Skip to main content

Systematic review on the microbiological quality of fresh vegetables and ready-to-eat salad in Nigeria



The consumption of fresh vegetables and salads has become popular, and because of a greater understanding of health benefits, these are most often eaten raw or with minimal processing.

Main body of the abstract

The microbiological safety of these vegetables is necessary and the possible source of contamination includes microbial contamination of raw produce, workers hygiene and the condition of the environment and equipment used to process the salad and fresh vegetable for distribution. This article reviewed the previously published literature on the microbiological quality of fresh vegetable and salad. There was 100% isolation of bacteria in all of the studies review which include Escherichia coli, Aspergillus spp., Staphyloccocus aureus, Salmonella, Klebsiella spp., Actinomycetes, Bacillus subtilis, Pseudomonas aeroginosa, Staphyloccocus epidermidis, Bacillus spp., Shigella spp., Lactobacillus and Streptoccocus spp.

Short conclusion

The review study recommended that fresh vegetables and salad should be properly washed with clean water before preparing.


World Health Organization (WHO) estimated more than 500 children died daily from the consumption of contaminated food and water (WHO 2015). It was reported that illnesses due to contaminated foods are an important cause of reduced economic productivity (Okonko et al. 2008). The incidence rate of foodborne diseases is also rising in, both developed and developing nations due to problems compounded by poverty, inadequate sanitary conditions and poor general hygiene (Udo et al. 2009).

Foodborne illnesses are associated with significant morbidity and mortality rates worldwide (Scallan et al. 2011). Globally, an estimated 2 million people died from diarrheal diseases in 2011 and approximately 70% of these are foodborne. It is estimated 30% of the population in Nigeria are affected by foodborne disease annually (WHO 2011).

Also in Africa, it was estimated that 92 million people fall ill from consuming contaminated foods, resulting in 137,000 deaths each year (Narayan et al. 2017). Foodborne illnesses are major threat to health of people in Nigeria. In 1997, Local Government Health Systems profile for Nigeria reported leading causes of deaths in different geo-political zones to foodborne associated illnesses, which accounted for 25% of mortality followed by malaria (21%) and accidents (19%), while the Federal Ministry of Health in 2007, 90,000 cases of food poisoning was reported (FAO/WHO 2008).

Although the full extent of the burden and cost of unsafe food is unknown, the impact on global health and development are considered to be immense. The incidences of foodborne pathogens have been studied in Nigeria with more than 90% of annual cases of food poisoning reported to be caused by Escherichia coli, Salmonella spp., Shigella spp., Proteus spp., Bacillus cereus, (Enabulele et al. 2010; Eni et al. 2010; Onyeneho and Hedberg 2013; Adekanle et al. 2015; Ajayi et al. 2017; Negbenebor et al. 2019).

Fresh vegetables served as essential components of healthy diet whose, consumption rates increased in recent years (Sararaj et al. 2014). However, fresh vegetables are also associated with some risks to consumers (Soltan et al. 2015). Greater awareness and desire for healthier life style have led to increase consumption of fresh vegetable and fruits. Vegetables are recognized as an important source of micronutrients, carbohydrates, antioxidants, minerals, vitamins and fibers (Sararaj et al. 2014). Major human pathogens are recognized to be transmitted via uncooked vegetables (Gu et al. 2011).

The production process, use of poor quality in irrigation of farm plots, use of animal manure to fertilize soil and poor labourer hygiene have contributed to spreading of contaminants (Golly et al. 2016).

A number of studies have reported the isolation of pathogenic organisms from fresh vegetables from different points of the world as, enteric pathogens from wide variety of produce including Listeria monocytogenes, Salmonella spp, and Escherichia coli (E. coli), Staphylococcus aureus (S. aureus), Clostridium perfringes, Campylobacter jejuni and Campylobacter coli were reported in different regions of the world (Bukar et al. 2010; Eni et al. 2010; Denis et al. 2016; Golly et al. 2016).

The aim of this study is to review published articles on the microbiological quality of fresh vegetables and salad.


Literature search

Articles published between January 2000 and September 2019 were retrieved from Medline via Pubmed, Biomed, Ajol and google scholar database using the following search terms; “fresh vegetables, microbial quality, salad and vegetables”. The review was performed using the preferred reporting items for systematic review and Meta-analysis (PRISMA) statement.

