Pathogenic traits of coagulase-negative Staphylococci and Mammalicoccus isolated from neonatal sepsis blood cultures in low- and middle-income countries.

Coagulase-negative staphylococci (CoNS) are increasingly recognised as neonatal pathogens in low- and middle-income countries (LMICs), yet are often dismissed as contaminants. We characterised the genomic landscape, antimicrobial resistance (AMR), and virulence of 48 CoNS isolates recovered as the sole pathogen from neonates with clinical sepsis across seven hospitals in five LMICs. Whole-genome sequencing determined sequence types, resistomes, and virulomes, whilst virulence was assessed using a Galleria mellonella in vivo model. Species identified included Mammaliicoccus sciuri (n=19; 40%), S. haemolyticus (n=15; 31%), S. epidermidis (n=11; 23%), S. saprophyticus (n=2), and S. xylosus (n=1). M. sciuri predominated in early-onset sepsis (63%); S. haemolyticus (87%) and S. epidermidis (64%) dominated late-onset cases. Multidrug resistance (≥3 classes) was pervasive in S. haemolyticus (93%) and S. epidermidis (91%), with 41.7% of all isolates harbouring mecA-positive SCCmec elements. In Galleria, S. haemolyticus induced significantly higher mortality than S. epidermidis and M. sciuri (p<0.01). Genomically, expanded cap8 capsular gene cassette carriage in S. haemolyticus negatively correlated with pathogenicity (p=0.011), suggesting extensive encapsulation masks acute toxicity. Conversely, S. epidermidis exhibited a broader pathogenic arsenal (adherence, exoenzymes, Type VII secretion), wherein adherence-gene burden positively correlated with mortality (p=0.035), whilst biofilm (icaA-D) carriage showed no significant association (p=0.412). The recovery of these isolates challenges their perception as mere contaminants. Whilst M. sciuri is associated with early-onset disease, the pronounced virulence of S. haemolyticus and the pervasive MDR profiles of both S. haemolyticus and S. epidermidis highlight them as critical, overlooked pathogens in the neonatal unit.