Persistence of a wild type Escherichia coli and its multiple antibiotic-resistant (MAR) derivatives in the abattoir and on chilled pig carcasses Anne A. Delsol a, ⁎, Deborah E. Halfhide a , Mary C. Bagnall b , Luke P. Randall b , Virve I. Enne c , Martin J. Woodward b , John M. Roe a a Faculty of Medical and Veterinary Sciences, University of Bristol, Langford, BS40 5DU, UK b Department of Food and Environmental Safety, Veterinary Laboratories Agency, New Haw, Surrey, KT15 3NB, UK c Department of Cellular and Molecular Medicine, University of Bristol, Bristol, BS8 1TD, UK abstract article info Article history: Received 13 July 2009 Received in revised form 12 March 2010 Accepted 14 March 2010 Keywords: Multiple antibiotic resistance (MAR) E. coli Food chain Pigs Abattoir The aim of this study was to evaluate the ability of an Escherichia coli with the multiple antibiotic resistance (MAR) phenotype to withstand the stresses of slaughter compared to an isogenic progenitor strain. A wild type E. coli isolate (345-2RifC) of porcine origin was used to derive 3 isogenic MAR mutants. Escherichia coli 345-2RifC and its MAR derivatives were inoculated into separate groups of pigs. Once colonisation was established, the pigs were slaughtered and persistence of the E. coli strains in the abattoir environment and on the pig carcasses was monitored and compared. No significant difference (P N 0.05) was detected between the shedding of the different E. coli strains from the live pigs. Both the parent strain and its MAR derivatives persisted in the abattoir environment, however the parent strain was recovered from 6 of the 13 locations sampled while the MAR derivatives were recovered from 11 of 13 and the number of MAR E. coli recovered was 10-fold higher than the parent strain at half of the locations. The parent strain was not recovered from any of the 6 chilled carcasses whereas the MAR derivatives were recovered from 3 out of 5 (P b 0.001). This study demonstrates that the expression of MAR in 345-2RifC increased its ability to survive the stresses of the slaughter and chilling processes. Therefore in E. coli, MAR can give a selective advantage, compared to non-MAR strains, for persistence on chilled carcasses thereby facilitating transit of these strains through the food chain. © 2010 Elsevier B.V. All rights reserved. 1. Introduction It is generally accepted that the use of antimicrobial agents in livestock production contributes to the increased incidence of antibiotic resistance in both commensal bacteria and pathogens (Aarestrupp et al., 2008b; Hammerum and Heuer, 2009). In 2008 59% of combined species antimicrobials sold for food animal production in the UK were authorised for pigs and/or poultry and the largest percentage of single species products was sold for use in pigs (http:// www.vmd.gov.uk/General/DARC/pubs.htm). A number of studies using a pig model have demonstrated that antimicrobial treatment regimes commonly used in the industry are responsible for increasing the number of antibiotic-resistant enteric and zoonotic bacteria in pigs (Aarestrupp et al., 2008a; Delsol et al., 2003; Delsol et al., 2004a, b). These results provide strong evidence that treated pigs have the potential to enter abattoirs with a higher number of resistant bacteria than untreated pigs, thereby increasing the risk of such bacteria moving through the food chain and infecting man. Enne et al. (2008) showed that of 2480 Escherichia coli isolated from pigs at slaughter 92% were resistant to at least one antimicrobial and 62.8% were resistant to 3 or more unrelated antimicrobials from classes used in human medicine. Multi-drug resistance in bacteria is commonly attributed to mobile genetic elements such as plasmids or transposons (Gold and Moellering, 1996; Jacoby and Archer, 1991). However chromosomal multi-drug resistance systems such as the multiple antibiotic resistance (mar) locus of E. coli may also be involved (Cohen et al., 1989; George and Levy, 1983). The mar-locus of E. coli is reported to mediate reduced susceptibility (4 to 8 fold) to a number of unrelated antimicrobials primarily by up-regulating the outflow of antimicro- bials via the AcrAB-TolC efflux pump (Okusu and Nikaido, 1996) and down-regulating influx through the Outer Membrane Protein F (OmpF) (Cohen et al., 1989). The up-regulation of the soxRS regulon has also been shown to up-regulate acrAB, resulting in the MAR phenotype (Miller et al., 1994; White et al., 1997). The MAR phenotype confers low level resistance to antibiotics such as β-lactams, tetracyclines and fluoroquinolones, resistance to organic solvents such as cyclohexane (White et al., 1997) and decreased sus- ceptibility to disinfectants such as chlorhexidines, acridines and triclosan (Mc Murray et al., 1998; Moken et al., 1997; Russell, 2000, International Journal of Food Microbiology 140 (2010) 249–253 ⁎ Corresponding author. Tel.: + 44 117 928 9478; fax: + 44 117 928 9612. E-mail address: a.a.g.delsol@bris.ac.uk (A.A. Delsol). 0168-1605/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.ijfoodmicro.2010.03.023 Contents lists available at ScienceDirect International Journal of Food Microbiology journal homepage: www.elsevier.com/locate/ijfoodmicro