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Listeria monocytogenesis a foodborne pathogen associated with fresh produce vectors such as leafy greens. Recent outbreaks and recalls associated with red cabbage–containing salads have brought attention to this food commodity. Although data on the proliferation of L. monocytogenesare available for different varieties of whole and cut white cabbage, no information is available on the fate of this pathogen on red cabbage. The aim of this study was therefore to explore the survival of L. monocytogeneson cut red cabbage (Brassica oleraceaL. var. capitataf. rubra) during storage at different temperatures. Red cabbage was cut into pieces (5 by 4 cm) and spot inoculated with a six-strain cocktail of rifampin-resistant L. monocytogenes,resulting in an initial inoculation level of 4 log CFU/g. Samples were stored at 5 or 10°C for 14 days or at 25°C for 7 days. At intervals during storage, L. monocytogeneswas enumerated by homogenization of cabbage with Butterfield's phosphate buffer, and serial dilutions were plated onto brain heart infusion agar supplemented with rifampin. No growth of L. monocytogeneswas observed on cut red cabbage during storage at 5°C, and only minimal proliferation was observed at the higher temperatures. Significant population increases of 0.58 and 1.07 log CFU/g were determined after 3 days of storage at 10 and 25°C, respectively; however, a significant decrease of 0.77 log CFU/g from 3 to 14 days was also observed at 10°C. The modeled growth rates for L. monocytogeneson cut red cabbage stored at 5 and 10°C were 0.11±0.03 and 0.27±0.07 log CFU/g/day, with calculated times to a 1-log CFU/g increase of 9.51 and 3.70 days, respectively; however, L. monocytogenesdid not achieve a 1-log increase at either temperature in this study. At 25°C, the modeled growth rate of L. monocytogeneson cut red cabbage was 1.15±0.36 log CFU/g, leading to a calculated and an observed 1-log increase in 0.87 and 3.00 days, respectively. Results from this study aid in understanding the fate of L. monocytogeneson cut red cabbage during storage at different temperatures.

•S. entericaremained relatively stable during the storage of silica and litter carriers.•E. faeciumreduced in population in all carriers during 120-day storage.•The silica carrier was chosen to dry-inoculate S. entericaonto peaches.•S. entericaremained stable on dry-inoculated orchard peaches during 28-day storage.•Mode of inoculation influences S. entericasurvival on retail and orchard peaches.

Salmonella entericais well known for its ability to survive and persist in low-moisture environments. Previous studies have indicated a link between the initial cell level and the population of Salmonellathat survives after desiccation and subsequent storage; however, how the initial cell concentration affects survival is unknown. This study was conducted to examine this phenomenon and to determine whether it occurs in other microorganisms, specifically Shiga toxigenic Escherichia coli(STEC) and Enterococcus faecium. Salmonella,STEC, and E. faeciumwere grown as sessile cells on Trypticase soy agar with yeast extract (TSAYE) and harvested in buffered peptone water (BPW). To determine recovery at different initial cell levels, cultures were diluted to 9, 7, and 5 log CFU/mL and applied to filters. Filters were dried for 24 h and then stored for 28 days at 25°C and 33% relative humidity. During storage, cells were recovered from filters with BPW and cultivated on TSAYE. Recovery of both Salmonellaand E. coli,but not E. faecium,was nonproportional. Lower initial populations were less viable after 24 h of desiccation; ≥10 log CFU/mL was recovered when 11 log CFU/mL was desiccated, but <3 log CFU/mL was recovered when 5 log CFU/mL was desiccated. Once dried, persistence did not appear affected by initial cell concentration. When inactivated (heat-treated) cells were added to the diluent, recovery of Salmonellawas proportional with respect to the initial cell level. To further examine the response to desiccation, Salmonellawas diluted in BPW containing 1 of 11 test cell components related to quorum sensing or known to affect desiccation resistance to assess recovery and persistence. Of the 11 additions, only cell debris fractions, cell-free extract, and peptidoglycan improved recovery of Salmonella. Desiccation survival appears related to cell wall components; however, the exact mechanism affecting survival remains unknown.

Growth on solid media as sessile cells is believed to increase the desiccation tolerance of Salmonella enterica. However, the reasons behind increased resistance have not been well explored. In addition, the same effect has not been examined for other foodborne pathogens such as pathogenic Escherichia colior Listeria monocytogenes. The purpose of this research was twofold: first, to determine the role of oxygenation during growth on the desiccation resistance of S. enterica, E. coli,and L. monocytogenes, and second, to determine the effect of sessile versus planktonic growth on the desiccation resistance of these pathogens. Three different serotypes each of Salmonella, E. coli,and L. monocytogeneswere cultured in Trypticase soy broth with 0.6% yeast extract (TSBYE), with (aerobic) shaking or on TSBYE with agar under either aerobic or anaerobic conditions and harvested in the stationary phase. After adding cell suspensions to cellulose filter disks, pathogen survival was determined by enumeration before drying (0 h) and after drying for 24 h. Results showed statistical differences in harvested initial populations before drying. For Salmonella,a correlation was found between high initial population and greater survival on desiccation (P= 0.05). In addition, statistical differences (P≤ 0.05) between survival based on growth type were identified. However, differences found were not the same for the three pathogens, or between their serotypes. In general, Salmonellaand E. colidesiccation resistance followed the pattern of aerobic agar media ≥ liquid media ≥ anaerobic agar media. For L. monocytogenesserotypes, resistance to desiccation was not statistically different based on mode of growth. These results indicate growth on solid media under aerobic conditions is not always necessary for optimal desiccation survival, but may be beneficial when the desiccation resistance of the test serotype is unknown.

