title: Low-pathogenicity Mycoplasma spp. alter human monocyte and macrophage function and are highly prevalent among patients with ventilator-acquired pneumonia.
abstract: Ventilator-acquired pneumonia (VAP) remains a significant problem within intensive care units (ICUs). There is a growing recognition of the impact of critical-illness-induced immunoparesis on the pathogenesis of VAP, but the mechanisms remain incompletely understood. We hypothesised that, because of limitations in their routine detection, Mycoplasmataceae are more prevalent among patients with VAP than previously recognised, and that these organisms potentially impair immune cell function.
  
  
  
  159 patients were recruited from 12 UK ICUs. All patients had suspected VAP and underwent bronchoscopy and bronchoalveolar lavage (BAL). VAP was defined as growth of organisms at >10(4) colony forming units per ml of BAL fluid on conventional culture. Samples were tested for Mycoplasmataceae (Mycoplasma and Ureaplasma spp.) by PCR, and positive samples underwent sequencing for speciation. 36 healthy donors underwent BAL for comparison. Additionally, healthy donor monocytes and macrophages were exposed to Mycoplasma salivarium and their ability to respond to lipopolysaccharide and undertake phagocytosis was assessed.
  
  
  
  Mycoplasmataceae were found in 49% (95% CI 33% to 65%) of patients with VAP, compared with 14% (95% CI 9% to 25%) of patients without VAP. Patients with sterile BAL fluid had a similar prevalence to healthy donor BAL fluid (10% (95% CI 4% to 20%) vs 8% (95% CI 2% to 22%)). The most common organism identified was M. salivarium. Blood monocytes from healthy volunteers incubated with M. salivarium displayed an impaired TNF-α response to lipopolysaccharide (p=0.0003), as did monocyte-derived macrophages (MDMs) (p=0.024). MDM exposed to M. salivarium demonstrated impaired phagocytosis (p=0.005).
  
  
  
  This study demonstrates a high prevalence of Mycoplasmataceae among patients with VAP, with a markedly lower prevalence among patients with suspected VAP in whom subsequent cultures refuted the diagnosis. The most common organism found, M. salivarium, is able to alter the functions of key immune cells. Mycoplasmataceae may contribute to VAP pathogenesis.
authors.affiliation: MRC Centre for Inflammation Research, University of Edinburgh, Edinburgh, UK.
authors.forename: T J
authors.initials: TJ
authors.lastname: Nolan
authors.affiliation: Clinical Microbiology, NHS Lothian, Edinburgh, UK.
authors.forename: N J
authors.initials: NJ
authors.lastname: Gadsby
authors.affiliation: Institute of Cellular Medicine, Newcastle University, Newcastle, UK.
authors.forename: T P
authors.identifier: 0000-0001-5346-7411
authors.initials: TP
authors.lastname: Hellyer
authors.affiliation: Clinical Microbiology, NHS Lothian, Edinburgh, UK.
authors.forename: K E
authors.initials: KE
authors.lastname: Templeton
authors.affiliation: Centre for Infection and Immunity, Queen's University, Belfast, UK.
authors.forename: R
authors.initials: R
authors.lastname: McMullan
authors.affiliation: Department of Microbiology, Belfast Health & Social Care Trust, Belfast, UK.
authors.forename: J P
authors.initials: JP
authors.lastname: McKenna
authors.affiliation: MRC Centre for Inflammation Research, University of Edinburgh, Edinburgh, UK.
authors.forename: J
authors.initials: J
authors.lastname: Rennie
authors.affiliation: MRC Centre for Inflammation Research, University of Edinburgh, Edinburgh, UK.
authors.forename: C T
authors.initials: CT
authors.lastname: Robb
authors.affiliation: MRC Centre for Inflammation Research, University of Edinburgh, Edinburgh, UK.
authors.forename: T S
authors.initials: TS
authors.lastname: Walsh
authors.affiliation: MRC Centre for Inflammation Research, University of Edinburgh, Edinburgh, UK.
authors.forename: A G
authors.initials: AG
authors.lastname: Rossi
authors.affiliation: MRC Centre for Inflammation Research, University of Edinburgh, Edinburgh, UK Division of Anaesthesia, Department of Medicine, University of Cambridge, Cambridge, UK.
authors.forename: A
authors.initials: A
authors.lastname: Conway Morris
authors.affiliation: Institute of Cellular Medicine, Newcastle University, Newcastle, UK.
authors.forename: A J
authors.initials: AJ
authors.lastname: Simpson
mesh_terms: D000368:Aged; D001992:Bronchoalveolar Lavage Fluid / Q000382:microbiology*; D001999:Bronchoscopy; D003428:Cross Infection / Q000382:microbiology*; D005260:Female; D006801:Humans; D007362:Intensive Care Units; D008070:Lipopolysaccharides; D008264:Macrophages / Q000382:microbiology*; D008297:Male; D008875:Middle Aged; D009000:Monocytes / Q000382:microbiology*; D009174:Mycoplasma / Q000472:pathogenicity*; D010587:Phagocytosis; D018410:Pneumonia, Bacterial / Q000382:microbiology*; D053717:Pneumonia, Ventilator-Associated / Q000382:microbiology*; D016133:Polymerase Chain Reaction; D015995:Prevalence; D006113:United Kingdom
chemical_list: D008070:Lipopolysaccharides
keywords: Assisted Ventilation; Bacterial Infection; Cytokine Biology; Innate Immunity; Pneumonia