Thermonucleases Contribute to Staphylococcus aureus Biofilm Formation in Implant-Associated Infections–A Redundant and Complementary Story

Abstract

Biofilms formed by Staphylococcus aureus are one of the predominant causes of implant-associated infections (IAIs). Previous studies have found that S. aureus nucleases nuc1 and nuc2 modulate biofilm formation. In this study, we found low nuc1/nuc2 expression and high biofilm-forming ability among IAI isolates. Furthermore, in a mouse model of exogenous IAIs, Δnuc1/2 exhibited higher bacterial load on the surface of the implant than that exhibited by the other groups (WT, Δnuc1, and Δnuc2). Survival analysis of the hematogenous IAI mouse model indicated that nuc1 is a virulence factor related to mortality. We then detected the influence of nuc1 and nuc2 on biofilm formation and immune evasion in vitro. Observation of in vitro biofilm structures with scanning electron microscopy and evaluation of bacterial aggregation with flow cytometry revealed that both nuc1 and nuc2 are involved in biofilm structuring and bacterial aggregation. Unlike nuc1, which is reported to participate in immune evasion, nuc2 cannot degrade neutrophil extracellular traps. Moreover, we found that nuc1/nuc2 transcription is negatively correlated during S. aureus growth, and a possible complementary relationship has been proposed. In conclusion, nuc1/nuc2 are complementary genes involved in biofilm formation in exogenous IAIs. However, nuc2 contributes less to virulence and is not involved in immune evasion.

Micrococcal Nuclease stimulates Staphylococcus aureus Biofilm Formation in a Murine Implant Infection Model

“…Apparently, Nuc1 is important for S. aureus biomaterial-associated infection to persist in the acute phase of the foreign body reaction and even extends it, which was also indicated by the lack of foreign body giant cells in mice with the inoculated wildtype strain ( Table 1 ) corroborating earlier observations in biomaterial-associated infection studies ( van Putten et al., 2011 ; Sheikh et al., 2015 ). A recent study also showed that Nuc1 activity contributed to S. aureus survival in a hematogenous implant-associated infection model even though Nuc1 had no influence on the bacterial load in peri implant tissue or adherent bacteria on the implant and only nuc1 and nuc2 double mutants impacted bacterial load ( Yu et al., 2021 ). This discrepancy in the effect of Nuc1 on in-vivo bacterial survival may be due to differences in utilized clinical strain, inoculum concentration, site of implantation and type of biomaterial.…”

Genetic relationship of Staphylococcus aureus isolated from humans, animals, environment, and Dangke products in dairy farms of South Sulawesi Province, Indonesia

“…The chromosome of S. aureus encodes thermonucleases, nuc gene. The nuc gene is known as a specific virulence factor in S. aureus [36], and it contributes to biofilm formation [37] and immune evasion [38].…”

Molecular Prerequisites for Neutrophil Extracellular Trap Formation and Evasion Mechanisms of Staphylococcus aureus

“…However, NETs often fail to eradicate replicating S. aureus during persistent infections as this pathogen releases a plethora of virulence factors into the extracellular milieu that antagonize NET-mediated entrapment and killing ( Table 1 ) ( 79 ). For example, S. aureus secretes a robust thermonuclease (Nuc) which rapidly dismantles NETs thereby affecting local, systemic, as well as chronic infections ( Figure 1 ) ( 14 , 16 , 17 , 34 , 59 ). In that regard, we note that Nuc-mediated degradation of NETs may further restrict the communication of PMNs and macrophages ( 34 ).…”