Articles selection and data extraction

The titles and abstracts of all potential papers were assessed to ensure all studies had been identified and duplicates removed. Relevant data were extracted using a database that listed the variables; author, year of study, location of study, methods of identification, commonest microorganism isolated, vegetables fresh produce components, quantitative indicators of fresh vegetables contamination, and microbial count were summarized.

Data synthesis

Using the PRISMA statement, data were extracted and reported as outlined by authors without any alteration following the search, a total of 325 articles were identified, duplicates were removed and 309 records excluded because the microbial quantity was not determined as well as incompatible title and abstract. One article was excluded due to inability to access the journal and irrelevant outcome compared to the objectives. Altogether, fifteen articles were included in the final data synthesis.

Main text

figure a

In seven previous studies, percentage of vegetable tested produced high bacterial load (Aboh et al. 2011; Eni et al. 2010; Adeshina et al. 2012; Owolabi 2013; Adekanle et al. 2015; Oji 2016; Negbenebor et al. 2019). Five studies indicated high bacterial load of contaminated vegetables without percentage of the microorganism (Uzeh et al. 2009; Abdullahi and Abdulkareem 2010; Oluwafemi et al. 2013; Nwankwo et al. 2015; Oji 2016). Only four studies analyzed in this review were able to isolate fungi (Uzeh et al. 2009; Oluwafemi et al. 2013; Adekanle et al. 2015; Nwankwo et al. 2015).

There was 100% isolation of bacteria in all of the studies analyzed which include Escherichia coli, Staphyloccocus aureus, Salmonella, Klebsiella spp., Bacillus subtilis, Actinomycetes, Pseudomonas aeroginosa, Staphyloccocus epidermidis, Bacillus spp., Shigella spp., Lactobacillus and Streptoccocus spp. Base on isolates obtained at individual fresh vegetables, cabbage (88.3%), cucumber (46.66%) and carrot (66.66%) from studies nine (Table 1).

Table 1 Microbiological quality of fresh vegetables and salad


Microorganisms found in salad and fresh vegetables explain the sanitary and hygienic quality of cultivation water, harvesting, transportation, storage and processing of products. All bacteria isolates reported in this review study have been previously isolated from salad vegetables and fresh vegetables in other studies basically in Nigeria. Various researches had different result methods documented; some quantify the bacterial load count in salad vegetables and fresh vegetables, while others quantify the microorganism isolated in percentage. Five studies of Uzeh et al. (2009), Abdullahi and Abdulkareem (2010), Eni et al. (2010), Oluwafemi et al. (2013) and Nwankwo et al. (2015) determined the bacterial load in each of these salads and fresh vegetables, i.e. lettuce, cabbage, cucumber and carrot. They only isolated the organism but did not determine the percentage. But Eni et al. (2010), Afolabi et al. (2011), Aboh et al. (2011), Adeshina et al. (2012), Osamwonyi et al. (2013), Wogu and Iwezeuna (2013), Owolabi (2013), Adekanle et al. (2015) and Negbenebor et al. (2019) determined the range of bacterial load and the percentage occurrence of the isolated microorganism which serves as an advantage over other studies.

The isolation of these organisms in the various studies is very disturbing as these samples were reported to be obtained from big fast food centre; most samples were supposedly ready to eat and others from the market. The high incidence of bacterial contamination of the ready to eat salad and fresh vegetables may be due to unhygienic practices. Restaurant staff may not observe basic sanitation requirement for processing products that required no pre-heating before consumption. Another reason may be the non-availability of water in good quantity and quality for washing of fresh vegetables and mass production of salad in big fast food centres. Based on Uzeh et al. (2009) and Oluwafemi et al. (2013), carrot was the more contaminated vegetable, followed by lettuce and cabbage was also high in three various studies (Abdullahi and Abdulkareem 2010; Eni et al. 2010; Nwankwo et al. 2015).


From the results obtained from the reviewed studies of the microbiological quality of fresh vegetables and ready-to-eat salad, it can be inferred that fresh vegetables and ready-to-eat salad may be contaminated with pathogenic or non-pathogenic microorganisms. Therefore, fresh vegetables and salad should be properly washed with clean water before preparing, maintenance of personnel and kitchen hygiene, during preparation of salad, fresh vegetables other food substance for meal.

Availability of data and materials

Not applicable in this section.


