ESBL-producing E. coli in Austrian sewage sludge Franz Ferdinand Reinthaler a, *, Gebhard Feierl a , Herbert Galler a , Doris Haas a , Eva Leitner a , Franz Mascher a , Angelika Melkes a , Josefa Posch a , Ingrid Winter b , Gernot Zarfel a , Egon Marth a a Institute of Hygiene, Microbiology and Environmental Medicine, Medical University of Graz, Universita ¨tsplatz 4, 8010 Graz, Austria b Styrian Provincial Government, Specialized Division 19D, Waste and Material Flow Management, Graz, Austria article info Article history: Received 9 October 2009 Received in revised form 24 November 2009 Accepted 27 November 2009 Available online 1 December 2009 Keywords: Sewage sludge Antibiotic resistance E. coli ESBL abstract The aim of this study was to investigate the degree of contamination of sewage sludge with ESBL-producing Escherichia coli strains and the effectiveness of different sewage sludge treatment methods. Monthly sewage sludge samples were collected between January and September 2009 in 5 different sewage treatment plants and tested for the presence of ESBL E. coli. In addition, the number of colony forming units (CFU) of E. coli and coliform bacteria before and after the different sludge treatment methods (aerobic/anaerobic digestion, lime stabilization, and thermal treatment) was investigated. Of the 72 sewage sludge samples investigated, ESBL-positive E. coli were found in 44 (61.1%) sewage sludge samples. The classification of b-lactamase groups was carried out in 15 strains resulting in the detection of 2 different groups (CTX-M and TEM) of bla genes. All 15 of them had a CTX-M gene and 4 of these strains furthermore carried a TEM gene. With regard to the CFU of E. coli and coliform bacteria, thermal treatment and lime stabilization following dehydration sufficiently reduced pathogen concentrations. The plants using merely stabilization and dehydration showed an increase of E. coli and coli- form bacteria and thus also an increase in ESBL-producing E. coli. ª 2009 Elsevier Ltd. All rights reserved. 1. Introduction The global increase of antibiotic resistance poses not only a problem for hospitals and other medical institutions. Resistant pathogens are increasingly found in the community at large. The main reason for this development is the wide- spread use of broad-spectrum antibiotics in medicine and agriculture. The surface waters of populated regions almost always contain antibiotics which exert an evolutionary pressure on the microorganisms which they encounter (Zhang et al., 2009). In addition to the impact of antibiotics, there is also a direct introduction of bacteria already resistant to antibiotics into the environment from animal husbandry via liquid and solid manure as well as from human excretions via wastewater, e.g. by low efficacy treatment of hospital wastewater (Prado et al., 2008; Yang et al., 2009). There is an increasing concern about the growing resistance of patho- genic bacteria in the environment and their ecotoxic effects (Kummerer, 2004, 2009). Numerous studies report that urban wastewater and sewage sludge partially show high rates of antibiotic-resistant bacteria. It has also been shown that in both raw sewage and in the effluent of treatment plants the proportion of antibiotic- resistant bacteria has increased in the past years (Goni-Urriza et al., 2000; Reinthaler et al., 2003; Silva et al., 2006). Since the treatment of wastewater does not sufficiently eliminate * Corresponding author. Tel.: þ43 316 380 4386; fax: þ43 316 380 9646. E-mail address: franz.reinthaler@medunigraz.at (F.F. Reinthaler). Available at www.sciencedirect.com journal homepage: www.elsevier.com/locate/watres water research 44 (2010) 1981–1985 0043-1354/$ – see front matter ª 2009 Elsevier Ltd. All rights reserved. doi:10.1016/j.watres.2009.11.052