A total of 890 samples of fresh produce obtained from Norwegian markets were examined in order to assess the bacteriological quality of the products and their potential public health risk. The samples comprised lettuce, pre-cut salads, growing herbs, parsley and dill, mushrooms and strawberries. The samples were analysed for the presence of thermotolerant coliform bacteria (TCB), Escherichia coli O157, Salmonella spp., Listeria monocytogenes, Staphylococcus spp., and Yersinia enterocolitica. Neither Salmonella spp. nor E. coli O157 were isolated. For all product groups included, TCB were isolated from a small proportion of samples. Three samples harboured L. monocytogenes; one of the isolates belonging to serogroup 1 (champignons) and two of the isolates belonging to serogroup 4 (Chinese leaves and strawberries). Staphylococci were isolated from a relatively large proportion of the samples of strawberries and mushrooms. However, only four isolates were identified as S. aureus (non-toxinogenic). By the use of PCR, the presence of Y. enterocolitica was indicated in a few of the samples of lettuce, whilst no positive samples were found using a culturing method. The study shows that the occurrence of pathogenic bacteria and TCB in the products analysed was quite low. Nevertheless, the results indicate that the type of products analysed may contain pathogenic bacteria and thereby represent a risk to the consumers in regard to food-borne diseases.
A Nordic standard protocol for detection and enumeration of thermotolerant Campylobacter in food has been elaborated (NMKL 119, 3. Ed., 2007). Performance and precision characteristics of this protocol were evaluated in a collaborative study with participation of 14 laboratories from seven European countries. The laboratories performed qualitative, semi-quantitative and quantitative analyses on samples of chicken meat, cut lettuce, and milk artificially inoculated with different concentrations including blank duplicates of one strain of Campylobacter coli (SLV-271) and one strain of Campylobacter jejuni (SLV-542). Expected concentrations (95% C.I.) (cfu g(-1) or ml(-1)) of both strains in matrices were 0.6-1.4 and 23-60 for qualitative detection, and 0.6-1.4; 23-60; and 420-1200 for semi-quantitative detection. For quantitative determination, the expected concentrations of C. jejuni/C. coli were 420-1200/580-1100; 2100-6000/6300-11,000; and 4100-11,000/53,000-97,000 cfu g(-1) or ml(-1). The qualitative and semi-quantitative techniques resulted in comparable detection. The overall specificity and sensitivity of the detection techniques was 98.6% (95% C.I.: 95.1-99.8%) and 82.8% (C.I.: 78.4-86.6%), respectively. The sensitivity was not influenced by food matrix (P=0.359), but was significantly lower for C. coli compared to C. jejuni (P=0.007) and for concentrations below 1.4 cfu g(-1) (P
Many microorganisms (including a number of important foodborne pathogens) can be present on raw fruits and vegetables. Since these products are frequently eaten raw, any pathogens present represent a potential risk to the consumer. The objective of this study was to compare the efficacy of a commercial produce wash with that of water for reducing the total bacterial population on lettuce when used by food service employees in university dining halls. Because this study was carried out in actual food service facilities during their daily operation, we used indigenous produce microflora instead of actual pathogens. Over the course of the study, more than 40 heads of lettuce were divided into thirds, and each section was analyzed for total plate count either before washing, after washing in water, or after washing in Victory produce wash. When initial contamination levels were > or = 100 CFU/g (n = 36 samples), reductions obtained with Victory produce wash (1.8 log CFU/g) were significantly larger (P = 0.0006) than those obtained with water (0.8 log CFU/g). Our results indicate that Victory produce wash is effective in reducing indigenous flora on lettuce during food service preparation. Our results also show that care must be taken in the analysis of microbial reduction data: only a slight reduction in total plate count (ca. 0.1 log CFU/g) and no significant difference in reductions (P = 0.84) were observed when all samples (irrespective of initial contamination level) were compared.
Consumption of minimally-processed, or fresh-cut, fruit and vegetables has rapidly increased in recent years, but there have also been several reported outbreaks associated with the consumption of these products. Sodium hypochlorite is currently the most widespread disinfectant used by fresh-cut industries. Neutral electrolyzed water (NEW) is a novel disinfection system that could represent an alternative to sodium hypochlorite. The aim of the study was to determine whether NEW could replace sodium hypochlorite in the fresh-cut produce industry. The effects of NEW, applied in different concentrations, at different treatment temperatures and for different times, in the reduction of the foodborne pathogens Salmonella, Listeria monocytogenes and Escherichia coli O157:H7 and against the spoilage bacterium Erwinia carotovora were tested in lettuce. Lettuce was artificially inoculated by dipping it in a suspension of the studied pathogens at 10(8), 10(7) or 10(5) cfu ml(-1), depending on the assay. The NEW treatment was always compared with washing with deionized water and with a standard hypochlorite treatment. The effect of inoculum size was also studied. Finally, the effect of NEW on the indigenous microbiota of different packaged fresh-cut products was also determined. The bactericidal activity of diluted NEW (containing approximately 50 ppm of free chlorine, pH 8.60) against E. coli O157:H7, Salmonella, L. innocua and E. carotovora on lettuce was similar to that of chlorinated water (120 ppm of free chlorine) with reductions of 1-2 log units. There were generally no significant differences when treating lettuce with NEW for 1 and 3 min. Neither inoculation dose (10(7) or 10(5) cfu ml(-1)) influenced the bacterial reduction achieved. Treating fresh-cut lettuce, carrot, endive, corn salad and 'Four seasons' salad with NEW 1:5 (containing about 50 ppm of free chlorine) was equally effective as applying chlorinated water at 120 ppm. Microbial reduction depended on the vegetable tested: NEW and sodium hypochlorite treatments were more effective on carrot and endive than on iceberg lettuce, 'Four seasons' salad and corn salad. The reductions of indigenous microbiota were smaller than those obtained with the artificially inoculated bacteria tested (0.5-1.2 log reduction). NEW seems to be a promising disinfection method as it would allow to reduce the amount of free chlorine used for the disinfection of fresh-cut produce by the food industry, as the same microbial reduction as sodium hypochlorite is obtained. This would constitute a safer, 'in situ', and easier to handle way of ensuring food safety.
