Virulence and antibiotic resistance of Enterococcus faecalis clinical isolates recovered from three states of Mexico. Detection of linezolid resistance

Background and Aims: The virulence of Enterococcus faecalis is associated with three proteins involved in biofilm production: Ace, Agg, and Esp. Isolates also vary with respect to drug resistance. The present study investigated four characteristics of clinical isolates of E. faecalis recovered from three hospitals in Mexico, including biofilm production, the presence of biofilm-related genes, antibiotic susceptibility, and clonal diversity. Methods: We studied 109 clinical isolates. Biofilm formation was investigated using crystal violet and the safranin method with biofilm index correction. The presence of ace, agg, and esp genes was determined by PCR. Susceptibility to antibiotics was determined by the broth microdilution method and clonal relatedness was determined by pulsed-field gel electrophoresis (PFGE). Results: Using the crystal violet method, 4.6% (5/109) of isolates were high biofilm producers, 48% (52/109) were moderate producers, 20% (39/109) were low producers, and 11% (12/109) were nonproducers. The agg gene was present in 44% (48/109), the ace gene in 39% (43/109), and the esp gene in 33% (36/109). The esp gene was associated with biofilm production (p <0.001), whereas the ace gene correlated with tetracycline resistance (p <0.01). The biofilm index was associated with the presence of both esp plus agg in glucose medium (p= 0.006). Clinical isolates showed high resistance to tetracycline and ciprofloxacin. Also, 2% of isolates were resistant to linezolid and there was no vancomycin resistance. PFGE revealed 109 different restriction patterns. Conclusions: The presence of the esp and agg gene was associated with biofilm production, whereas the presence of the ace gene correlated with tetracycline resistance. Overall, a moderate resistance to antibiotics was detected and there was no clonal relatedness among isolates.