163 Summary and general discussion population. Additionally, other risk factors for intestinal carriage of ESBL-producing Enterobacterales, such as recent antibiotic or antacid use, have been identified (E. A. Reuland et al. 2016; Huizinga et al. 2017). Although to a lesser extent than ESBL, the prevalence of plasmid-encoded AmpCproducing Enterobacterales in the Netherlands has been the subject of various studies. Chapter 2 offers some valuable insights into the epidemiology of this resistance mechanism, specifically focusing on the situation in the Netherlands. Most of the studies have focused on the rectal or perineal colonization of humans, both in hospital and community settings. In the general population, the prevalence of plasmid AmpCproducing E. coli ranges between 0.2% and 1.3%, which indicates a relatively low prevalence compared to ESBL-producing E. coli (Van Hoek et al. 2015; E. Ascelijn Reuland et al. 2015; van den Bunt et al. 2017). In contrast, surveys conducted in countries across Asia and Africa have reported higher prevalences (Rodríguez-Guerrero et al. 2022). For instance, Huang et al. found that up to 16.1% of healthy adult participants in Taiwan were faecal carriers of plasmid-encoded AmpC-producing E. coli and/or K. pneumoniae (Y.-S. Huang et al. 2020). Bassyouni et al. found a prevalence of 5.0% plasmid-encoded AmpC-producing E. coli in stool samples from Egyptian healthcare workers, while Chirindze et al. reported a prevalence of 5.8% in stool samples from students in Mozambique (Bassyouni, Gaber, and Wegdan 2015; Chirindze et al. 2018). It’s important to note that variations in study populations and screening methodologies significantly hinder direct comparisons between different regions. While the prevalence of AmpC-producing Enterobacterales in the Netherlands has been the subject of limited research, comparing the results over time has been challenging due to the heterogeneity of study populations. In this thesis, Chapter 3 describes a study on the prevalence of rectal carriage among hospitalized patients over a fouryear period, providing an opportunity to analyse trends more effectively. Interestingly, our study did not observe a significant change in the prevalence of plasmid-encoded AmpC-producing E. coli during the study period. However, a decrease in chromosomalencoded AmpC-producing E. coli was detected, indicating potential variations in the dynamics of different resistance mechanisms. Similarly, a study on ESBL carriage trends among hospitalized patients revealed overall stable ESBL prevalence, while specifically observing a decrease in CTX-M-1-like ESBL genes (Willemsen et al. 2015). These findings shed light on the complex dynamics of antimicrobial resistance patterns and highlight the need for further investigation into the underlying factors influencing the prevalence and persistence of different resistance mechanisms. 9
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