A patient admitted to an ICU is on 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:

Enterococcus faecalis is gram-positive cocci in chains and are catalase-negative. Enterococci resistant to multiple drugs (e.g., penicillins, aminoglycosides, and vancomycin) have emerged. Vancomycin-resistant enterococci (VRE) are impoant causes of nosocomial infections; there is no reliable antibiotic therapy for these organisms. At present, two drugs are being used to treat infections caused by VRE: linezolid and daptomycin. Ref: Levinson W. (2012). Chapter 15. Gram-Positive Cocci. In W. Levinson (Ed), Review of Medical Microbiology & Immunology, 12e.