A patient admitted to an ICU is on a central venous line for the last one week. He is on ceftazidime and amikacin. After 7 days of antibiotics, he develops a spike of fever and his blood culture is positive for gram-positive cocci in chains, which are catalase negative. Following this, vancomycin was staed but the culture remained positive for the same organism even after 2 weeks of therapy. The most likely organism causing infection is

Enterococci are present in the intestine, genital tract and saliva. They are frequently isolated from cases of urinary tract infection and wound infection. Also causes endocarditis, infection of the biliary tract, septicemia and intra-abdominal abscess complicating diveiculitis and peritonitis. Strains resistant to Penicillin and other antibiotics occur frequently, So it is essential to perform antibiotic sensitivity for proper therapy. Enterococci are intrinsically resistant to cephalosporins and offer low-level resistance to aminoglycosides. In penicillin-sensitive strains, synergism occurs with combination treatment with Penicillin and aminoglycosides. If strains showed high-level resistance to aminoglycosides, this synergism does not occur. The drug of choice in such cases is vancomycin. Recently vancomycin-resistant Enterococci have begun to emerge. The phenotypes are Van A, B, C, D and E. The mechanism is an alteration of the D-alanyl-D-alanine chain in the cell wall. Reference: Textbook of Microbiology; Anathanarayan and paniker's; 10th edition; Page no: 219