44 Chapter 3 swabs to study the new screening agar. Loss of sensitivity because of the addition of cefoxitin was expected to be negligible, as most AmpC producing isolates described in literature have increased MIC’s for cefoxitin (Jacoby 2009; Tracz et al. 2007; Philippon, Arlet, and Jacoby 2002). The switch in media is unlikely to be the reason for the decline in AmpC. Using both cefotaxime and ceftazidime might even increase the sensitivity, using two different cephalosporin antibiotics. Only the blaACC-like producing isolates could be of concern, which are known to have lower MIC’s for cefoxitin (Philippon, Arlet, and Jacoby 2002). However, we did not find any blaACC-like producing isolates with either of the used agars. Still, a comparative study on the diagnostic performance of screening agars for AmpC producing isolates, might provide more insight into this matter. Another limitation of our study is the use of a micro-array system. Although we assume that the AmpC phenotype can be related to the microarray- and Sanger sequencing data, we cannot discard that micro-array system only recognize the six main plasmid AmpC-like groups (blaCMY-2-like, blaDHA-like, blaACC-like, blaACT/MIR-like, blaFOXlike, blaCMY-1/MOX-like). Although former studies showed robust sensitivity and specificity of the microarray check MDR CT103, it is limited to these specific targets (Cuzon et al. 2012; Cunningham SA ; Vasoo S ; Patel R 2016; Pierre Bogaerts et al. 2016). We did not perform reverse-transcriptase PCR, as described by Trazc et al. (Tracz et al. 2007). Nevertheless, we expect that hyperproduction of AmpC is likely when known alterations in promoter and attenuator region were found as described in this paper. It is difficult to ascertain the cause of the decrease in cAmpC during the four-year period. The link between trends in e.g. ESBL and pAmpC and the dissemination of these beta-lactamases in the environment (e.g. food products, livestock, companion animals), as well as the influence of antibiotic usage in both humans and livestock, is under debate. Carriage of cAmpC has been described in studies on veal calves, broilers and companion animals within the Netherlands (Hordijk, Wagenaar, van de Giessen, et al. 2013; Huijbers et al. 2014; C. M. Dierikx et al. 2012; Hordijk, Schoormans, et al. 2013). The study by Hordijk et al. showed an increase of cAmpC in veal cattle in the period 1997 to 2010 (Hordijk, Wagenaar, van de Giessen, et al. 2013). Between 2009 to 2015 a decrease of 58.4% of antibiotic sales in the livestock sector was achieved (Veldman, K.T. , Mevius, D. J. 2016). However, to our knowledge, no new data on cAmpC prevalence in livestock in the Netherlands has been published since the decrease in antibiotic sales. Therefore, we can only speculate on the possible impact of the antibiotic decrease in the veterinary sector and the decreasing trend we found.
RkJQdWJsaXNoZXIy MTk4NDMw