ORIGINAL ARTICLE Degradation of cefquinome in spiked milk as a model for bioremediation of dairy farm waste milk containing cephalosporin residues R.A. Horton 1 , L.P. Randall 1 , V. Bailey-Horne 2 , K. Heinrich 2 , M. Sharman 2 , L.A. Brunton 1 , R.M. La Ragione 1,3 and J.R. Jones 4 1 Animal & Plant Health Agency (APHA), Addlestone, Surrey, KT15 3NB, UK 2 The Food and Environment Research Agency, Sand Hutton, York, YO41 1LZ, UK 3 School of Veterinary Medicine, Faculty of Health and Medical Sciences, University of Surrey, Guildford, Surrey, GU2 7XH, UK 4 Animal & Plant Health Agency (APHA), Johnstown, Carmarthen, SA31 3EZ, UK Keywords bioremediation, cefquinome, dairy calves, extended-spectrum b-lactamase, waste milk. Correspondence Robert A. Horton, Animal & Plant Health Agency (APHA), Addlestone, Surrey KT15 3NB, UK. E-mail: robert.horton@apha.gsi.gov.uk 2014/1590: received 1 August 2014, revised 7 January 2015 and accepted 14 January 2015 doi:10.1111/jam.12765 Abstract Aims: The aims of this work were to develop a model of dairy farm waste milk and to investigate methods for the bioremediation of milk containing cefquinome residues. Methods and Results: Unpasteurized milk and UHT milk that had both been spiked with cefquinome at a concentration of 2 lg ml À1 were used as a model for waste milk containing cephalosporin residues. Adjustment of the spiked UHT milk to pH 10 or treatment with conditioned medium from bacterial growth producing cefotaximase, were the most effective methods for decreasing the cefquinome concentrations within 24 h. A large-scale experiment (10 l of cefquinome-spiked unpasteurized milk) suggested that fermentation for 22 h at 37°C followed by heating at 60°C for 2h was sufficient to decrease cefquinome concentrations to below the limit of quantification (<125 lg kg À1 ) and to kill the majority of the enriched bacterial population. Conclusions: One or a combination of the bioremediation methods described may have potential as a practical treatment for dairy farm waste milk. Significance and Impact of the Study: Treatment of waste milk to decrease cephalosporin residue concentrations and also to kill bacteria prior to feeding to dairy calves could decrease the risk of selection for ESBL bacteria on dairy farms. Introduction Waste milk (or discard milk) may be defined as milk that is unfit for human consumption because it is either derived from cows that have recently calved (and there- fore contains colostrum), or is from cows that have mas- titis or cows that are either receiving drug treatment (particularly antibiotics) or have been treated and are within the withdrawal period for that drug (Brunton et al. 2012; Randall et al. 2014). The importance of adhering to the appropriate withdrawal period or discard times to prevent milk containing drug residues from entering the human food supply has been recognized for many years (Talley 1999). Feeding waste milk to calves is common practice on some dairy farms in England and Wales (Brunton et al. 2012), Sweden (Duse et al. 2013) and in the United States of America (Pereira et al. 2014) since this ameliorates to some extent the economic losses associated with unsaleable milk and there is evidence that feeding fresh waste milk to calves can improve growth performance (Chardavoyne et al. 1979). However, it has been hypothesized that the practice of feeding waste milk to calves could be a potential risk factor for the selection of antimicrobial drug resistant bacteria (Berge et al. 2005; Schmid et al. 2013). A recent study (Randall et al. 2014) detected eight different types of b-lactam antibiotics in © 2015 Crown copyright. Journal of Applied Microbiology 118, 901–910 © 2015 The Society for Applied Microbiology. This article is published with the permission of the Controller of HMSO and the Queen’s Printer for Scotland. 901 Journal of Applied Microbiology ISSN 1364-5072