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Microbial level and potential health risks of Escherichia coli O157:H7, Listeria monocytogenes, and Salmonella spp. in raw vegetables

Fresh produce forms an important part of healthy diet because they are an important source of essential nutrients, vitamins, minerals, and fibre for humans. However, epidemiological data revealed that a large number of foodborne infections are attributed to consumption of fruits and vegetables. I...

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Main Author: Kuan, Chee Hao
Format: Thesis
Language:English
Published: 2017
Online Access:http://ethesis.upm.edu.my/id/eprint/12929/1/FSTM%202017%2019%20-%20T.pdf
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language English
description Fresh produce forms an important part of healthy diet because they are an important source of essential nutrients, vitamins, minerals, and fibre for humans. However, epidemiological data revealed that a large number of foodborne infections are attributed to consumption of fruits and vegetables. It is notable that Escherichia coli O157:H7, Listeria monocytogenes, and Salmonella are the predominant foodborne pathogens that consistently contribute to major foodborne disease outbreaks associated with fresh produce. With the increased consumption of fresh vegetables year round in Malaysia, challenges exist in investigating, developing, and implementing control measures to monitor the microbiological hazards in vegetables along the food chain. The objective of this study was to carry out a biosurveillance of E. coli O157:H7, L. monocytogenes, and Salmonella in raw vegetables at farm, retail, and domestic kitchen level in Malaysia. In this study, a total of 152 samples (comprised of organic and conventional vegetables) and 149 samples (comprised of vegetables and environmental samples) were collected from retail markets and vegetable farms, respectively, in Malaysia. A combination method of most probable number-multiplex polymerase chain reaction (MPN-mPCR) was used to detect and quantify pathogens of interest. Meanwhile, samples purchased at retail markets were also analysed for mesophilic aerobic bacteria, yeasts and moulds, and total coliforms using conventional microbiological methods. From our findings, Salmonella spp., S. Enteritidis, and S. Typhimurium were more frequently detected in samples from conventional farms compared to organic farms at the prevalence of 15.3%, 9.7%, and 5.6%, respectively. Meanwhile, 96.1% of the samples from organic farms were free from pathogens of interest in this study. Conversely, results from retail level showed that L. monocytogenes were obviously observed in both organic (9.09%) and conventional vegetables (2.67%) as compared to E. coli O157:H7, S. Typhimurium, and S. Enteritidis. E. coli O157:H7 were not detected in any samples from vegetable farms and retail markets and there was only one sample contaminated with Shiga toxin producing E. coli (STEC). In addition, the isolated strains obtained from vegetable samples were characterised based on their antibiotic resistance profile. The more frightening was the multidrug resistance of L. monocytogenes and S. Enteritidis strains were detected in this study. Moreover, all the S. Enteritidis isolates demonstrated resistance to at least four antibiotics. In this study, a kitchen simulation study was conducted to evaluate the efficacy of household washing practices in removing pathogens and to determine the bacterial cross-contamination rates during food preparation. Washing under the running tap water with scrubbing for 60 s was the most effective method for removing microbial populations by approximately 1.87 to 2.65 log10 CFU. Also, final rinsing and scrubbing practices were found to enhance the efficiency of washing method. A step-wise risk assessment was performed to evaluate the potential risk of acquiring foodborne listeriosis and salmonellosis posed by L. monocytogenes and S. Enteritidis, respectively, from the consumption of raw salad vegetables in Malaysia. Results showed that the risk estimate of acquiring listeriosis and salmonellosis for whole Malaysian population were 1.14 × 10-3 cases and 298.80 cases per 100,000 population, respectively. It is worth noting that the risks of getting listeriosis and salmonellosis for Malaysians were greatly reduced to 1.18 × 10-5 cases and 4.19 cases per 100,000 population, respectively, by washing vegetables under running tap water with scrubbing for 60 s. Findings in this study suggested raw vegetables can act as a potential vehicle for transmission and harbouring multidrugresistant foodborne pathogens and thus pose a health risk to consumers. Also, these results suggested that regardless of farming methods, all vegetables should be subjected to appropriate handling practices from farm to fork to ensure the quality and safety of the fresh produce. Further studies on a bigger scale biosurveillance are recommended for a better understanding of the presence of E. coli O157:H7, L. monocytogenes, and Salmonella in raw vegetables along the entire food chain.
