Predicting the Growth of Listeria monocytogenes and Salmonella Typhimurium in Diced Celery, Onions, and Tomatoes during Simulated Commercial Transport, Retail Storage, and Display.

Temperature is arguably the most important factor affecting microbial proliferation in fresh-cut produce. In this study, growth of Listeria monocytogenes in diced onions and celery and Salmonella Typhimurium in diced tomatoes was determined in modified atmosphere packages and snap-fit containers using three fluctuating temperature scenarios for transport, retail storage, and display. As expected, L. monocytogenes growth in diced onions and celery varied depending on the extent of temperature abuse, with exposure to high and intermediate temperature-abuse scenarios generally being growth supportive. A Baranyi primary model with a square-root secondary model for maximum growth rate, and a linear model for maximum population density, were used to estimate Listeria growth under fluctuating temperature. Accuracy and acceptability of the model prediction were evaluated in terms of root mean square error (RMSE) and acceptable prediction zone (APZ), respectively. Overall, growth predictions for L. monocytogenes were more accurate for celery (RMSE, 0.28 to 0.47) than onions (RMSE, 0.42 to 1.53) under the fluctuating temperature scenarios tested. However, both predictions yielded APZ values that ranged from 82 to 100% for celery and 36 to 78% for onions. In contrast, Salmonella Typhimurium populations increased more than 1 log CFU/g in diced tomatoes under the three fluctuating temperature scenarios studied. Overall, these diced products packaged under a high-oxygen atmosphere showed decreased pathogen growth compared with product stored in a passive modified atmosphere. Findings from this study will be particularly useful in assessing the risk associated with consumption of diced celery, tomatoes, and onions and in designing effective packaging strategies to minimize pathogen growth in fresh-cut produce.

Epidemiology of Pseudomonas aeruginosa in agricultural areas.

A prevailing opinion is that the strains of Pseudomonas aeruginosa that infects both plants and humans are two separate species. This study strongly disputes that notion until the modern molecular technology proves otherwise. This paper examines a spectrum of strains occurring in nature, their habitats, dissemination, their relationship to clinical strains, and the environmental conditions that favor their colonization of plants. The isolates were obtained from clinical specimens, plants, soil, and water. The identity of these strains was confirmed using pyocin typing and biochemical assays. The data reveal that agricultural soils, potted ornamental plants, hoses, fountains, and faucets frequently harbored P. aeruginosa. However, it was not commonly found in semi-arid areas, suggesting that moisture and high humidity is necessary for colonization and survival. Though found in soil, P. aeruginosa was seldom isolated on edible plant parts. The pathogenicity of various strains on plants was tested by inoculating vegetables, lettuce slices (Lactuca sativa L. "Great Lakes"), celery stalks (Apium graveolens L. var. Dulce], potato tuber slices (Solanum tuberosum L. "Whiterose"), tomato (Lycopersicon esculentum L. Mill), cucumber (Cucumis sativus L.), rutabaga (Brassica campestris L.), and carrot (Daucus carota L. var sativa). There was considerable variation in the strains' ability to cause rot, but no difference was observed between clinical isolates and others from agricultural fields, water, and soil. Two of the clinical isolates from burn patients, P. aeruginosa PA13 and PA14, exhibited the greatest virulence in causing rot in all the plants that were tested, especially on cucumber, lettuce, potato, and tomato. The study discusses how closely the epidemiology of P. aeruginosa relates to many plant pathogens, and the ability of human isolates to colonize plants and food material under favorable conditions. The biochemical and phenotypic similarity among strains from the clinical and agricultural material is strongly indicative that they are the same species and that plants and soil are natural reservoirs for P. aeruginosa.

Races of the Celery Pathogen Fusarium oxysporum f. sp. apii Are Polyphyletic.

