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Padmanabhan Saraswathi, Roger Beuerman; Interaction of Polymorphonuclear neutrophils (PMNs) with Pseudomonas aeruginosa in biofilms in corneal infections in the mouse. Invest. Ophthalmol. Vis. Sci. 2015;56(7 ):4047.
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© ARVO (1962-2015); The Authors (2016-present)
Pseudomonas aeruginosa, is a common ocular pathogen found in cornea infections, often associated with contact lens wear. The survival of this bacteria as a “Biofilm” within a extrapolysaccharide substances sheltered from innate immune defence and antimicrobials. In this study, the interaction of polymorphonuclear neutrophils (PMNs) with Pseudomonas in planktonic and biofilm models was examined using a mouse model of experimental keratitis infection
A suspension (108 CFU/ml) of Pseudomonas aeruginosa (ATTC 9027) was used to infect the mouse cornea (C57BL/6). The infection was monitored by slit lamp. Infected eyes were enucleated at post infection (PI) day1 to describe the planktonic status and PI day3 and 5 for potential biofilm status. The response of polymorphonuclear neutrophils (PMNs) was characterised using histological, ultra-structural imaging and quantifying myeloperoxidase levels
Histology showed the expected large numbers of PMNs in the stroma at PI day1, with diverse morphologies. At later stages of infection they were seen on the corneal surface, but more spherical shape. Scanning Electron Microscopy (SEM) demonstrated the release of Neutrophil Extracellular Traps (NETs) as long fibrils and entangling many bacteria which were seen as free cells at the early stage of infection. However, at PI day3 and 5 the PMNs were seen to change their morphology and lacking pseudopodia appeared immobile, surrounding the clusters of Pseudomonas within a biofilm while other PMNs were on the corneal surface. Transmission Electron Microscopy (TEM) further confirmed the active phagocytosis at PI day1 and immotile PMNs settled beneath the layer of the biofilm at later stages of infection. Enhanced myeloperoxidase activity from 4.1 units at day1 to 16.9 units at day5 PI indicated the increased PMN activity in the course of the infection
The murine neutrophils were seen to be highly activated during an infection and produce NETs as an early defence when the bacteria were planktonic. However, the PMNs were concomitantly sluggish and not successful in phagocytosis when the bacteria developed into biofilms at later times of infection. The early role of PMN NETs as basic host defence may perhaps be considered for novel drug targets to prevent biofilm formation and to augment bacteria killing
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