format Thesis
author Kuan, Chee Hao
spellingShingle Kuan, Chee Hao
Microbial level and potential health risks of Escherichia coli O157:H7, Listeria monocytogenes, and Salmonella spp. in raw vegetables
author_facet Kuan, Chee Hao
author_sort Kuan, Chee Hao
title Microbial level and potential health risks of Escherichia coli O157:H7, Listeria monocytogenes, and Salmonella spp. in raw vegetables
title_short Microbial level and potential health risks of Escherichia coli O157:H7, Listeria monocytogenes, and Salmonella spp. in raw vegetables
title_full Microbial level and potential health risks of Escherichia coli O157:H7, Listeria monocytogenes, and Salmonella spp. in raw vegetables
title_fullStr Microbial level and potential health risks of Escherichia coli O157:H7, Listeria monocytogenes, and Salmonella spp. in raw vegetables
title_full_unstemmed Microbial level and potential health risks of Escherichia coli O157:H7, Listeria monocytogenes, and Salmonella spp. in raw vegetables
title_sort microbial level and potential health risks of escherichia coli o157:h7, listeria monocytogenes, and salmonella spp. in raw vegetables
publishDate 2017
url http://ethesis.upm.edu.my/id/eprint/12929/1/FSTM%202017%2019%20-%20T.pdf
_version_ 1819311383366336512
spelling oai:ethesis.upm.edu.my:12929 http://ethesis.upm.edu.my/id/eprint/12929/ Microbial level and potential health risks of Escherichia coli O157:H7, Listeria monocytogenes, and Salmonella spp. in raw vegetables Kuan, Chee Hao Fresh produce forms an important part of healthy diet because they are an important source of essential nutrients, vitamins, minerals, and fibre for humans. However, epidemiological data revealed that a large number of foodborne infections are attributed to consumption of fruits and vegetables. It is notable that Escherichia coli O157:H7, Listeria monocytogenes, and Salmonella are the predominant foodborne pathogens that consistently contribute to major foodborne disease outbreaks associated with fresh produce. With the increased consumption of fresh vegetables year round in Malaysia, challenges exist in investigating, developing, and implementing control measures to monitor the microbiological hazards in vegetables along the food chain. The objective of this study was to carry out a biosurveillance of E. coli O157:H7, L. monocytogenes, and Salmonella in raw vegetables at farm, retail, and domestic kitchen level in Malaysia. In this study, a total of 152 samples (comprised of organic and conventional vegetables) and 149 samples (comprised of vegetables and environmental samples) were collected from retail markets and vegetable farms, respectively, in Malaysia. A combination method of most probable number-multiplex polymerase chain reaction (MPN-mPCR) was used to detect and quantify pathogens of interest. Meanwhile, samples purchased at retail markets were also analysed for mesophilic aerobic bacteria, yeasts and moulds, and total coliforms using conventional microbiological methods. From our findings, Salmonella spp., S. Enteritidis, and S. Typhimurium were more frequently detected in samples from conventional farms compared to organic farms at the prevalence of 15.3%, 9.7%, and 5.6%, respectively. Meanwhile, 96.1% of the samples from organic farms were free from pathogens of interest in this study. Conversely, results from retail level showed that L. monocytogenes were obviously observed in both organic (9.09%) and conventional vegetables (2.67%) as compared to E. coli O157:H7, S. Typhimurium, and S. Enteritidis. E. coli O157:H7 were not detected in any samples from vegetable farms and retail markets and there was only one sample contaminated with Shiga toxin producing E. coli (STEC). In addition, the isolated strains obtained from vegetable samples were characterised based on their antibiotic resistance profile. The more frightening was the multidrug resistance of L. monocytogenes and S. Enteritidis strains were detected in this study. Moreover, all the S. Enteritidis isolates demonstrated resistance to at least four antibiotics. In this study, a kitchen simulation study was conducted to evaluate the efficacy of household washing practices in removing pathogens and to determine the bacterial cross-contamination rates during food preparation. Washing under the running tap water with scrubbing for 60 s was the most effective method for removing microbial populations by approximately 1.87 to 2.65 log10 CFU. Also, final rinsing and scrubbing practices were found to enhance the efficiency of washing method. A step-wise risk assessment was performed to evaluate the potential risk of acquiring foodborne listeriosis and salmonellosis posed by L. monocytogenes and S. Enteritidis, respectively, from the consumption of raw salad vegetables in Malaysia. Results showed that the risk estimate of acquiring listeriosis and salmonellosis for whole Malaysian population were 1.14 × 10-3 cases and 298.80 cases per 100,000 population, respectively. It is worth noting that the risks of getting listeriosis and salmonellosis for Malaysians were greatly reduced to 1.18 × 10-5 cases and 4.19 cases per 100,000 population, respectively, by washing vegetables under running tap water with scrubbing for 60 s. Findings in this study suggested raw vegetables can act as a potential vehicle for transmission and harbouring multidrugresistant foodborne pathogens and thus pose a health risk to consumers. Also, these results suggested that regardless of farming methods, all vegetables should be subjected to appropriate handling practices from farm to fork to ensure the quality and safety of the fresh produce. Further studies on a bigger scale biosurveillance are recommended for a better understanding of the presence of E. coli O157:H7, L. monocytogenes, and Salmonella in raw vegetables along the entire food chain. 2017-07 Thesis NonPeerReviewed application/pdf en http://ethesis.upm.edu.my/id/eprint/12929/1/FSTM%202017%2019%20-%20T.pdf Kuan, Chee Hao (2017) Microbial level and potential health risks of Escherichia coli O157:H7, Listeria monocytogenes, and Salmonella spp. in raw vegetables. PhD thesis, Universiti Putra Malaysia. (FSTM 2017 19).
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