Methicillin-Resistant Staphylococcus lugdunensis in a neonatal intensive care unit: Diagnostic challenges and emergence of multidrug-resistance

Marianne Hille Smith¹Torunn Gresdal Rønning^2,3Siren Irene Rettedal^4,5Hege Enger²Iren Hoyland Lohr^1,6Jon Sundal⁷Anlaug Vatne⁸Heidi Syre¹Christina Gabrielsen Ås^2,3*

• ¹Department of Medical Microbiology, Stavanger University Hospital, Stavanger, Norway
• ²The Norwegian MRSA Reference Laboratory, Department of Medical Microbiology, Clinic of Laboratory Medicine, St. Olav’s Hospital, Trondheim University Hospital, Trondheim, Norway
• ³Norwegian University of Science and Technology, Department of Clinical and Molecular Medicine, Trondheim, Norway
• ⁴Department of Simulation-based learning, Stavanger University Hospital, Stavanger, Norway
• ⁵Faculty of Health Sciences, University of Stavanger, Stavanger, Norway
• ⁶Department of Clinical Science, University of Bergen, Bergen, Norway
• ⁷Department of Medicine, Stavanger University Hospital, Stavanger, Norway
• ⁸Department of Paediatrics, Stavanger University Hospital, Stavanger, Norway

Abstract Background Staphylococcus lugdunensis is a species within the group of coagulase-negative staphylococci (CoNS), typically regarded as a commensal organism residing on human skin. However, it has increasingly been implicated in a range of clinically significant infections, including bacteremia, particularly in preterm neonates. Notably, S. lugdunensis exhibits sensitivity to a broad spectrum of antibiotics, and methicillin-resistant strains (MRSL) remain uncommon. Aim This study aimed to document the identification of methicillin-resistant S. lugdunensis in an extremely premature neonate, emphasizing the diagnostic challenges in detecting mecA-mediated resistance and characterizing its unusual resistance determinants, while highlighting the implications for outbreak potential in highly vulnerable neonatal intensive care unit populations. Methods Clinical data were collected retrospectively from the patient`s electronic medical journal. MRSL screening and identification were performed with chromogenic media and MALDI-TOF, respectively. Antimicrobial susceptibility testing (AST) was performed according to EUCAST methods, and whole genome sequencing was performed using Illumina and Nanopore technology. Results S. lugdunensis was isolated from nasal sores in an extremely premature neonate. Although initial AST indicated susceptibility to methicillin, a locally introduced area of technical uncertainty prompted further analysis, which led to the detection of mecA by PCR. Screening with chromogenic MRSA plates revealed MRSL colonization in the nose, throat and perineum of the neonate. The MRSL strain belonged to sequence type 3 and displayed an unusual AST profile, caused by SCCmec and a multidrug-resistance plasmid. Conclusions We report a case of MRSL in an extremely premature neonate, which was the index patient in a neonatal intensive care unit outbreak, and highlight the diagnostic challenges faced in detection, screening and AST. Furthermore, we report the unusual antimicrobial susceptibility profile of this MRSL strain, caused by a multidrug-resistance plasmid with potential for transmission among staphylococci.