LISTERIA SPECIES INCIDENCE AND CHARACTERIZATION IN A RIVER RECEIVING TOWN SEWAGE FROM A SEWAGE-TREATMENT PLANT

This study evaluated the ability of a sewage treatment plant to elimin ate Listeria species and the incidence of Listeria species in the rive r receiving the effluent. The average efficiency of removal of Listeri a species in the treatment plant was 92%. Despite the efficiency of th e plant being within the limits established by the EC Directive in ter ms of BOD5 decrease, an increase in the levels of Lislen'a species was still observed downstream from the plant. The species isolated with g reatest frequency, both in the influent and effluent as well as the ri ver water, was L. monocytogenes followed by L. seeligeri and L. welshi meri. L. ivanovii was only found in very low proportions in the river samples. The analysis of the sensitivity of Listeria species to 22 ant imicrobial agents demonstrated the presence of a high percentage of ba cteria resistant to aztrenam, cefuroxme, cetriaxone and to a leser deg ree moxalactam and cefotaxime. in contrast, resistance to aminoglycosi des and tetracycline was only observed in a low number of isolates. (C ) 1997 IAWQ. Published by Elsevier Science Ltd.