Assessment of Factors Contributing to Infection Severity and High Levels of Drug Resistance in Clinical Enterococcus Isolates.

Background: Various factors, including virulence determinants, biofilm formation, and antimicrobial resistance, contribute to the severity of infections caused by Enterococcus spp.

Methods: Enterococcus isolates were obtained from hospitalized patients in Yazd, Iran, and identified using microbiological and molecular tests. High-level resistance, biofilm formation, and the genes encoding virulence factors and resistance were investigated following standard methods.

Results: Enterococcus faecalis was the most prevalent species (60.7%), followed by Enterococcus faecium (30.4%). Linezolid was highly effective, with 94.6% of isolates being susceptible. However, more than 76% of isolates exhibited resistance to rifampin, erythromycin, tetracycline, and ciprofloxacin, and 94.6% were multidrug-resistant (MDR). Additionally, 39.3% of the isolates were vancomycin-resistant enterococci (VRE) with a MIC > 32 μg/mL, and the vanA gene was detected in 35.7% of the isolates. High-level resistance to gentamicin and streptomycin was seen in 60.7% and 50% of the isolates, respectively. The most prevalent aminoglycoside resistance gene was aph(3')-IIIa (62.5%) followed by ant(6')-Ia (58.9%), and aac(6')-Ie-aph(2″)-Ia (50%). The ant(3″)-Ia was found in only one isolate. Most of the isolates (87.5%) were biofilm producers, and the distribution of virulence-encoding genes was as follows: gelE (66.1%), efaA (57.1%), asa1 (51.8%), esp (25%), cylA (19.6%), and hyl (8.9%). Furthermore, the ace gene was present in 79.4% of E. faecalis isolates, while the fnm and acm genes were found in 76.5% and 23.5% of E. faecium isolates, respectively.

Conclusions: The study highlights the significant role of notable drug resistance and the widespread presence of virulence traits in the development of enterococcal infections.