Group D streptococci. Enterococci: Antibiotic Resistance.

Question 1

Group D Streptococci

Answer 1

Group D includes Enterococcus species and non-enterococcal group D streptococci, both catalase-negative, gram-positive cocci. Non-enterococcal group D streptococci include S. bovis and S. equinus. These organisms are part of the normal flora of the gastrointestinal tract. Group D streptococci can cause infections such as endocarditis, urinary tract infections, and bacteremia, often in patients with underlying conditions like colon cancer or prosthetic devices. They are identified by Lancefield grouping, bile-esculin test positive, and growth in 6.5% NaCl (for enterococci). Treatment usually involves penicillin or vancomycin for resistant strains.

Question 2

Enterococci

Answer 2

Enterococci, especially Enterococcus faecalis and Enterococcus faecium, are normal gut flora but can cause serious infections like endocarditis, urinary tract infections, and intra-abdominal infections. They are identified by their ability to grow in 6.5% NaCl and bile-esculin agar, distinguishing them from other streptococci. They are often resistant to many antibiotics, including cephalosporins and aminoglycosides. Vancomycin-resistant enterococci (VRE) have become a significant hospital-associated pathogen, spreading through plasmid-mediated transfer of resistance genes. Treatment involves linezolid, daptomycin, or tigecycline for VRE.

Question 3

Enterococcal antibiotic resistance

Answer 3

Enterococci are inherently resistant to many antibiotics, including beta-lactams and clindamycin. They possess intrinsic resistance to cephalosporins and can acquire resistance to vancomycin (VRE). The vanA and vanB genes confer vancomycin resistance, with vanA providing high-level resistance to vancomycin and teicoplanin. VRE is primarily acquired in healthcare settings, spreading through patient-to-patient contact, contaminated surfaces, or medical devices. Resistance to aminoglycosides is common, but synergy with beta-lactams may sometimes be used for treatment. Infections with VRE often require combination therapy or use of alternative agents like linezolid or daptomycin.