  • Abdullahi IO, Abdulkareem S (2010) Bcaterial uality of some ready-to-eat vegetable as retailed and consumed in Sabo-Gari, Zaria, Nigeria. Bayero J Pure Appl Sci 3(1):173–175

    Google Scholar 

  • Aboh MI, Oladosu P, Ibrahim K (2011) Bacterial contamination of salad vegetables in Abuja municipal area Council, Nigeria. Malays J Microb 7(2):111–114

    Google Scholar 

  • Adekanle MA, Effedua HI, Oritogun KS, Adesiji YO, Ogunledum A (2015) A study of microbial analysis offresh fruit and vegetablein sagamu markets South-West, Nigeria. Agroserach 15:21–22

    Google Scholar 

  • Adeshina GO, Samuel DJ, Victor EG (2012) Antibacterial susceptibility pattern of pathogenic bacteria isolates from vegetables salad sold in restaurant in Zaria. J Microb Res 2(2):5–11

    Article  Google Scholar 

  • Afolabi OR, Oloyede AR, Ibrahim TA (2011) Evaluation of pathogenic bacteria associated with fresh produce obtained from selected market in Abeokuta. J Sci Sustain Dev 4:75–81

    Article  Google Scholar 

  • Ajayi OA, Amokeodo MI, Akinwunmi OO (2017) Microbial quality of selected ready-to eat vegetables from Iwo, Nigeria and effectiveness of rinsing agent. Appl Trop Agric 22(2):131–137

    Google Scholar 

  • Bukar A, Uba A, Oyeyi TI (2010) Occurrence of some enteropathogenic bacteria in some minimally and fully processed ready-to-eat foods in kano metropolis, Nigeria. Afr J Food Sci 4(2):032–036

    Google Scholar 

  • Denis N, Zhang H, Leroux A, Trudel R, Bietlot H (2016) Prevalence and trends of bacterial contamination in fresh fruits and vegetables sold at retail in Canada. Food Control 67:225–234

    Article  Google Scholar 

  • Enabulele SA, Amune PO, Aborisade TA (2010) Antibiograms of Salmonella isolates from poultry farms in Ovia North East Local Government Area, Edo State, Nigeria. Agric Biol J N Am 1:1287–1290

    Article  Google Scholar 

  • Eni OA, Oluwawemitan IA, Solomon OU (2010) African microbial quality of fruits and vegetables sold in Sango Ota, Nigeria. J Food Sci 4(5):291–296

    Google Scholar 

  • Food and Agriculture Organization and World Health Organization (2008) The Nigerian experience on food safety regulations. In: FAO/WHO global forum of food safety regulations

  • Golly MK, Salifu PS, Mills-Robertson FC (2016) Resistance of bacteria isolates from cabbage (Brassica oleracea), carrots (Daucus carota) and lettuce (Lactuca sativa) in the Kumasi Metropolis of Ghana. Int J Nutr Food Sci 5:297–303

    Article  CAS  Google Scholar 

  • Gu G, Jiahuai HU, Juau MC, Susanna MR, Jerry A (2011) International colonization of Salmonella enterica serovar typhimurium tomatoes plant. PLoS ONE 6(11):e27340

    Article  ADS  CAS  Google Scholar 

  • Narayan P, Victor BA, Djidjoh JH, Maitshwarelo M (2017) Prevalence of foodborne pathogens in food from selected African countries—a meta-analysis. Int J Food Microb 249:35–43

    Article  Google Scholar 

  • Negbenebor HE, Marami FM, Nura S (2019) Prevalence of bacterial load on some fruit and vegetables solg in Kaduna central Market, North-weastern Nigeria. J Appl Sci 19(1):20–24

    Google Scholar 

  • Nwankwo IU, Eze VC, Onwuakor CE, Friday JU (2015) Evaluation of the degree of contamination of salad vegetable sold in Umuahia main market. Am J Microb Res 3:41–44

    Google Scholar 

  • Oji PC (2016) Bacteriological analysis of salad vegetable in Eke Awka Mraket Anambra State, Nigeria. Int J Sci Res Publ 6:305–312

    Google Scholar 

  • Oluwafemi F, Akisanya E, Odeniyi K, Salami W, Sharomi T (2013) Microbiologica quality of stree-vened food and ready-to-eat Vegetables in some Nigeria Cities, Africa. J Biomed Res 16:163–166

