and will survive long periods of dehydration. As demonstrated in our results, Salmonella and E. coli O157:H7 can survive in contaminated peanut butter stored at room and refrigerated temperatures for long periods of time and therefore, can pose a health risk to consumers. To minimize or eliminate such risks in peanut butter, Food Safety Programs (FSP) should be imposed in peanut butter processing facilities. Such actions would eliminate Salmonella, E. coli O157:H7 or other foodborne pathogens. In addition, plant sanitation and verification of any heat processes are crucial and must be key components of an inclusive FSP to ensure food safety to the public. More research on the survival of foodborne pathogens in peanut butter will be of great importance to the food industry and will translate to fewer recalls of products, recapturing of lost prestige and improvement of the income potential of the food industry. Peanut butter processing fac- NOVEMBER 2009 | FOOD PROTECTION TRENDS

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Food Protection Trends - November 2009

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