Gram Positive Cocci
Blood culture from a febrile patient has growth of gram + ve cocci. Further testing revealed that the isolate possessed the group D antigen, was not betalactamase-positive, but was resistant to vancomycin. Which of the following is the most likely identification of this isolate?(AIPG 2012)
A gram-positive coccus resistant to penicillin must be assumed to be enterococcus until other, more definitive biochemical testing places the isolate in one of the more esoteric groups of gram-positive cocci.
However, penicillin-resistant, non-beta-lactamase-producing, vancomycin-resistant, gram-positive cocci are most likely E. faecium.
Vancomycin resistance is less often seen in E.faecalis in comparison to E.faecium.
There are a variety of mechanisms for vancomycin resistance in E. faecium and they have been termed Van A, B, or C. These isolates have become one of the most feared nosocomial pathogens in the hospital environment.
Unfortunately, no approved antibiotics can successfully treat vancomycin-resistant enterococci (VRE)-only some experimental antibiotics such as Synercid.
a. Pairs of flame-shaped / lanceolate cocci, 1m diameter
b. Capsulated – India ink, quellung reaction
c. Aerobe, facultative anaerobe, capnophilic, temp 37c , pH 7.4, grows on enriched media
d. Blood agar: 0.5-1mm, moist, mucoid, transparent colonies. Zone of hemolysis; further incubation draughtsman colony. Anaerobic conditions- hemolysis (Pneumolysin)
e. Ferment glucose, sucrose, lactose, inulin acid no gas
f. Bile soluble: activates autolytic enzymes
g. Optochin sensitive
h. Most important virulence factor-polysaccharide capsule.