Characterisation of the CRISPR-Cas systems in <i>Enterococcus faecalis</i> from commercial broiler farm environments and its association with antimicrobial resistance

1. Clustered regularly interspaced short palindromic repeats (CRISPR)-associated proteins (Cas) systems have been highlighted for their potential applications in controlling the spread of mobile genetic elements, including antimicrobial resistance (AMR) genes. This study investigated the characteristics of CRISPR-Cas systems in <i>E. faecalis</i> from commercial broiler farms and assessed the impact of these systems on AMR.2. All <i>E. faecalis</i> isolates contained CRISPR2, and CRISPR1-Cas and CRISPR3-Cas were identified in 84 (56.4%) and 144 (96.6%) isolates. A combination of CRISPR2 and CRISPR3-Cas and a combination of CRISPR1-Cas, CRISPR2 and CRISPR3-Cas were each identified in 27 (96.4%) farms.3. There were significant differences between CRISPR-Cas systems for phenotypic AMR: CRISPR1-Cas and CRISPR3-Cas. The <i>E. faecalis</i> isolates without CRISPR1-Cas showed higher resistance to most antimicrobials and had a higher prevalence of multidrug resistance (MDR) than those with CRISPR1-Cas. However, the resistance rate against most antimicrobials and the prevalence of MDR did not differ significantly depending on the presence or absence of CRISPR3-Cas.4. The <i>E. faecalis</i> isolates without CRISPR1-Cas harboured higher levels of all AMR genes, except for <i>tetL</i>, than those with CRISPR1-Cas. However, the <i>E. faecalis</i> isolates with CRISPR3-Cas showed a significant lower prevalence of <i>tetL</i> gene and a significantly higher prevalence of <i>fexA</i> and <i>poxtA</i> genes.5. In the distribution of <i>rep</i> families, the <i>rep</i>₉ family was predominant, followed by <i>rep</i>₁, <i>rep</i>₇, <i>rep</i>₂ and <i>rep</i>₈ families. Only prevalence of the <i>rep</i>₇ family was significantly higher in the <i>E. faecalis</i> isolates without CRISPR1-Cas (15.4%) than in those with CRISPR1-Cas (0%).6. This study is the first report on the characteristics of CRISPR-Cas systems in <i>E. faecalis</i> isolated from commercial broiler farm environments, and the results supported the hypothesis that the development of antimicrobial strategies requires an understanding of the distinctive capabilities between CRISPR1-Cas and CRISPR3-Cas and their underlying resistance mechanisms.