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WETLAND SEPTIC SYSTEMS
Results of a study of health hazards of consuming fruits and vegetables that may contain contaminants produced from irrigation with septic effluent.
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At our home page on this topic, SEWAGE CONTAMINANTS in FRUIT / VEGETABLES, we pose a series of questions regarding the article below, and we suggest some follow-up research. We also express an opinion about the comparative pathogenic contamination risks identified by this research article and the risks likely to be faced by growing fruits or vegetables over or near septic drainfields.
Readers should also see our safe-planting discussion at Gardens Near Septics and see our discussion of pathogens in sewage at SEWAGE PATHOGENS in SEPTIC SLUDGE: what makes up the contents of residential sewage? and also SEWAGE NITROGEN CONTAMINANTS - a second important type of septic effluent contamination.
The authors obtained 50 vegetable samples from various regions in Morocco and examined them to determine the micro biological quality of these products. Aerobic count, coliform, enterococci, and Staphylococcus areus were evaluated. This analysis revealed high levels of enterococci, fecal coliforms, and total coliforms. No coagulase-positive Staphylococcus aureas was detected in any of the samples analyzed.
Biochemical identification of Enterobacteriaceae showed the presence of Citrobacter freundii (28 percent), Enterobacter cloacae (27 percent), Escherichia coli (16 percent), Enterobacter sakazakii (12 percent), Klebsiella pneamoniae (17 percent), Serratia liquefaciens (11 percent), and Salmonella arizonae (0.7 percent). The results clearly demonstrate that vegetables irrigated with untreated wastewater have a high level of microbiological contamination. Consequently, these vegetables may be a threat for the Moroccan consumer and may be considered a serious risk to Moroccan public health.
No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (See the original article citation in the Journal of Environmental Health, June 2007 listed above and at the end of this page.)
SEPTIC SYSTEMS - INTRODUCTION
An increase in consumption of fresh fruits and vegetables worldwide has been paralleled by an increase in the number of foodborne illnesses attributed to fresh products. Numerous reports have indicated that raw vegetables may harbor potential foodborne pathogens (Beuchat, 1996). In particular, tomatoes, cantaloupes, and sprouts have been linked to outbreaks of salmonellosis (Guo, Chen, Brackett, & Beuchat, 2001), and outbreaks of illnesses caused by Escherichia coli O157:H7 have been associated with melon, apple cider, lettuce, and radish sprouts (Breuer et al., 2001). Moreover, coleslaw, cabbage, potatoes, radishes, bean sprouts, and cucumbers contaminated with Listeria monocytogenes have been linked to disease outbreaks (Shearer, Strapp, & Joerger, 2001), and salad vegetables also may be contaminated with Campylobacter (Evans, Ribeiro, & Salmon, 2003).
In Morocco, vegetable products have been in great demand in recent years. Since the rate of precipitation has been very low during these last decades, wastewater is increasingly being used in agriculture. Little information is available on the number of human foodborne-illness outbreaks that have occurred from consumption of raw vegetables. The use of raw sewage to irrigate crops is an important mechanism that helps to propagate conditions conducive to cholera and typhoid fever (Castro-Rosas & Escartin, 2000). Increases in foodborne illnesses during the summer are not fully understood, although fresh produce likely plays a role since it is consumed in higher quantities during the summer.
Materials and Methods
A total of 50 vegetable samples were procured for bacteriological examination. Vegetables of various types were obtained from several wastewater-irrigated agricultural regions in Morocco. Sampling was conducted from August 2002 to July 2004. The vegetable samples were collected in sterile polyethylene bags, and steps were taken to avoid contamination of the vegetables by soil or other contamination sources. Each sample was collected in triplicate to prevent sampling error. The vegetables were tomato, radish, cucumber, eggplant, potato, pepper, garden pea, gourd, zucchini, artichoke, broad bean, turnip, onion, French bean, and lettuce.
Vegetables of various types were obtained from several wastewater-irrigated agricultural regions in Morocco. Sampling was conducted from August 2002 to July 2004. The vegetable samples were collected in sterile polyethylene bags, and steps were taken to avoid contamination of the vegetables by soil or other contamination sources. Each sample was collected in triplicate to prevent sampling error. The vegetables were tomato, radish, cucumber, eggplant, potato, pepper,
All the samples were transported to the laboratory under low temperature (<7[degrees]C) and stored at 4[degrees]C until testing. They were analyzed within 20 hours of sampling. Each sample was rinsed several times with sterile distilled water to eliminate the soil. Before analysis, 25 g of each sample was homogenized for two minutes with 225 mL of 0.1 percent sterilepeptone water with a Model 400 Stomacher (Seward Medical, London) and serially diluted.
Using the spread-plate technique and 100 [micro]L from the serial dilution, the authors prepared duplicate plates for the determination of aerobic plate counts (APC) Enterobactericiceae, fecal coliforms, total colilorms, Staphylococcus,and Streptococcus.
Typical colonies were round, red to pink, 0.5 to 2 mm in diameter, and surrounded with a red-to-pink halo. Staphlococcus aureus counts were determined with Baird-Parker Agar (Difco) with egg yolk--tellurite emulsion, and plates were incubated at 37[degrees]C for 24 hours to 48 hours. Colonies selected from the agar surface were examined under microscope for Gram stain and were tested for catalase reaction and then for coagulase activity with plasma rabbit (Biokar).
