Performance of Isfahan North Wastewater Treatment Plant in the Removal of Listeria monocytogenes

Listeria and in particular Listeria monocytogenes is considered a ubiquitous foodborne pathogen which can lead listeriosis in human and animals. Listeriosis can be serious and may cause meningitis، septicemia and abortion in pregnant women. Although wastewater or sludge may contaminate foods of plant origin، there are no data on occurrence of Listeria spp. in wastewater and sludge in Iran. The purpose of current investigation was to study the occurrence of Listeria spp. in various samples of wastewater and sludge in Isfahan North wastewater treatment plant. Influent، effluent، raw sludge and dried sludge samples were collected from Isfahan North municipal wastewater treatment plant. L. monocytogenes were enumerated by a three–tube most probable number (MPN) assay using enrichment Fraser broth. A total of 65 various samples from five step in 13 visits were collected. The presence of Listeria spp. also was determined using USDA procedure. Then، phenotypically identified L. monocytogenes were further confirmed by Polymerase Chain Reaction amplification. L. monocytogenes isolated from 76. 9%، 38. 5%، 84. 6%، 69. 2% and 46. 2% of influent، effluent، raw sludge، stabilized sludge and dried sludge respectively. The efficiency of wastewater treatment processes، digester tank and drying bed in removal L. monocytogenes were 69. 6%، 64. 7% and 73. 4% respectively. All phenotypically identified L. monocytogenes were further confirmed by Polymerase Chain Reaction. The results of present study have shown that Listeriaspp. and L. monocytogenes in particular، were present in wastewater treatment plant effluents and sludge at high level. The bacteria may spread on agriculture land and contaminate foods of plant origin. This may cause a risk of spreading disease to human and animals.