    Google Scholar 

  • Okonko IO, Ogunjobi AA, Fajobi EA, Onoja BA, Babalola ET, Adedeji AO (2008) Comparative studies and microbial risk assessment of different ready-to-eat (RTE) frozen sea-foods processed in Ijora-Olopa, Lagos State, Nigeria. Afr J Biotechnol 7(16):2898–2901

    Google Scholar 

  • Onyeneho SN, Hedberg CW (2013) An assessment of food safety needs of restaurants in Owerri, Imo State, Nigeria. Int J Environ Res Public Health 10:3296–3309

    Article  Google Scholar 

  • Osamwonyi OU, Obayagbona ON, Aborishade W, Folisaka. (2013) Bacteriological quality of vegetable salads sold at restaurant within Okada Town, Edo State, Nigeria. Afr J Basic Appl Sci 5(1):37–41

    Google Scholar 

  • Owolabi OJ (2013) Active ileum relaxant fraction from the leaves of Ficus capensis Thunb (Moraceae), Nigeria. J Pharm Sci 12(1):1–7

    MathSciNet  Google Scholar 

  • Sararaj P, Stella D, Reetha D (2014) Microbial spoilage of vegetable and its control measures. Int J Nat Prod Sci 2(2):1–12

    Google Scholar 

  • Scallan E, Hoekstra RM, Angulo FJ, Tauxe RV, Widdowson MA, Roy SL (2011) Foodborne illness acquired in the United States—major pathogens. Emerg Infect Dis 17:7–15

    Article  Google Scholar 

  • Soltan MM, Dalla M, Shojaei MK, Sharifi Y, Vahedi S (2015) Microbial contamination of fresh vegetables and salad samples consumed in Tehran, Iran. J Food Qual Hazard Control 2:139–143

    Google Scholar 

  • Udo S, Andy I, Umo A, Ekpo M (2009) Potential Human pathogen (Bacteria) and their antibiogram in ready to eat salad sold in Calabar, South-South, Nigeria. Internet J Trop Med 5(2):1

    Google Scholar 

  • Uzeh RE, Alade FA, Bankole M (2009) THE Microbial quality of Pre-packed mixed vegetables salad in some retail outlets in Lagos, Nigeria. Afr J Food Sci 3(9):270–272

    CAS  Google Scholar 

  • Wogu MD, Iwezeuna I (2013) Microbial quality of ready to eat salad sold Benni City, Souther Nigeria. Int J Sci Technol 2(2):26–38

    Google Scholar 

  • World Health Organization [WHO] (2011) Initiative to estimate the Global Burden of Foodborne Diseases: Information and publications. Retrieved June 26, from (2011).

  • World Health Organization (WHO) (2015) Foodborne disease Fact sheet N°330".

Download references


We wish to express our profound gratitude to the management of Ahmadu Bello University, Zaria for their unreserved support toward this research work and as well as the Ahmadu Bello University Pharmaceutical Microbiology staff for their support rendered.


Not applicable in this section.

Author information

Authors and Affiliations



This review article intends to discuss on the potential risk of contamination of vegetables. IP—wrote the second and final draft, SY—wrote the first draft, GO—review manuscript, AB—review manuscript and BO—conceive the Idea and review the manuscript. All the authors’ general statement was good. All authors have read and approved the manuscript.

Corresponding author

Correspondence to Igba Profit.

Ethics declarations

Ethics approval and consent to participate

Ethical clearance was obtained from Ahmadu Bello University Zaria, Kaduna State. (ABUCUHSR/2019/002). Name of ethical committee in Ahmadu Bello University Zaria, Nigeria. 1. Prof. I.H. Nock- Chairman of ABUCUHSR. 2. Dr. M.K. Lawan- Member of Committee. 3. Prof. G.O. Adeshina- Chairman of supervisor team and committee member.

Consent for publication

Not applicable in this section.

Competing interests

The authors have no competing interest.

Additional information

Publisher's Note

Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.

Rights and permissions

Open Access This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if changes were made. The images or other third party material in this article are included in the article's Creative Commons licence, unless indicated otherwise in a credit line to the material. If material is not included in the article's Creative Commons licence and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this licence, visit

Reprints and permissions

About this article

Check for updates. Verify currency and authenticity via CrossMark

Cite this article

Profit, I., Yunus, A.S., Adeshina, G.O. et al. Systematic review on the microbiological quality of fresh vegetables and ready-to-eat salad in Nigeria. Bull Natl Res Cent 45, 185 (2021).

Download citation

  • Received:

  • Accepted:

  • Published:

  • DOI: