title: Bactericidal effects of polyhexamethylene biguanide against intracellular Staphylococcus aureus EMRSA-15 and USA 300.
abstract: OBJECTIVE
  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.
authors.affiliation: Department 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.
authors.forename: Nor Fadhilah
authors.initials: NF
authors.lastname: Kamaruzzaman
authors.affiliation: Institute for Molecular Infection Biology, Josef-Schneider-Str. 2/D15, University of Würzburg, 97080 Würzburg, Germany.
authors.forename: Rebuma
authors.initials: R
authors.lastname: Firdessa
authors.affiliation: Department of Pathology and Pathogen Biology, Royal Veterinary College, University of London, Royal College Street, London NW1 0TU, UK lgood@rvc.ac.uk.
authors.forename: Liam
authors.initials: L
authors.lastname: Good
mesh_terms: D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D001645:Biguanides / Q000494:pharmacology*; D002460:Cell Line; D024841:Fluoroquinolones / Q000494:pharmacology; D006801:Humans; D015603:Keratinocytes / Q000382:microbiology; D008826:Microbial Sensitivity Tests; D050296:Microbial Viability / Q000187:drug effects*; D011807:Quinolizines / Q000494:pharmacology; D013211:Staphylococcus aureus / Q000187:drug effects* / Q000502:physiology
chemical_list: D000900:Anti-Bacterial Agents; D001645:Biguanides; D024841:Fluoroquinolones; D011807:Quinolizines; C031233:polihexanide; C062127:nadifloxacin