September 17, 20250 citationsOpen Access

Molecular characterization of methicillin-resistant Staphylococcus aureus isolates from a tertiary pediatric hospital in southern Brazil

ÉSÉrika Medeiros dos SantosHospital Erasto Gaertner DKDamaris KrulInstituto de Tecnologia do Paraná TVThaís Muniz VasconcelosUniversidade Iguaçu

Key Points

MRSA isolates showed 100% sensitivity to vancomycin and linezolid, indicating effective treatment options.
Two SCCmec types were prevalent, with types IV and II representing over 95% of total isolates.
Whole genome sequencing demonstrated polyclonal spread of MRSA across multiple sequence types, underscoring diversity.
CA-MRSA strains were found to cause significant infections, with CC5 being the dominant clone in this pediatric setting.

Abstract

Methicillin-resistant Staphylococcus aureus (MRSA) is a leading cause of hospital- and community-acquired infections (HA-MRSA and CA-MRSA, respectively). Although this microorganism is associated with childhood bacteremia, its epidemiology and predictive factors are not well established. In this study, the susceptibility profiles and molecular characteristics of 46MRSA isolates obtained from blood samples and other sterile fluids of pediatric patients between January 2017 and May 2022 were characterized. The isolates were identified using matrix-assisted laser desorption ionization-time of flight mass spectrometry. After that, their antimicrobial susceptibility profiles were assessed trough broth microdilution, and their molecular characteristics was performed by whole genome sequencing. Antibiotic susceptibility tests showed that the isolates were 100% sensitive to vancomycin, linezolid, and sulfamethoxazole-trimethoprim. In terms of SCCmec, types IV and II were the most prevalent, accounting for 47.82% (22/44) and 47.72% (21/44) of the isolates, respectively, whereas type I was identified in just one isolate (2.27%). Thus, 50% of infections were caused by CA-MRSA and HA-MRSA. Sequencing analysis revealed polyclonal spread, with several sequence types (STs) identified. Five STs belonging to the CC5 clonal complex (ST5, ST105, ST1649, ST1176, and ST1307) accounted for most of the isolates (n=38). The detected virulence genes were sak, tst-1, ACME, hlgA, lukF-PV/lukS-PV, and lukD/lukE. The Panton–Valentine Leukocidin (PVL) toxin gene was found in nine isolates, all of which were CA-MRSA and carried SCCmec type IV. Several antimicrobial resistance genes encoding resistance to different antibiotic classes were identified. In conclusion, we conclude that CA-MRSA strains are currently ubiquitous in hospital environments, causing serious infections, with CC5 being predominant over the past five years.

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