This is the first report of a major foodborne outbreak of enterohaemorrhagic Escherichia coli (EHEC) in Sweden. It occurred among the nursing staff at a children's hospital with approximately 1600 employees. Contaminated lettuce was the most likely source of infection. Nine persons were culture-positive for Escherichia coli (E. coli) O157 and verocytotoxin-positive by PCR and a further two were verocytotoxin-positive by PCR only. All 11 EHEC-positive individuals had attended a party for approximately 250 staff members, which was held at the hospital. In a questionnaire 37 persons stated that they had symptoms consistent with EHEC infection during the weeks after the party. There was no evidence of secondary transmission from staff to patients. The value of PCR as a sensitive and fast method for diagnosis is discussed in this paper. Pulsed-field gel electrophoresis (PFGE) was used to ascertain that staff members were infected by the same clone, and that two patients with E. coli O157 infection were not.
Produce Safety and Microbiology Research Unit, U.S. Department of Agriculture, Agricultural Research Service, Western Regional Research Center, 800 Buchanan Street, Albany, California 94710, USA. email@example.com
Escherichia coli O157:H7 can survive in low numbers in soil and on plants. Occasionally, conditions may occur in the field that lead to contamination of produce. Survival of enteric pathogens in the field is controlled to a certain extent by complex interactions with indigenous soilborne and seedborne epiphytes. Identifying these interactions may assist in developing strategies to improve produce safety. Two epiphytes were isolated from pathogen-contaminated plants that interact differently with E. coli O157:H7. Wausteria paucula enhanced the survival of E. coli O157:H7 six-fold on lettuce foliage grown from coinoculated lettuce seed. In contrast, Enterobacter asburiae decreased E. coli O157:H7 survival 20- to 30-fold on foliage. Competition also occurred in the rhizosphere and in plant exudate. This competition may be the result of E. asburiae utilization of several of the carbon and nitrogen substrates typically present in exudate and also used by E. coli O157:H7. Hence, competition observed on the plant may involve one or more nutrients provided by the plant. In contrast, a different mechanism may exist between E. coli O157:H7 and W. paucula since commensalism was only observed on foliage, not in the rhizosphere or plant exudate. Good agricultural practices that encourage the growth of competing bacteria, like E. asburiae, may reduce the incidence of produce contamination.
A nationwide outbreak of Salmonella enterica serotypes Newport and Reading occurred between 17 October and 28 November 2008 in Finland. A total of 77 culture-confirmed Salmonella Newport and 30 Salmonella Reading cases, including one case with a double infection, were reported. All strains isolated from the patients were subtyped using serotyping, microbial resistance profiling, and pulsed-field gel electrophoresis (PFGE). Here, the PFGE patterns of the studied Salmonella Newport strains were identical, whereas four different PFGE profiles were found among the Salmonella Reading strains. Two elderly patients died within 2 weeks of the onset of symptoms. Three geographical clusters of cases with an epidemiological link were identified. The traceback investigation suggested that the factor connecting the cases was ready-chopped iceberg lettuce available for mass catering use. However, none of the tested food, environmental samples, or the samples taken from the staff of the processing plant contained Salmonella bacteria. Tracing back to outbreak sources with a short shelf life can be complex.
Access to safe food is a privilege for people living in Iceland. Rapid increase in antimicrobial resistance, related to factory farming and antimicrobial use in agriculture, is a major threat to public health. Increasing food trade between countries and continents facilitates global spread of pathogens and resistance. Icelandic agriculture has benefitted from its isolation and small size. After interventions to reduce the prevalence of Campylobacter and Salmonella at poultry farms, the incidence of human campylobacteriolsis is 17-43/100.000, of which about half is domestically acquired and Salmonella infections 10-15/100.000 mainly acquired abroad. Since Enterohaemorrhagic E. coli (EHEC) has not been detected in domestic cattle, the low incidence of infections is not surprising (0-0.6/100.000/year). A recent outbreak due to a multiresistant EHEC strain was traced to imported lettuce. Antimicrobial use in Icelandic agriculture is among the lowest in Europe and domestic infections caused by Salmonella and Campylobacter are rarely caused by resistant strains. Carbapenemase producing Enterobacteriaceae have not been found in Iceland. Low use of antimicrobials in Icelandic agriculture and actions to limit the spread of Campylobacter and Salmonella have been successful. The public should be informed of the importance of the origin of food and that Icelandic food products are among the safest.