Environmental monitoring for Listeria monocytogenesin food processing environments is key for ensuring the safety of ready-to-eat foods. For sampling, swabs are often hydrated with a wetting or transport medium that may contain neutralizers and other ingredients. After swabbing the environment, the swabs may then be transported or shipped cold to an off-site laboratory for testing, ideally within 48 h. Extended shipping times may subject the pathogen to increased temperatures in the presence of the wetting medium, organics, and other chemicals from the processing facility that could confound detection. This study evaluated growth and detection of L. monocytogeneson stainless steel exposed to either buffer or sodium hypochlorite before drying. Swabs were rehydrated with Butterfield's phosphate buffer, neutralizing buffer, Letheen broth, or Dey-Engley neutralizing broth before swabbing. Swabs were stored in the presence of no added food, cheese whey, or ice cream under both optimal (4°C) and suboptimal (15°C) temperatures for up to 72 h. Overall, there was no growth of L. monocytogenesat 4°C through 72 h of storage, although enrichment from these swabs was dependent on the presence and type of food matrix. Pathogen growth during storage at 15°C was more variable and depended on both the food matrix and transport media used, with Dey-Engley and Letheen broths allowing for the highest population increases. Overall, more enrichments resulting in L. monocytogenesdetections were observed when using Letheen broth and neutralizing buffer than Dey-Engley broth, which resulted in fewer detections at 15°C. Logistic regression and Cochran-Mantel-Haenszel analyses determined that storage temperature, transport media, and food matrix all significantly affected detection of L. monocytogenes,whereas storage time did not have a clear effect on recovery from swabs.

•L. monocytogenespersisted on IQF vegetables for 12 mo with minimal reduction.•No difference in survival between L. monocytogeneslineages was observed.•L. monocytogenessurvival was similar at the two tested temperatures, −18 and −10°C.

Cheeses made with unpasteurized milk are a safety concern due to possible contamination with foodborne pathogens. Listeria monocytogenesand Escherichia coliO157:H7 have been implicated in several outbreaks and recalls linked to Gouda cheese made with unpasteurized milk. The U.S. Food and Drug Administration Code of Federal Regulations requires cheeses made with unpasteurized milk to be aged at a minimum of 1.7°C for at least 60 days before entering interstate commerce. The goal of this study was (i) to assess the population dynamics of L. monocytogenesand E. coliO157:H7 during aging of Gouda cheese when the pathogens were inoculated into the unpasteurized milk used for manufacture and (ii) to compare the native microbial populations throughout manufacture and aging. Unpasteurized milk was inoculated with L. monocytogenesat 1 or 3 log CFU/mL or with E. coliO157:H7 at 1 log CFU/mL, and Gouda cheese was manufactured in laboratory-scale or pilot plant–scale settings. Cheeses were stored at 10°C for at least 90 days, and some cheeses were stored up to 163 days. Initial native microflora populations in unpasteurized milk did not differ significantly for laboratory-scale or pilot plant–scale trials, and population dynamics trended similarly throughout cheese manufacture and aging. During manufacture, approximately 81% of the total L. monocytogenesand E. coliO157:H7 populations was found in the curd samples. At an inoculation level of 1 log CFU/mL, L. monocytogenessurvived in the cheese beyond 60 days in four of five trials. In contrast, E. coliO157:H7 was detected beyond 60 days in only one trial. At the higher 3-log inoculation level, the population of L. monocytogenesincreased significantly from 3.96±0.07 log CFU/g at the beginning of aging to 6.00±0.73 log CFU/g after 150 days, corresponding to a growth rate of 0.04±0.02 log CFU/g/day. The types of native microflora assessed included Enterobacteriaceae,lactic acid bacteria, mesophilic bacteria, and yeasts and molds. Generally, lactic acid and mesophilic bacterial populations remained consistent at approximately 8 to 9 log CFU/g during aging, whereas yeast and mold populations steadily increased. The data from this study will contribute to knowledge about survival of these pathogens during Gouda cheese production and will help researchers assess the risks of illness from consumption of Gouda cheese made with unpasteurized milk.

•Both pathogens survived on all cooked vegetables stored at 5°C.•L. monocytogenes did not grow on cooked pepper stored at 10°C.•Both pathogens exhibited higher growth rates as the storage temperature increased.•The highest growth rates of both pathogens were estimated on cooked carrot at 25°C.•Growth rates of S. entericawere higher than L. monocytogenesat 25°C.