35 Decline in AmpC beta-lactamase-producing E. coli in a Dutch teaching hospital Introduction Antibiotic resistance caused by broad-spectrum beta-lactamase production in Gramnegative bacteria is a well-known problem in clinical settings and in the community. Extended-spectrum beta-lactamases (ESBL) in Enterobacteriaceae are generally accepted as a major cause of beta-lactam resistance (David M. Livermore et al. 2007; Jan A. J. W. Kluytmans et al. 2013; Willemsen et al. 2015). Willemsen et al studied the epidemiology of ESBL rectal carriage between 2010 and 2014 in the same teaching hospital. Although the annual prevalence of ESBL was stable, a decline was seen in the proportion of certain ESBL groups, mainly CTX-M-1-1. In addition to ESBL, AmpC beta-lactamases are increasingly recognized as a growing and clinically relevant problem (Jacoby 2009; Rodríguez-Baño et al. 2012; Park et al. 2013; Vanesa Pascual et al. 2015; V Pascual et al. 2016). Most studies have focused on the dissemination of mobile genetic elements encoding these beta-lactamases (Rodríguez-Baño et al. 2012; Park et al. 2013; V Pascual et al. 2016). However, in certain species (e.g. Escherichia coli and Shigella spp.), AmpC beta-lactamase production is not only plasmid-encoded, but can also be caused by chromosomal hyperproduction due to mutations within the promoter/attenuator region (Jacoby 2009; Jørgensen et al. 2010; Alonso et al. 2016). However, little is known on the carriage of either plasmid-encoded (pAmpC) or chromosome-encoded AmpC (cAmpC) Enterobacteriales in hospitalised patients in the North-Western European region and no studies have been performed over a multiple year period. Moreover, screening methods for ESBL, such as ESBL selective media, may not always be optimal to screen for AmpC-producing Enterobacteriales. The present study describes the prevalence of rectal carriage with AmpC beta-lactamase-producing E. coli and Klebsiella spp. in patients in Dutch hospitals during a four-year period. Materials and methods Sample collection and phenotypical AmpC testing Four yearly point prevalence surveys (PPS) were performed in the Amphia Hospital from 2013 to 2016 in the months October or November. All hospitalised patients, including patients on dialysis and day-care, were screened for AmpC carriage using rectal swabs (Eswab, Copan, Italy). After vortexing, the swab was plated on Blood Agar plate (growth control, performed since 2011) and the liquid Amies eluent was inoculated in selective tryptic soy broth, containing cefotaxime (0.25 mg/L) and vancomycin (8 mg/L) (TSB3
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