Effects of Water Quality and Post-Harvest Handling on Microbiological Contamination of Lettuce at Urban and Peri-Urban Locations of Ouagadougou, Burkina Faso

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Résumé

Vegetable production in urban gardens of Ouagadougou contributes to food security, but
water for irrigation is often of low quality. This is particularly acute if irrigation water is taken
from wastewater polluted channels. This study aimed at (i) verifying to what degree irrigation
water quality is correlated with contamination of lettuce with Escherichia coli, total coliforms, and
Salmonella spp., and (ii) assessing effects of post-harvest handling on pathogen development during
the trade chain. We tested pathogen removal efficiency on lettuce by applying post-harvest washing.
Irrigation water of production areas in Ouagadougou (n = 10) showed a mean E. coli load of
2.1  105 CFU 100 mL􀀀1. In 60% of the cases, irrigation water did not meet the standards of the
World Health Organization (WHO) for safe irrigation water, and in 30% of the cases, irrigation
water was contaminated with Salmonella spp. Loads of total coliforms on lettuce leaves ranged
from 2.9  103 CFU g􀀀1 to 1.3  106 CFU g􀀀1, while E. coli averaged 1.1  102 CFU g􀀀1. Results on
post-harvest handling revealed that microbial loads increased along the trade chain. Overall, half of
all lettuce samples (n = 60) were tested positively for Salmonella spp. The experiment showed that
appropriate post-harvest handling could prevent the increase of total coliforms.

Mots-clés

urban agriculture; microbiological contamination; lettuce; trade chain