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Updated: Mar 26, 2026
Quantifying the Cytotoxicity of Staphylococcus aureus Against Human Polymorphonuclear Leukocytes
Published on: January 3, 2020
Bactericidal effects of polyhexamethylene biguanide against intracellular Staphylococcus aureus EMRSA-15 and USA 300
Nor Fadhilah Kamaruzzaman1, Rebuma Firdessa2, Liam Good3
1Department of Pathology and Pathogen Biology, Royal Veterinary College, University of London, Royal College Street, London NW1 0TU, UK Faculty of Veterinary Medicine, Universiti Malaysia Kelantan, Locked Bag 36, Pengkalan Chepa, 16100 Kota Bharu, Kelantan, Malaysia.
Objectives:
The treatment of skin infections caused by Staphylococcus aureus is limited by acquired antibiotic resistance and poor drug delivery into pathogen and host cells. Here, we investigated the antibacterial activities of six topically used antimicrobials and a cationic polymer, polyhexamethylene biguanide (PHMB), against intracellular MSSA strain RN4420 and MRSA strains EMRSA-15 and USA 300.
Methods:
The MICs of antimicrobials were determined for MSSA and MRSA strains, and the bactericidal activities of nadifloxacin and PHMB against intracellular MRSA were determined using infected keratinocytes. Fluorescein-tagged PHMB (PHMB-FITC) was used to study PHMB uptake, co-localization with intracellular EMRSA-15 and retention in keratinocytes. The mechanism(s) of PHMB uptake into keratinocytes were studied using a dynamin inhibitor, dynasore.
Results:
Gentamicin, nadifloxacin and PHMB showed the lowest MICs for MRSA. Nadifloxacin at 10 mg/L killed 80% of intracellular EMRSA-15, but was not effective against USA 300. PHMB at 4 mg/L killed almost 100% of intracellular EMRSA-15 and USA 300. PHMB entered keratinocytes, co-localized with intracellular EMRSA-15 and was retained by the cells for over 5 h. PHMB uptake and its intracellular antibacterial activities were inhibited by the dynamin inhibitor, dynasore.
Conclusions:
PHMB kills intracellular MRSA via direct interaction with pathogens inside keratinocytes and host cell entry is dynamin dependent.
Insights
Polyhexamethylene biguanide (PHMB) effectively kills intracellular methicillin-resistant Staphylococcus aureus (MRSA) in skin cells. This novel approach utilizes dynamin-dependent host cell entry for enhanced antibacterial activity against resistant strains.
Area of Science:
- Microbiology
- Dermatology
- Pharmacology
Background:
- Antibiotic resistance in Staphylococcus aureus, particularly MRSA, poses a significant challenge for treating skin infections.
- Limited drug delivery into host and pathogen cells hinders effective treatment of intracellular bacterial infections.
Purpose of the Study:
- To investigate the antibacterial activities of topical antimicrobials and polyhexamethylene biguanide (PHMB) against intracellular Staphylococcus aureus strains.
- To evaluate the efficacy of PHMB in eliminating intracellular MRSA within keratinocytes.
Main Methods:
- Minimum inhibitory concentrations (MICs) of antimicrobials were determined for MSSA and MRSA.
- Bactericidal activity against intracellular MRSA was assessed using infected keratinocytes.
- PHMB uptake, co-localization, and retention in keratinocytes were studied using fluorescently tagged PHMB (PHMB-FITC).
- Dynamin-dependent endocytosis was investigated using the inhibitor dynasore.
Main Results:
- PHMB demonstrated low MICs against MRSA strains.
- PHMB effectively killed nearly 100% of intracellular MRSA (EMRSA-15 and USA 300) at 4 mg/L.
- PHMB entered keratinocytes, co-localized with intracellular bacteria, and was retained for over 5 hours.
- PHMB uptake and intracellular activity were inhibited by dynasore, indicating dynamin-dependent entry.
Conclusions:
- PHMB exhibits potent bactericidal activity against intracellular MRSA within keratinocytes.
- Host cell entry of PHMB is dependent on dynamin-mediated endocytosis.
- PHMB offers a promising therapeutic strategy for intracellular MRSA skin infections.
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