Molecular epidemiology of methicillin-resistant S. aureus in the ICU setting

Abstract

There were 62 MRSA strains from respiratory samples (57; 92 %) or blood (5; 8 %): overall 54 (87 %) HA-MRSA and 8 (13 %) CA-MRSA; respiratory samples accounted for 50 (93 %) and 7 (87.5 %) of HA-MRSA and CA-MRSA strains, respectively. The molecular characterization and spa typing analysis are reported in Table 1: most MRSA had SCCmec II (35 cases, 56.4 %), of which 31 were HA-MRSA. The most common clone was t242 (50 %) and it was associated with SCCmec type II (87 %) and HAMRSA (89 %). All isolates were susceptible to linezolid, whilst 13 and 6 isolates had a minimum inhibitory concentration (MIC) for vancomycin or daptomycin, respectively, above the EUCAST breakpoints for sensitivity. Ten of the t242 strains (32 %) had a vancomycin MIC greater than 2 mg/L, including one with a daptomycin MIC greater than 1 mg/L. The t242 strain represented 77 % (10 out of 13) of MRSA non-sensitive to vancomycin. These strains were further analyzed in order to confirm the high MIC value for vancomycin in a referral microbiology laboratory