Methicillin-resistant Staphylococcus epidermidis isolates with reduced vancomycin susceptibility from bloodstream infections in a neonatal intensive care unit

Vancomycin has become the first-line therapy for most infections caused by methicillin-resistant staphylococci. To evaluate the vancomycin MIC, staphylococcal cassette chromosome (SCC ) types and clonality of coagulase-negative staphylococci (CoNS) isolates recovered from neonates with true primary bloodstream infections (BSI). CoNS isolates were prospectively recovered from blood cultures of non-repetitive patients admitted to a neonatal intensive care unit (NICU) in a tertiary-care hospital during a 3-year period. BSI was defined based on established criteria. Micro-organisms were identified phenotypically and by PCR. MIC-values for vancomycin and oxacillin were determined by broth dilution method and E-test. The SCC type conferring methicillin resistance was determined by multiplex PCR. The heterogeneous vancomycin (hV) resistance phenotype was screened on brain heart infusion agar containing 4 µg ml of vancomycin. The clonality was investigated by PFGE. Seventy-four CoNS isolates were recovered from blood cultures of neonates during the study period but only 40 (54 %) were associated with true primary BSI. Nine (22.5%) babies died. was the most prevalent species (95 %; 38/40). All isolates were methicillin-resistant (MR). SCC type IV was predominant (55.3 %; 21/38). Most (80.0 %; 32/38) isolates exhibited vancomycin MIC-values of 2-4 µg ml not associated with the SCC type or clonality. Sixteen (42.1%) isolates displayed hV resistance. All babies who died were harbouring MR- exhibiting vancomycin MICs of 2-4 µg ml . The findings of this study demonstrated that blood invasive MR- isolates recovered at NICU tend to show decreased vancomycin susceptibility making therapy of those fragile patients difficult.