Physicochemical, Molecular and Cultural Identification of Microbial Pathogens in Wastewater Irrigated Crops

Abstract

Water scarcity is a global issue and the application of untreated wastewater for irrigation is a general practice in developing countries. Major drawbacks of wastewater irrigation include the presence of heavy metals and disease-causing bacterial pathogens. The present study was conducted for identification of the bacterial strains in wastewater and wastewater irrigated vegetable and crops. XLT-4 cultural media was used for culture-based detection of different bacterial pathogens (red with black center for Salmonella, yellowish for E. coli and small pink colonies for Shigella). The presence of these disease-causing pathogens was indicated in almost all samples. For further confirmation, microscopic analysis was performed, which showed gram negative rod shaped colonies. Various biochemical identification tests (catalase, urease, oxidase and lactase) also confirmed the presence of pathogenic bacterial species in analyzed samples. PCR based diagnosis was carried out using species specific primers for Mdh gene of E. coli, IpaB gene of Salmonella and IpaH gene of Shigella. 16s rRNA was amplified in all observed samples as positive control. The Mdh gene amplification was observed in wastewater, pumpkin, sugarcane, maize, brinjal, lettuce, spinach, cabbage and radish samples, while IpaB gene was amplified in pumpkin, sugarcane, maize, brinjal, lettuce, spinach, cabbage and radish samples, and IpaH gene was amplified only in lettuce. These observations depicted that wastewater irrigated vegetables and crops were highly contaminated with pathogenic bacterial strains. Therefore, treated wastewater should be used for irrigation otherwise it may lead to health problems in humans.