Species identification of coagulase-negative staphylococcal isolates from blood cultures

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Abstract
Coagulase-negative staphylococci generally are not fully identified, are called Staphylococcus epidermidis and are considered contaminants when isolated from blood cultures. In a cancer hospital during 6 mo., 46 patients had multiple blood cultures (mean, 3.1) which yielded coagulase-negative staphylococci. Species identification of these showed that 10 of the 46 (22%) were not S. epidermidis. Similarly, 96 coagulase-negative staphylococci isolated from only 1 of multiple blood cultures from patients and thought to be skin contaminants were identified. Of 96 of the staphylococci, 14 (16%) of the latter group were not S. epidermidis. Species found included S. haemolyticus, S. hominis, S. warneri, S. simulans and S. xylosus. Eight isolates of these species were methicillin resistant; all 8 were mannitol fermenters. These species evidently infect invasively cancer patients with the same frequency at which the species colonize. No one species was identified as being more pathogenic than the others. Routine species identification of coagulase-negative staphylococci from blood cultures of cancer patients contributed little to management except to occasionally distinguish multiple-episode culture contamination by different species from sustained bacteremia with the same species.