Listeria monocytogenes was isolated from a sewage treatment plant in Baghdad, Iraq, at all stages of treatment. The treatment processes did not yield a sewage sludge cake or a final discharge free of listerias. The agricultural practice of using such sewage products as fertilizers could become a route of spreading the organism in Iraq, particularly by infecting animals that consume vegetation in fields spread with such sewage. Dewatering of sewage reduced the number of L. monocytogenes but long periods of exposure to sun would be needed to obtain a 'safe' sewage sludge cake.

Listeria monocytogenes was found in the sewage sludge cake which is commonly used as an agricultural fertilizer in Iraq. Soils treated with this material were contaminated with the organism. Pot and field experiment showed that crops grown on treated soil became contaminated with L. monocytogenes and when alfalfa plant was grown on farmland soil treated with sewage sludge cake, listerias were found on 10% of 50 plants sampled at harvest, but the organism was detected only in low numbers on these crops (less than or equal to 5 cells/g). This could add to the risk to animals and man.

No abstract

Two sewage treatment plants in Baghdad, Iraq, were investigated to assess the effects of the different treatment stages on the removal of Listeria monocytogenes. The bacteria were severely affected after the activation and digestion stages at both plants. A dramatic decrease in numbers of listerias after each of these two stages was noticed during the cold months (September-January). The organisms were able to survive these treatments and were present in the final effluent and even in low numbers in the sewage sludge cake. Sufficient dewatering of sewage sludge is recommended to obtain sewage free of listerias. Improvements in the isolation procedure of L. monocytogenes from such heavily contaminated material is also discussed.

No abstract