To isolate Salmonella spp., we pummeled a 25-g sample in a stomacher with 225 mL of buffered peptone water and pre-enriched the homogenate 37[degrees]C for 18 hours. A 100-[micro]L sample was subcultured into 10 mL of Rappaport Vassiliadis Broth (Difco) and enriched at 41.5[degrees]C for 24 hours and 48 hours. One mL of the pre-enrichment broth was simultaneously inoculated into 10 mL of selenite cysteine broth and enriched at 37[degrees]C for 22 hours and 48 hours. Both enrichment broths were streaked onto xylose lysine deoxycholate agar (Merck) and Salmonella-Shigella agar, and incubated at 37[degrees]C for 22 hours.
For selective plating, presumptive Salmonella colonies from selective plates were confirmed with the API 20E identification system (BioMerieux). The Enterobacteriaceae strain was isolated with Levine-EMB agar (Merck). The plates were incubated at 37[degrees]C for 18 hours, and colonies growing on the plates were examined under a microscope for Gram stains and tested for catalase and oxydase reactions. For identification of all strains, the API 20E identification system (BioMerieux) was used.
These analyses showed high aerobic-plate, total-coliform, fecal-coliform, and enterococci counts. Coagulase-positive Staphylococcus aureus was not detected in any samples (Table 1).
The frequencies with which the bacteria were recovered from samples are given in Table 2. Citrobacter freundii and Enterobacter cloacae were recovered most frequently (from 28 percent of samples). Other Gramnegative bacteria that were frequently isolated were Escherichia coli (16 percent), Enterobacter sakazakii (12 percent), Klebsiella pneumoniae (17 percent), and Serratia liquejaciens (11 percent).
Foodborne diseases remain an important public health threat worldwide, and one of the most important food safety hazards is associated with raw vegetables. The large number of total microorganisms and fecal-contamination indicators (E. coli, coliform, and enterococci) detected in the vegetable samples we surveyed indicates a potential health hazard to consumers. Madden has discussed potential sources of microbial contamination of fresh fruit and vegetables during growth, harvest, distribution, and processing (1992).
The bacteria that the authors found on samples belonged most frequently to the Citrobacter-Enterobacter-Serratia group of Enterobacteriaceae. Although usually regarded as human pathogens, these members of Enterobacteriaceae family have also been recognized as inhabitants of soil and plants (Wright, Kominos, & Yee, 1976). Thus, vegetables may serve as a reservoir from which the bacteria named above can colonize and infect a susceptible host.
The study reported here demonstrates that a potential for disease transmission exists when wastewater is used for irrigation. Pathogens that have been transported by wastewater can survive in soil or on crops. The actual risk of disease transmission, however, is related to whether this survival time is long enough to allow transmission to a susceptible host. The crop and the field are the link between the pathogen in the wastewater and the potential for infection. The factors controlling transmission of disease are agronomic examples of such factors are the crop grown, the irrigation method used to apply wastewater, and cultural and harvesting practices.
Consumption of salad irrigated by wastewater has been found to be responsible for shigellosis in England (Frost, McEvoy, Bentley, Andersson, & Rowe, 1995). Numerous opportunities exist for attachment and penetration of pathogenic bacteria into lettuce in the field, as well as during harvesting, processing, and marketing, especially when a contaminated product is exposed to water or is damaged (Takeuchi et al., 2001). Guo and co-authors have demonstrated that soil and water are potential reservoirs from which Salmonella can contaminate tomatoes (Guo, Chen, Brackett, & Beuchat, 2002). The pathogen can survive in most soils in high numbers for at least 45 days and can infiltrate the tissues of tomatoes during contact with inoculated soil.
This mechanism may explain the discovery of Salmonella arizonae on tomatoes in the investigation reported here. The hydroponics system used in another study provided a controlled environment in which to study the possible association of Salmonellae with aerial tissues, with minimal concerns about environmental contamination or temperature fluctuation (Guo, Iersel, Chen, Brackett, & Beuchat, 2002).
That study provided evidence that Salmonellae can be transported from an inoculated nutrient solution to the hypocotyls, cotyledons, stems, and leaves of young tomato plants. In addition, the work of Guo and co-authors (2001) revealed the ability of Salmonella to survive on or in tomato fruits throughout the course of plant growth, flowering, fruit development, and fruit maturation (2001).
Another study showed that Escherichia coli O157:H7 may be present not only on outer surfaces, but also in the inner tissues and stomata of cotyledons of radish sprouts grown from seeds experimentally contaminated with the bacterium (Itoh et al., 1998). Indeed, this mechanism can be inferred from the fact that enteric pathogens were isolated from inside vegetables during our investigation.
The fact that some bacteria and not others are present can be explained by a difference in their capacity to attach to plants. For example, Salmonella enterica attaches as well as plant-associated bacteria and significantly better than E. coli to alfalfa sprouts (Barak, Whitehand, & Charkowski, 2002).
The authors' study demonstrated that the vegetables analyzed may be an important source of foodborne bacterial-illness outbreaks in humans, especially when the vegetables are consumed raw. In addition, vegetables of these types can also be a vehicle for Giardia cysts and Ascaris eggs (Amahmid, Asmama, & Bouhoum, 1999). To protect public health, the use of raw sewage in the irrigation of the vegetable culture must be prohibited.
Septic & Sewage Pathogens and Contaminants, References & Research Articles
Although most of the information presented in the Journal refers to situations within the United States, environmental health and protection know no boundaries. The Journal periodically runs International Perspectives to ensure that issues relevant to our international constituency, representing over 60 countries worldwide, are addressed. Our goal is to raise diverse issues of interest to all our readers, irrespective of origin.
K. Ibenyassine, D.E.S.A.
R. Ait Mhand, Ph.D.
Y. Karamoko, Ph.D.
B. Anajjar, Ph.D.
M.M. Ennaji, Ph.D.
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