Co-infection by two linezolid-resistant coagulase-negative staphylococci with two different resistance determinants.

Linezolid resistance among Gram-positive pathogens is being reported with increasing frequency. We examined 14 linezolid-resistant coagulase-negative staphylococci (CoNS) isolated from blood cultures obtained from patients admitted to the Intensive Care Unit of Vicenza General Hospital, Italy. The species identification yielded 10 Staphylococcus epidermidis, 3 Staphylococcus hominis, and 1 Staphylococcus capitis. Minimal inhibitory concentrations of linezolid ranged between 16 and 32 mg/l. By sequencing domain V of the 23S rRNA gene, 4 isolates were found to harbour a G2576T mutation and 10 isolates a G2447T mutation. None of the strains under study presented either the cfr gene or cardinal mutations in the L3, L4, or L22 riboproteins. In this clinical collection of linezolid-resistant CoNS the G2447T mutation was dominantly associated with S. epidermidis, while the G2576T mutation was found in other CoNS species. Two different CoNS species endowed with either mutation were isolated from 2 patients.