Impact of Irrigation Water on the Bacteriological Quality of Lettuce (Lactuca sativa) in the Market Garden Zone of Niamey, Identification of Enterobacteria

The urban community of Niamey is characterized by a prodigious development of urban and peri-urban agriculture. Lettuce (Lactuca sativa) is one of the main crops grown in these urban and peri-urban areas. The aim of this study is to assess the impact of irrigation water on the bacteriological quality of lettuce produced in the market gardening zone of the Niamey city. Three (3) market garden sites were studied (Harobanda (site 1), Gamkallé (site 2) and Gounti yéna (site 3). Eighteen (18) lettuce samples and twenty-nine (29) irrigation water samples were taken from the market garden sites and subjected to microbiological analysis using conventional methods appropriate to each indicator. Thus, five (5) indicators of contamiantion were searched, Total Mesophilic Aerobic Flora (TMAF), total coliforms (TC), faecal coliforms (FC), enterobacteria (Ent), Faecal streptococci (FS), Escherichia coli (E. coli) and Clostridium perfringens (CP). The results showed that irrigation water samples from site 1 were highly contaminated with Total Coliforms (TC) and Faecal Coliforms (FC) (3.65±7.88.106 and 1.41±3.04. 106 CFU/100ml respectively), those from site 2 by Faecal Streptococci (FS) (1.19±2.03.105 CFU/100ml) and from site 3 by Enterobacteria (Ent) (1.61±2.37.108 CFU/100ml) and Escherichia coli (8.22±11.86.105 CFU/100ml). Thus, lettuce samples from site 1 are more contaminated with TC (5.32±8.32.106 CFU/g) and Ent (3.10±0.95.107 CFU/g). Faecal coliforms (1.35±1.13.106 CFU/g) and faecal streptococci (5.30±8.21.105 CFU/g) predominate on the site2 and finally site3 is more contaminated with E. coli (2.43±0.38.105 CFU/g). However, enterobacteria species such as Citrobacter freundii, Enterobacter cloacae, Enterobacter sakazakii, Escherichia coli1, Klebsiella pneumoniae ssp ozaenae, Pantoea spp 1, Proteus mirabilis, Raoultella terrigena, Salmonella enterica arizonae, Salmonella spp, Serratia liquefaciens, Serratia marcescens and Serratia odorifera1 were identified in irrigation water samples and lettuce at these sites. In fact, the quality of the irrigation water is not suitable for irrigation, and strongly influences the contamination of the lettuce produced by the bacteria. Consumption of this lettuce without the minimum of precautions could prove dangerous to consumers.