Immune evasion by <i>Staphylococcus haemolyticus</i>: Attenuated NET-associated responses and resistance to NET-mediated killing

Mohamed Ahmed; Marwa M. Khalifa; Mohamed Ahmed; Marwa M. Khalifa

doi:10.3934/microbiol.2026021

AIMS Microbiology

2026, Volume 12, Issue 3: 486-507. doi: 10.3934/microbiol.2026021

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Research article

Immune evasion by Staphylococcus haemolyticus: Attenuated NET-associated responses and resistance to NET-mediated killing

Mohamed Ahmed ¹,
Marwa M. Khalifa ^{2
,
,}

1.
College of Medicine, Dhofar University, Salalah 211, Sultanate of Oman
2.
Department of Microbiology and Immunology, Faculty of Pharmacy, Assiut University, Assiut, Egypt

Received: 12 April 2026 Revised: 18 June 2026 Accepted: 03 July 2026 Published: 27 July 2026

Neutrophil extracellular traps (NETs) contribute to innate immune defense by trapping and exposing microorganisms to DNA-associated antimicrobial proteins. However, some pathogens can tolerate NET-associated antimicrobial activity and persist within the host. Staphylococcus haemolyticus is an emerging multidrug-resistant coagulase-negative staphylococcal pathogen associated with healthcare-related infections, but its interaction with neutrophil-mediated defenses remains poorly understood. This study investigated whether a multidrug-resistant clinical S. haemolyticus isolate modulates neutrophil antimicrobial activity and NET-associated responses, using a clinical Staphylococcus aureus isolate as a comparator. Extracellular DNA release and NET-associated structures were assessed by fluorescence microscopy, scanning electron microscopy, fluorometric DNA quantification, microscopic enumeration, and MPO-DNA complex ELISA. The tested S. haemolyticus isolate induced extracellular DNA release and MPO-DNA complex formation; however, these responses were lower than those induced by PMA and were attenuated compared with the S. aureus comparator. S. haemolyticus also showed reduced susceptibility to neutrophil-mediated killing and greater resistance to NET-mediated killing than S. aureus. NE and MPO mRNA expression was not significantly altered following bacterial exposure. Collectively, these findings provide initial evidence that a clinical S. haemolyticus isolate can induce attenuated NET-associated responses while resisting NET-mediated antimicrobial activity, highlighting a potential immune-evasion mechanism in this emerging opportunistic pathogen.
Citation: Mohamed Ahmed, Marwa M. Khalifa. Immune evasion by Staphylococcus haemolyticus: Attenuated NET-associated responses and resistance to NET-mediated killing[J]. AIMS Microbiology, 2026, 12(3): 486-507. doi: 10.3934/microbiol.2026021

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Abstract

Neutrophil extracellular traps (NETs) contribute to innate immune defense by trapping and exposing microorganisms to DNA-associated antimicrobial proteins. However, some pathogens can tolerate NET-associated antimicrobial activity and persist within the host. Staphylococcus haemolyticus is an emerging multidrug-resistant coagulase-negative staphylococcal pathogen associated with healthcare-related infections, but its interaction with neutrophil-mediated defenses remains poorly understood. This study investigated whether a multidrug-resistant clinical S. haemolyticus isolate modulates neutrophil antimicrobial activity and NET-associated responses, using a clinical Staphylococcus aureus isolate as a comparator. Extracellular DNA release and NET-associated structures were assessed by fluorescence microscopy, scanning electron microscopy, fluorometric DNA quantification, microscopic enumeration, and MPO-DNA complex ELISA. The tested S. haemolyticus isolate induced extracellular DNA release and MPO-DNA complex formation; however, these responses were lower than those induced by PMA and were attenuated compared with the S. aureus comparator. S. haemolyticus also showed reduced susceptibility to neutrophil-mediated killing and greater resistance to NET-mediated killing than S. aureus. NE and MPO mRNA expression was not significantly altered following bacterial exposure. Collectively, these findings provide initial evidence that a clinical S. haemolyticus isolate can induce attenuated NET-associated responses while resisting NET-mediated antimicrobial activity, highlighting a potential immune-evasion mechanism in this emerging opportunistic pathogen.

Conflict of interest

The authors declare that they have no conflicts of interest.

Author contributions

Mohamed Ahmed: Conceptualization, study design, methodology, formal analysis, interpretation of results and visualization. Marwa M. Khalifa: Conceptualization, methodology, investigation, data curation, validation, supervision and project administration. Both authors participated in writing, reviewing and editing of the manuscript.

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