Molecular Profiling of CRISPR-Cas System, Virulence Traits, and Antimicrobial Resistance in Enterococcus faecalis...

Enterococcus faecalis is responsible for life-threatening enterococcal infections. This study is aimed at investigating virulence factors, antimicrobial resistance patterns, and molecular characteristics of clinical E. faecalis isolates.

A total of 42 E. faecalis isolates were collected. Antimicrobial resistance and the minimum inhibitory concentrations (MICs) of vancomycin and gentamicin were determined using standard microbroth dilution method. The presence of virulence, antibiotic resistance, and CRISPR-Cas genes was investigated by polymerase chain reaction (PCR). Biofilm formation was also assessed, and the genetic diversity of the isolates was analyzed using enterobacterial repetitive intergenic consensus-polymerase chain reaction (ERIC-PCR).

The highest resistance rates were observed for gentamicin and ampicillin, and all isolates were high-level gentamicin resistant (HLGR) (MICs ≥ 500 μg/mL). Vancomycin resistance was detected in 15 isolates (35.7%) (MICs ≥ 32 μg/mL). Thirty-nine isolates (92.8%) were biofilm producers. The efaA gene was the most frequently detected (95.2%), followed by esp (69%), gelE (66.6%), ace (66.6%), and asa1 (57.1%). The aac(6  ^')-Ie-aph(2  ^″)-Ia gene was detected in all isolates (100%), followed by ermB (78.6%), ermA (38.1%), ermC (23.8%), and vanA (19%). CRISPR3 was the most frequently detected locus (80.95%), followed by CRISPR1 (50%), CRISPR1-cas csn1 (23.8%), and CRISPR2 (9.5%). The CRISPR3-cas csn1 gene was not detected in any isolate. High heterogeneity was observed among the isolates, with 35 different ERIC types identified.

This study demonstrated notable resistance traits and high genetic diversity among clinical E. faecalis isolates, but no statistically significant association was found between CRISPR-Cas genes and phenotypic or genotypic resistance.