16 Chapter 1 Molecular confirmation tests, such as multiplex PCRs, microarrays, and whole genome sequencing (WGS), are often required to specifically identify plasmid-encoded ampC genes and differentiate them from chromosomal ampC. WGS allows for the detection of promoter/attenuator mutations in E. coli and the examination of different plasmid families. WGS facilitates cluster analysis and confirmation of outbreaks by integrating cluster analysis results with epidemiological data (Quainoo et al. 2017). In settings where molecular diagnostics may not be accessible, the implementation of a practical algorithm for distinguishing ampC genotypes in E. coli through phenotypic susceptibility testing can be valuable. Notably, utilizing cefotaxime minimal inhibitory concentrations obtained from gradient test results demonstrated a high level of accuracy in predicting the ampC genotype. The utilization of diverse screening media in prevalence studies introduces variability in the interpretation of prevalence data. While specific media for screening ESBL are available, the options for screening AmpC-producing Enterobacterales are limited. Although there are media with increased cephamycin concentrations, the effectiveness of these media has been insufficiently studied. The effectiveness of media with increased cephamycin concentrations requires further study, and standardization of screening strategies using antibiotic enrichment broth is yet to be established. What are the sources of AmpC-producing Enterobacterales? Plasmids are extrachromosomal DNA elements that can be transferred between bacteria, often carrying antibiotic resistance genes. Plasmid-based resistance poses a significant challenge to infection control, with a particular focus on Enterobacterales carrying plasmid-mediated AmpC beta-lactamases (pAmpC-E). Certain plasmid families, such as IncA/C, IncB/O/K, and IncI, are commonly associated with blaCMY-2, the prevalent AmpC resistance gene (Accogli et al. 2013; Alessandra Carattoli et al. 2018). Notably, IncI plasmids, including the prevalent IncI-ST12 sequence type, have been detected in diverse sources, including human clinical samples, traveller rectal carriage samples, livestock samples, and dog samples (Lorme et al. 2018; Hansen et al. 2016). The transmission mechanisms of these blaCMY-2-carrying IncI plasmids remain to be fully understood. The origin of the promoter/attenuator mutations that lead to ampC hyperexpression in E. coli is difficult to confirm due to the phenomenon of convergent evolution, where mutations can independently reoccur in multiple isolates and separate lineages. This process, known as homoplasy, is potentially influenced by selective pressure from the
RkJQdWJsaXNoZXIy MTk4NDMw