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Mexican red salsa is one of the most common side dishes in Mexican cuisine. According to data on foodborne illnesses collected by the Centers for Disease Control and Prevention, salsa was associated with 70 foodborne illness outbreaks between 1990 and 2006. Salsa ingredients such as tomatoes, cilantro, and onions often have been implicated in foodborne illness outbreaks. Mexican-style restaurants commonly prepare a large batch of red salsa, store it at refrigeration temperatures, and then serve it at room temperature. Salmonellais one of the top etiologies in foodborne illness outbreaks associated with salsa, and our preliminary studies revealed the consistent presence of Staphylococcus aureusin restaurant salsa. In the present study, we evaluated the survival of SalmonellaEnteritidis and S. aureusinoculated into restaurant-made salsa samples stored at ambient (20°C) and refrigeration (4°C) temperatures. These test temperature conditions represent best-case and worst-case scenarios in restaurant operations. Salmonellasurvived in all samples stored at room temperature, but S. aureuspopulations significantly decreased after 24 h of storage at room temperature. No enterotoxin was detected in samples inoculated with S. aureusat 6.0 log CFU/g. Both microorganisms survived longer in refrigerated samples than in samples stored at room temperature. Overall, both Salmonellaand S. aureussurvived a sufficient length of time in salsa to pose a food safety risk.

The fates of seeded Escherichia coliO157:H7 and Salmonellaon selected fresh culinary herbs were evaluated at a refrigerated temperature (4°C). Fresh herbs, including cilantro, oregano, basil, chive, parsley, and rosemary, were inoculated with six-strain mixtures of E. coliO157:H7 and Salmonella, and the microbial populations were monitored at 1, 5, 11, 16, 19, and 24 days. For both pathogens, a significant decrease in the population (P< 0.0001) occurred within the first 5 days of storage (<0.8 log). Both pathogens remained the highest on cilantro and the lowest on rosemary (P< 0.0001). Storage time had a significant effect on the survival of E. coliO157:H7; populations declined as storage time progressed. Although storage of cilantro, basil, and chive was terminated after 19 days because of deteriorated quality, significant numbers of both pathogens were recovered from the remaining fresh herbs after 24 days of storage. The results showed that both bacteria were extremely persistent on all test herbs under the test conditions. The results also reinforce the concept that, once contaminated, bacterial pathogens can persist on fresh herbs throughout a normal distribution time.

The efficacy levels of different physical and chemical washing treatments in the reduction of viral and bacterial pathogens from inoculated strawberries were evaluated. Escherichia coliO157:H7, SalmonellaMontevideo, poliovirus 1, and the bacteriophages PRD1, φX174, and MS2 were used as model and surrogate organisms. Chemicals readily available to producers and/or consumers were evaluated as antimicrobial additives for the production of washes. The gentle agitation of contaminated strawberries in water for 2 min led to reductions in microbial populations ranging from 41 to 79% and from 62 to 90% at water temperatures of 22 and 43°C, respectively. Significant reductions (>98%) in numbers of bacteria and viruses were obtained with sodium hypochlorite (50 to 300 ppm of free chlorine), Oxine or Carnebon (200 ppm of product generating “stabilized chlorine dioxide”), Tsunami (100 ppm of peroxyacetic acid), and Alcide (100 or 200 ppm of acidified sodium chlorite) washes. Overall, 200 ppm of acidified sodium chlorite produced the greatest reductions of microorganisms. Hydrogen peroxide (0.5%) was slightly less effective than free chlorine in a strawberry wash and caused slight fruit discoloration. Cetylpyridinium chloride (0.1%) was effective in the reduction of bacterial species, while trisodium phosphate (1%) was effective against viruses. The consumer-oriented produce wash Fit was very effective (>99%) in reducing the numbers of bacteria but not in reducing the numbers of viruses. Another wash, Healthy Harvest, was significantly less effective than Fit in reducing bacterial pathogens but more effective for viruses. The performance of automatic dishwashing detergent was similar to that of Healthy Harvest and significantly better than that of liquid dishwashing detergent. Solutions containing table salt (2% NaCl) or vinegar (10%) reduced the numbers of bacteria by about 90%, whereas only the vinegar wash reduced the numbers of viruses significantly (ca. 95%).

This study compared the effect of different physical and chemical treatments of strawberries and tomatoes to determine their ability to recover seeded viral and bacterial pathogens from produce surfaces. Solutions of salts, amino acids, complex media, and detergents were compared as eluants. Phosphate-buffered saline (PBS) containing 0.1% Tween 80 eluted the highest number of seeded microorganisms. Elution with this defined solution was then compared under different conditions of physical agitation. Rotary shaking for 20 min at 36°C eluted higher numbers of viruses and bacteria than did low- or high-speed stomaching. Commercially available and laboratory prepared bacteriological differential media were compared for their ability to recover and distinguish eluted SalmonellaMontevideo and Escherichia coliO157:H7 strains from seeded produce. The recovery of seeded bacterial pathogens was low when differential media containing selective ingredients were used (Mac-Conkey sorbitol agar, XLD agar, MacConkey agar). Highest recoveries were obtained on a medium consisting of tryptic soy agar supplemented with sodium thiosulfate and ferric ammonium citrate compared with selective media that inhibited up to 50% of the growth of the eluted microorganisms.