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-
Ans. is 'c' i.e., Enterococcus fecalis Option 'a' & 'cl' can be excluded by following information in question : ? 1) The isolated cocci are arranged in chains while staphylococci are arranged in grape like clusters. 2) The isolated organism is catalase negative while staphylococci are catalase positive. Now two options are left :? Option 'b' - Viridans streptococci Option 'c' - Enterococcus fecalis These two can be differentiated by following points :- 1)Enterococci are a frequant cause of nosocomial bacteremia in patients with intravascular catheters, while viridans streptococcal bacteremia occurs in neutropenic patients, paicularly after bone marrow transplantation or high dose chemotherapy for cancer. 2)Enterococci are intrinsically resistant to all cephalosporins and also show high level of resistance to aminoglycosides. Resistance to vancomycin has also become quite common with enterococci, while viridans streptococci are sensitive to vancomycin and vancomycin is the drug of choice for presumptive treatment of viridans grp bacteremia. - Now it is obvious that the infecting organism in this patient is enterococcus as patient has developed bacteremia on central venous line and he is not responding to cephalosporine, aminoglycoside and vancomycin.
Staphylococcus aureus
Viridans streptococci
Enterococcus faecalis
Coagulase negative Staphylococcus