Pandemic clone USA300 in a Brazilian hospital: detection of an emergent lineage among methicillin-resistant Staphylococcus aureus from bloodstream infections

Background: Staphylococcus aureus is one of the leading causes of bloodstream infections (BSI) worldwide. In Brazil, the hospital-acquired methicillin-resistant S. aureus USA100/SCC mec II lineage replaced previously well-established clones. However, the isolation of community-associated (CA) MRSA lineages from hospitalized patients is an increasing issue. Methods Consecutive S. aureus isolates recovered from BSI episodes of patients admitted between January 2016 and December 2018 in a Brazilian teaching hospital were tested for antimicrobial resistance, characterized as their genotypic features and the clinical characteristics of the patients were evaluated. Results A total of 123 S. aureus isolates were recovered from 113 patients. All isolates were susceptible to linezolid, teicoplanin and vancomycin and 13.8% were non-susceptible for daptomycin. Vancomycin MIC 50 and MIC 90  = 2 mg/L was found for both MRSA and MSSA isolates. MRSA isolation rate was 30.1% (37/123), and 51.4% of them carried the SCC mec II, followed by SCC mec IV (40.5%). Among the 37 MRSA isolates, the main lineages found were USA100/SCC mec II/ST5 and ST105 (53.7%) and USA800/ST5/SCC mec IV (18.9%). Surprisingly, were detected six (16%) CA MRSA isolates belonged to USA300/ST8/SCC mec IVa and carrying pvl genes and ACME cassette type I. These patients with USA300 BSI had severe comorbidities, including cancer, most had a Charlson score ≥ 5 and attended wards where health professionals were shared. MRSA isolates were associated with hospital acquired infections ( p  = 0.02) in older patients ( p  = 0.03) and those diagnosed with hematologic cancer ( p  = 0.04). A total of 52 (46%) patients died, and 60% of them presented a MRSA BSI. Conclusions Pandemic MRSA USA300 was detected for the first time in our hospital, and we hypothesized its cross-transmission between patients with BSI. This lineage can be already circulating among Brazilian hospitals, highlighting the importance of surveillance programs to fight multidrug resistant and hypervirulent isolates.