Fusarium oxysporum species complex (FOSC) isolates were obtained from celery with symptoms of Fusarium yellows between 1993 and 2013 primarily in California. Virulence tests and a two-gene dataset from 174 isolates indicated that virulent isolates collected before 2013 were a highly clonal population of F. oxysporum f. sp. apii race 2. In 2013, new highly virulent clonal isolates, designated race 4, were discovered in production fields in Camarillo, California. Long-read Illumina data were used to analyze 16 isolates: six race 2, one of each from races 1, 3, and 4, and seven genetically diverse FOSC that were isolated from symptomatic celery but are nonpathogenic on this host. Analyses of a 10-gene dataset comprising 38 kb indicated that F. oxysporum f. sp. apii is polyphyletic; race 2 is nested within clade 3, whereas the evolutionary origins of races 1, 3, and 4 are within clade 2. Based on 6,898 single nucleotide polymorphisms from the core FOSC genome, race 3 and the new highly virulent race 4 are highly similar with Nei's Da = 0.0019, suggesting that F. oxysporum f. sp. apii race 4 evolved from race 3. Next generation sequences were used to develop PCR primers that allow rapid diagnosis of races 2 and 4 in planta.

Microbiological and Modeling Approach to Derive Performance Objectives for Bacillus cereus Group in Ready-to-Eat Salads.

In this article, the performance objectives (POs) for Bacillus cereus group (BC) in celery, cheese, and spelt added as ingredients in a ready-to-eat mixed spelt salad, packaged under modified atmosphere, were calculated using a Bayesian approach. In order to derive the POs, BC detection and enumeration were performed in nine lots of naturally contaminated ingredients and final product. Moreover, the impact of specific production steps on the BC contamination was quantified. Finally, a sampling plan to verify the ingredient lots' compliance with each PO value at a 95% confidence level (CL) was defined. To calculate the POs, detection results as well as results above the limit of detection but below the limit of quantification (i.e., censored data) were analyzed. The most probable distribution of the censored data was determined and two-dimensional (2D) Monte Carlo simulations were performed. The PO values were calculated to meet a food safety objective of 4 log10 cfu of BC for g of spelt salad at the time of consumption. When BC grows during storage between 0.90 and 1.90 log10 cfu/g, the POs for BC in celery, cheese, and spelt ranged between 1.21 log10 cfu/g for celery and 2.45 log10 cfu/g for spelt. This article represents the first attempt to manage the concept of PO and 2D Monte Carlo simulation in the flow chart of a complex food matrix, including raw and cooked ingredients.

Role of Brushes and Peelers in Removal of Escherichia coli O157:H7 and Salmonella from Produce in Domestic Kitchens.

Consumers are being advised to increase their consumption of fruits and vegetables to reduce their risk of chronic disease. However, to achieve that goal, consumers must be able to implement protocols in their kitchens to reduce their risk of consuming contaminated produce. To address this issue, a study was conducted to monitor the fate of Escherichia coli O157:H7 and Salmonella on produce (cantaloupe, honeydew melon, carrots, and celery) that were subjected to brushing or peeling using common kitchen utensils. Removal of similar levels of Salmonella from carrots was accomplished by peeling and by brushing, but significantly greater removal of E. coli O157:H7 from carrots was accomplished by peeling than by brushing under running water (P < 0.05). Brushing removed significantly fewer pathogens from contaminated cantaloupes than from other produce items (P < 0.05), suggesting that the netted rind provided sites where the pathogen cells could evade the brush bristles. A Sparta polyester brush was less effective than a scouring pad for removing Salmonella from carrots (P < 0.05). In all cases, brushing and peeling failed to eliminate the pathogens from the produce items, which may be the result of contamination of the utensil during use. High incidences of contamination (77 to 92%) were found among peelers used on carrots or celery, the Sparta brush used on carrots, and the scouring pad used on carrots and cantaloupe. Of the utensils investigated, the nylon brush had the lowest incidence of pathogen transference from contaminated produce (0 to 12%). Transfer of pathogens from a potentially contaminated Sparta brush or peeler to uncontaminated carrots did not occur or occurred only on the first of seven carrots processed with the utensil. Therefore, risk of cross-contamination from contaminated utensils to uncontaminated produce may be limited.

Listeria monocytogenes transfer during mechanical dicing of celery and growth during subsequent storage.

