# Methicillin-resistant Staphylococcus lugdunensis in a neonatal intensive care unit: diagnostic challenges and emergence of multidrug-resistance

## TL;DR

This paper reports a rare case of methicillin-resistant Staphylococcus lugdunensis in a premature baby and its potential to cause outbreaks in neonatal units.

## Contribution

The study identifies a multidrug-resistant strain of S. lugdunensis in a neonate and highlights diagnostic challenges and outbreak risks.

## Key findings

- Methicillin-resistant S. lugdunensis was detected in a premature neonate using PCR and chromogenic media.
- The strain carried SCCmec and a multidrug-resistance plasmid, leading to an unusual antibiotic resistance profile.
- The case triggered an outbreak in the neonatal intensive care unit, emphasizing transmission risks.

## Abstract

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.

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.

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.

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.

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.