Scientific Research and Essays

  • Abbreviation: Sci. Res. Essays
  • Language: English
  • ISSN: 1992-2248
  • DOI: 10.5897/SRE
  • Start Year: 2006
  • Published Articles: 2763

Full Length Research Paper

Bacterial contamination of lettuce and associated risk factors at production sites, markets and street food restaurants in urban and peri-urban Kumasi, Ghana

F. Amponsah-Doku1, K. Obiri-Danso1*, R. C. Abaidoo1, L. A. Andoh1, P. Drechsel2 and F. Kondrasen3
1Department of Theoretical and Applied Biology, Kwame Nkrumah University of Science and Technology, Kumasi, Ghana. 2International Water Management Institute, Accra, Ghana. 3 University of Copenhagen, Denmark.
Email: [email protected]

  •  Accepted: 09 October 2009
  •  Published: 31 January 2010


There is increasing evidence that urban grown vegetables in developing countries can be contaminated with pathogenic microorganisms. This is particularly true when wastewater is used in irrigation. The microbiological quality of wastewater grown lettuce on farms, markets and at street food vendor sites were evaluated for thermotolerant coliforms, enterococci and Salmonella using standard methods. Farm irrigation water and market refreshing water (water used in keeping the lettuce fresh) samples were also analysed. Thermotolerant coliforms on lettuce varied from 2.3 × 103 to 9.3 × 108 on farm, 6.0 × 10to 2.3 × 10on market and 2.3 x 106 to 2.4 x 109 at street food vendor sites. Indicator bacterial numbers on farm lettuce were higher compared to the irrigation water (1.5 × 103 to 4.3 × 106) used on the farms. Thermotolerant coliform numbers in market refreshing water(9.0 × 103 to 4.3 × 1010) were higher compared to that on the market lettuce.Enterococci numbers on lettuce were lower and ranged from 3.9 × 101 to 1.0 × 106 on farm, 6.0 × 101 to 9.0 × 104 on market and 5.1 x 10to 2.5 x 106 at street food vendor sites. Salmonella numbers recorded at food vendor sites ranged from 1.5 × 101 to 9.3 × 102. In general, thermotolerant coliforms numbers increased by 18% while enterococci numbers reduced by 64% from the farms to the street foods. Bacterial counts on farm lettuce and irrigation water, market lettuce and refreshing water and street foods all exceeded the recommended World Health Organization (WHO) and International Commission on Microbiological Specifications for Food (ICMSF) standards of 103. Wastewater use on farms and refreshing water in markets could be the main contributors to lettuce contamination and that education on use of effective de-contamination or washing methods before eating will contribute to reducing the risk associated with the consumption of such contaminated foods.


Key words: Salmonella, irrigation water, thermotolerant coliforms, enterococci, lettuce.