The transfer of Listeria monocytogenes to previously uncontaminated product during mechanical dicing of celery and its growth during storage at various temperatures were evaluated. In each of three trials, 275 g of retail celery stalks was immersed in an aqueous five-strain L. monocytogenes cocktail to obtain an average of 5.6 log CFU/g and then was diced using a hand-operated dicer, followed by sequential dicing of 15 identical 250-g batches of uninoculated celery using the same dicer. Each batch of diced celery was examined for numbers of Listeria initially and after 3 and 7 days of storage at 4, 7, and 10 °C. Additionally, the percentage by weight of inoculated product transferred to each of 15 batches of uninoculated celery was determined using inoculated red stems of Swiss chard as a surrogate. Listeria transfer to diced celery was also assessed after removing the Swiss chard. L. monocytogenes transferred from the initial batch of inoculated celery to all 15 batches of uninoculated celery during dicing, with populations decreasing from 5.2 to 2.0 log CFU/g on the day of processing. At 10 °C, Listeria reached an average population of 3.4 log CFU/g in all batches of uninoculated celery. Fewer batches of celery showed significant growth during storage at 4 and 7 °C (P < 0.05). Swiss chard pieces were recovered from all 15 batches of celery, with similar amounts seen in batches 2 to 15 (P > 0.05). L. monocytogenes was also recovered from each batch of uninoculated celery after the removal of Swiss chard, with populations decreasing from 4.7 to 1.7 log CFU/g. Storing the diced celery at 10 °C yielded a L. monocytogenes generation time of 0.87 days, with no significant growth observed during storage at 4 or 7 °C. Consequently, mitigation strategies during dicing and proper refrigeration are essential to minimizing potential health risks associated with diced celery.

Association of 'Candidatus Liberibacter solanacearum' with a vegetative disorder of celery in Spain and development of a real-time PCR method for its detection.

A new symptomatology was observed in celery (Apium graveolens) in Villena, Spain in 2008. Symptomatology included an abnormal amount of shoots per plant and curled stems. These vegetative disorders were associated with 'Candidatus Liberibacter solanacearum' and not with phytoplasmas. Samples from plant sap were immobilized on membranes based on the spot procedure and tested using a newly developed real-time polymerase chain reaction assay to detect 'Ca. L. solanacearum'. Then, a test kit was developed and validated by intralaboratory assays with an accuracy of 100%. Bacterial-like cells with typical morphology of 'Ca. Liberibacter' were observed using electron microscopy in celery plant tissues. A fifth haplotype of 'Ca. L. solanacearum', named E, was identified in celery and in carrot after analyzing partial sequences of 16S and 50S ribosomal RNA genes. From our results, celery (family Apiaceae) can be listed as a new natural host of this emerging bacterium.

The effect of pre-treatment and modified atmosphere packaging on contents of phenolic compounds and sensory and microbiological quality of shredded celeriac.

BACKGROUND: The aim of this study was to determine the effect of washing (4 °C, 120 s) or soaking (4 °C, 600 s) of shredded celeriac in tap water on changes in contents of phenolic compounds, including furanocoumarins, and sensory and microbiological quality during 12 days of storage. The product was packaged in air or modified atmosphere containing 2/10/88 kPa O2/CO2/N2. RESULTS: The applied pre-treatment consisting of washing or soaking of shredded celeriac in water resulted in decreases in 8-methoxypsoralen content by approximately 50 and 70% respectively and phenolic content by 30% compared with samples that were not subjected to pre-treatment. During storage of shredded celeriac, a further significant (P ≤ 0.05) reduction in phenolic compounds and an approximately 2.5-fold increase in the total content of furanocoumarins were found. The application of modified atmosphere packaging had a significant effect on the maintenance of good sensory and microbiological quality of the tested product. CONCLUSION: Modified atmosphere packaging of shredded celeriac not subjected to pre-treatment made it possible to obtain a product with good sensory and microbiological quality and the highest content of phenolic compounds. The level of furanocoumarins recorded in the tested product does not constitute a health hazard.

Fate of Escherichia coli O157:H7, Listeria monocytogenes, and Salmonella on fresh-cut celery.

Illnesses from Escherichia coli O157:H7, Listeria monocytogenes, and Salmonella have been associated with the consumption of numerous produce items. Little is known about the effect of consumer handling practices on the fate of these pathogens on celery. The objective of this study was to determine pathogen behavior at different temperatures under different storage conditions. Commercial fresh-cut celery was inoculated at ca. 3logCFU/g onto either freshly cut or outer uncut surfaces and stored in either sealed polyethylene bags or closed containers. Samples were enumerated following storage for 0, 1, 3, 5, and 7 days when held at 4 °C or 12 °C, and after 0, 8, and 17 h, and 1, and 2 days when held at 22 °C. At 4 °C, all populations declined by 0.5-1.0logCFU/g over 7 days. At 12 °C, E. coli O157:H7 and Salmonella populations did not change, while L. monocytogenes populations increased by ca. 0.5logCFU/g over 7 days. At 22 °C, E. coli O157:H7, Salmonella, and L. monocytogenes populations increased by ca. 1, 2, or 0.3logCFU/g, respectively, with the majority of growth occurring during the first 17 h. On occasion, populations on cut surfaces were significantly higher than those on uncut surfaces. Results indicate that populations are reduced under refrigeration, but survive and may grow at elevated temperatures.

Hospital-acquired listeriosis outbreak caused by contaminated diced celery--Texas, 2010.

BACKGROUND: Listeria monocytogenes causes often-fatal infections affecting mainly immunocompromised persons. Sources of hospital-acquired listeriosis outbreaks can be difficult to identify. We investigated a listeriosis outbreak spanning 7 months and involving 5 hospitals. METHODS: Outbreak-related cases were identified by pulsed-field gel electrophoresis (PFGE) and confirmed by multiple-locus variable-number tandem-repeat analysis (MLVA). We conducted patient interviews, medical records reviews, and hospital food source evaluations. Food and environmental specimens were collected at a hospital (hospital A) where 6 patients had been admitted before listeriosis onset; these specimens were tested by culture, polymerase chain reaction (PCR), and PFGE. We collected and tested food and environmental samples at the implicated processing facility. RESULTS: Ten outbreak-related patients were immunocompromised by ≥1 underlying conditions or treatments; 5 died. All patients had been admitted to or visited an acute-care hospital during their possible incubation periods. The outbreak strain of L. monocytogenes was isolated from chicken salad and its diced celery ingredient at hospital A, and in 19 of >200 swabs of multiple surfaces and in 8 of 11 diced celery products at the processing plant. PCR testing detected Listeria in only 3 of 10 environmental and food samples from which it was isolated by culturing. The facility was closed, products were recalled, and the outbreak ended. CONCLUSIONS: Contaminated diced celery caused a baffling, lengthy outbreak of hospital-acquired listeriosis. PCR testing often failed to detect the pathogen, suggesting its reliability should be further evaluated. Listeriosis risk should be considered in fresh produce selections for immunocompromised patients.

CorA, the magnesium/nickel/cobalt transporter, affects virulence and extracellular enzyme production in the soft rot pathogen Pectobacterium carotovorum.

Pectobacterium carotovorum (formerly Erwinia carotovora ssp. carotovora) is a phytopathogenic bacterium that causes soft rot disease, characterized by water-soaked soft decay, resulting from the action of cell wall-degrading exoenzymes secreted by the pathogen. Virulence in soft rot bacteria is regulated by environmental factors, host and bacterial chemical signals, and a network of global and gene-specific bacterial regulators. We isolated a mini-Tn5 mutant of P. carotovorum that is reduced in the production of extracellular pectate lyase, protease, polygalacturonase and cellulase. The mutant is also decreased in virulence as it macerates less host tissues than its parent and is severely impaired in multiplication in planta. The inactivated gene responsible for the reduced virulent phenotype was identified as corA. CorA, a magnesium/nickel/cobalt membrane transporter, is the primary magnesium transporter for many bacteria. Compared with the parent, the CorA(-) mutant is cobalt resistant. The mutant phenotype was confirmed in parental strain P. carotovorum by marker exchange inactivation of corA. A functional corA(+) DNA from P. carotovorum restored exoenzyme production and pathogenicity to the mutants. The P. carotovorum corA(+) clone also restored motility and cobalt sensitivity to a CorA(-) mutant of Salmonella enterica. These data indicate that CorA is required for exoenzyme production and virulence in P. carotovorum.

Response surface methodology-based optimization of decontamination conditions for Escherichia coli O157:H7 and Salmonella Typhimurium on fresh-cut celery using thermoultrasound and calcium propionate.

A combination of thermoultrasound (temperature: 50, 55, 60°C; time: 10, 15, 20 min with the frequency of 40 KHz) and calcium propionate (concentration: 1, 2, 3%, w/v) treatment was applied to decontaminate Escherichia coli O157:H7 and Salmonella enterica serovar Typhimurium (S. Typhimurium) from fresh-cut celery. Using a Box-Behnken experimental design, predictive quadratic equations were developed for treatment-based population reductions of E. coli O157:H7 (R(2)=0.98, p<0.001) and S. Typhimurium (R(2)=0.96, p<0.001), and verified using 10 randomly selected treatment conditions. Among three factors (temperature, time, and calcium propionate concentration), temperature represented higher significance for inactivation of pathogenic bacteria. No significant changes (p>0.05) were observed in the color and shear force resistance of the treated celery. The optimum treatment conditions were 60°C thermoultrasound with 2% calcium propionate for 15 min (E. coli O157:H7) and 59°C thermoultrasound with 2% calcium propionate for 17 min (S. Typhimurium). Scanning electron microscopy was used to confirm membrane disruption in the treated microbial cells in each optimal condition. The combined treatment of thermoultrasound and calcium propionate contributes to the effective inactivation (more than 5 log reduction) of E. coli O157:H7 and S. Typhimurium on fresh-cut celery. Furthermore, this treatment extends fresh storability without physical quality deterioration.

Pyrene biodegradation in an industrial soil exposed to simulated rhizodeposition: how does it affect functional microbial abundance?

Rhizodeposition is an important biogeochemical process for the phytoremediation of contaminated substrates. This study investigated the effects of various rhizodeposition components from celery (Apium graveolens) on pyrene biodegradation and microbial abundance in a long-term contaminated soil. Batch microcosms simulating in situ contaminated soil were amended with lipophilic extract, water-soluble extract, or debris from celery root to mimic plant rhizodeposition within 70 days. Soil was intermittently analyzed for pyrene concentration and target gene abundance estimated by real-time PCR. Lipophilic extract was the major simulated rhizodeposit enhancing pyrene biodegradation, while water-soluble extract stimulated microbial growth most efficiently. The relative abundance of total polycyclic aromatic hydrocarbon (PAH) degraders was enhanced by lipophilic extract but inhibited by the other two rhizodeposits, indicating that these components exerted different selective pressures on PAH degrader community. Moreover, PAH catabolic pathway may involve in the pollutant detoxification and fatty acid metabolism by microorganisms, which were also affected by rhizodeposition. These results provide insights into plant-microbe interactions responsible for PAH biodegradation and offer opportunities to facilitate PAH phytoremediation in industrial sites.

Regulation of motility in Erwinia carotovora subsp. carotovora: quorum-sensing signal controls FlhDC, the global regulator of flagellar and exoprotein genes, by modulating the production of RsmA, an RNA-binding protein.

Erwinia carotovora subsp. carotovora causes soft-rotting (tissue-macerating) disease in many plants and plant organs. Although pectinases are the primary determinants of virulence, several ancillary factors that augment bacterial virulence have also been identified. One such factor is bacterial motility. Flagellum formation and bacterial movement are regulated in many enterobacteria, including E. carotovora subsp. carotovora, by FlhDC, the master regulator of flagellar genes and FliA, a flagellum-specific σ factor. We document here that motility of E. carotovora subsp. carotovora is positively regulated by the quorum-sensing signal, N-acylhomoserine lactone (AHL), and negatively regulated by RsmA, a post-transcriptional regulator. RsmA, an RNA-binding protein, causes translational repression and promotes RNA decay. Our data show that RsmA negatively regulates flhDC and fliA expression. Moreover, the chemical stabilities of transcripts of these genes are greater in an RsmA- mutant than in RsmA+ bacteria. These observations contrast with positive regulation of flhDC and motility by CsrA (=RsmA) in Escherichia coli. In the absence of AHL, the AHL receptors ExpR1/ExpR2 (=AhlR) in Erwinia carotovora subsp. carotovora negatively regulate motility and expression of flhDC and fliA by activating RsmA production. In the presence of AHL, regulatory effects of ExpR1/ExpR2 are neutralized, resulting in reduced levels of rsmA expression and enhanced motility.

Carvacrol and cinnamaldehyde inactivate antibiotic-resistant Salmonella enterica in buffer and on celery and oysters.

The emergence of antibiotic-resistant Salmonella is of concern to food processors. The objective of this research was to identify antimicrobial activities of cinnamaldehyde and carvacrol against antibiotic-resistant Salmonella enterica in phosphate-buffered saline (PBS) and on celery and oysters. Twenty-three isolates were screened for resistance to seven antibiotics. Two resistant and two susceptible strains were chosen for the study. S. enterica cultures (10(5) CFU/ml) were added to different concentrations of cinnamaldehyde and carvacrol (0.1, 0.2, 0.3, and 0.4% [vol/vol]) in PBS, mixed, and incubated at 37 degrees C. Samples were taken at 0, 1, 5, and 24 h for enumeration. Celery and oysters were inoculated with S. enterica (10(6-7) CFU/ml), treated with 1% cinnamaldehyde or 1% carvacrol, incubated at 4 degrees C, and then sampled for enumeration on days 0 and 3. Both antimicrobials induced complete inactivation of S. enterica in PBS at 0.3 and 0.4% on exposure, and on 0.2% in 1 h. Exposure to cinnamaldehyde at 0.1% inactivated all pathogens at 1 h, and survivors were observed only for Salmonella Newport with 0.1% carvacrol at 1 h. In celery, 1% carvacrol reduced S. enterica populations to below detection on day 0, while 1% cinnamaldehyde reduced populations by 1 and 2.3 log on day 0 and day 3, respectively. In oysters, both antimicrobials caused about 5-log reductions on day 3. These results show the potential antimicrobial effects of carvacrol and cinnamaldehyde against antibiotic-resistant S. enterica in vitro and in foods.

Endophytic fungi occurring in fennel, lettuce, chicory, and celery--commercial crops in southern Italy.

The occurrence of endophytic fungi in fennel, lettuce, chicory, and celery crops was investigated in southern Italy. A total of 186 symptomless plants was randomly collected and sampled at the stage of commercial ripeness. Fungal species of Acremonium, Alternaria, Fusarium, and Plectosporium were detected in all four crops; Plectosporium tabacinum was the most common in all crop species and surveyed sites. The effect of eight endophytic isolates (five belonging to Plectosporium tabacinum and three to three species of Acremonium) inoculated on lettuce plants grown in gnotobiosis was assessed by recording plant height, root length and dry weight, collar diameter, root necrosis, and leaf yellowing. P. tabacinum and three species of Acremonium, inoculated on gnotobiotically grown lettuce plants, showed pathogenic activity that varied with the fungal isolate. Lettuce plants inoculated with the isolates Ak of Acremonium kiliense, Ac of Acremonium cucurbitacearum, and P35 of P. tabacinum showed an increased root growth, compared to the non-inoculated control. The high frequency of P. tabacinum isolation recorded in lettuce plants collected in Bari and Metaponto, and in fennel plants from Foggia agricultural districts, suggests a relationship not only between a crop species and P. tabacinum, but also between the occurrence of the endophyte and the crop rotation history of the soil.

Host range of Cercospora apii and C. beticola and description of C. apiicola, a novel species from celery.

The genus Cercospora is one of the largest and most heterogeneous genera of hyphomycetes. Cercospora species are distributed worldwide and cause Cercospora leaf spot on most of the major plant families. Numerous species described from diverse hosts and locations are morphologically indistinguishable from C. apii and subsequently are referred to as C. apii sensu lato. The importance and ecological role that different hosts play in taxon delimitation and recognition within this complex remains unclear. It has been shown that Cercospora leaf spot on celery and sugar beet are caused respectively by C. apii and C. beticola, both of which are part of the C. apii complex. During this study we characterized a new Cercospora species, C. apiicola, which was isolated from celery in Venezuela, Korea and Greece. The phylogenetic relationship between C. apiicola and other closely related Cercospora species was studied with five different gene areas. These analyses revealed that the C. apiicola isolates cluster together in a well defined clade. Both C. apii and C. beticola sensu stricto form well defined clades and are shown to have wider host ranges and to represent distinct species.

Elevated temperature enhances virulence of Erwinia carotovora subsp. carotovora strain EC153 to plants and stimulates production of the quorum sensing signal, N-acyl homoserine lactone, and extracellular proteins.

Erwinia carotovora subsp. atroseptica, E. carotovora subsp. betavasculorum, and E. carotovora subsp. carotovora produce high levels of extracellular enzymes, such as pectate lyase (Pel), polygalacturonase (Peh), cellulase (Cel), and protease (Prt), and the quorum-sensing signal N-acyl-homoserine lactone (AHL) at 28 degrees C. However, the production of these enzymes and AHL by these bacteria is severely inhibited during growth at elevated temperatures (31.2 degrees C for E. carotovora subsp. atroseptica and 34.5 degrees C for E. carotovora subsp. betavasculorum and most E. carotovora subsp. carotovora strains). At elevated temperatures these bacteria produce high levels of RsmA, an RNA binding protein that promotes RNA decay. E. carotovora subsp. carotovora strain EC153 is an exception in that it produces higher levels of Pel, Peh, Cel, and Prt at 34.5 degrees C than at 28 degrees C. EC153 also causes extensive maceration of celery petioles and Chinese cabbage leaves at 34.5 degrees C, which correlates with a higher growth rate and higher levels of rRNA and AHL. The lack of pectinase production by E. carotovora subsp. carotovora strain Ecc71 at 34.5 degrees C limits the growth of this organism in plant tissues and consequently impairs its ability to cause tissue maceration. Comparative studies with ahlI (the gene encoding a putative AHL synthase), pel-1, and peh-1 transcripts documented that at 34.5 degrees C the RNAs are more stable in EC153 than in Ecc71. Our data reveal that overall metabolic activity, AHL levels, and mRNA stability are responsible for the higher levels of extracellular protein production and the enhanced virulence of EC153 at 34.5 degrees C compared to 28 degrees C.

Effect of gamma irradiation on the microbiological quality of minimally processed vegetables.

The initial microflora of minimally processed celery and cabbage packaged under a modified atmosphere was determined. The samples came from the same producer and were sold in a supermarket chain of Santiago, Chile. Although neither E. coli nor Salmonella spp. were detected, initial total plate and Enterobacteriaceae counts were high (= 10(5) cfu/g), not meeting in most cases the specifications of the Chilean legislation. The D10 value for two strains of E. coli (ATCC 8739 and a wild type) inoculated as indicator microorganisms was determined. After irradiating with 5 D10 doses (1kGy), the variation of the microbial population and sensory quality during a 7 days storage period at 5 degrees C was studied. In irradiated celery, a reduction of 4.7 and 3.8 logs for total plate and Enterobacteriaceae counts respectively was observed. There was a decrease of 3.8 and 3.6 logs in cabbage for total plate and Enterobacteriaceae counts respectively. In both irradiated and non-irradiated vegetables, neither E. coli nor Salmonella spp. were detected. An increase of 1.6 - 1.7 logs in both microbiological parameters in non-irradiated samples was observed during storage. In irradiated products, only celery showed an increase of 1.2 log in total plate count. Both Enterobacteriaceae count in the two vegetables and Total plate count in cabbage presented essentially no variation in time. No significant differences (p = 0.05) were detected in sensory total quality between the control and the irradiated vegetable and between days of storage.

Effectiveness and residues of procymidone applied on celery and fennel in the control of Sclerotinia sclerotiorum (Lib.) de Bary.

A biennial experimentation has been led using the active ingredient (a.i.) procymidone, for the control of Sclerotinia sclerotiorum (Lib.) De Bary on fennel and celery. At present this utilizathion it is not authorized, even though this "minor use" is considered essential for the control of the various phytopathologies. For every test, both in field and in greenhouse, two treatments to the dose of 40 g/hl of a.i. have been made. After the second treatment two assessments were led to check effectiveness of a.i. and subsequent vegetable samplings have been made to determine the entity and the persistence of the residues of the used active ingredient. At the end of the agricultural cycle, in all the tests a good control of the infection caused by the fungus has been found; statistically significant differences of the infection between treated plots and the control. At harvesting (21 days from the 2nd treatment) we have found a residue average value of 0.1-0.2 mg/kg (field) and 0.3-0.4 mg/kg (greenhouse) on fennel and of: 1.0-1.5 mg/kg (field) e 3.0-3.5 mg/kg (greenhouse) on celery.