Interactions between Polymorphonuclear Leukocytes and Pseudomonas aeruginosa Biofilms on Silicone Implants In Vivo

Abstract

dChronic infections with Pseudomonas aeruginosa persist because the bacterium forms biofilms that are tolerant to antibiotic treatment and the host immune response. Scanning electron microscopy and confocal laser scanning microscopy were used to visualize biofilm development in vivo following intraperitoneal inoculation of mice with bacteria growing on hollow silicone tubes, as well as to examine the interaction between these bacteria and the host innate immune response. Wild-type P. aeruginosa developed biofilms within 1 day that trapped and caused visible cavities in polymorphonuclear leukocytes (PMNs). In contrast, the number of cells of a P. aeruginosa rhlA mutant that cannot produce rhamnolipids was significantly reduced on the implants by day 1, and the bacteria were actively phagocytosed by infiltrating PMNs. In addition, we identified extracellular wire-like structures around the bacteria and PMNs, which we found to consist of DNA and other polymers. Here we present a novel method to study a pathogen-host interaction in detail. The data presented provide the first direct, high-resolution visualization of the failure of PMNs to protect against bacterial biofilms.

Insulin Treatment Modulates the Host Immune System To Enhance Pseudomonas aeruginosa Wound Biofilms

“…In the chronic wound environment, bacterial necrosis of the short-lived neutrophil occurs consistently and rapidly, and clearance of cellular debris is ineffective (47,48). P. aeruginosa has been shown to lyse neutrophils very quickly in vitro and in vivo through the production of rhamnolipids (24,49). To determine if rhamnolipiddependent lysis of neutrophils enhanced biofilm formation and subsequent tolerance to gentamicin in the diabetic wound environment, we compared gentamicin tolerance in the wounds of mice infected with wild-type P. aeruginosa or a rhamnolipid mutant (PAO1⌬rhlR) (20).…”

“…After 4 days of infection, mice were euthanized and wound tissue sections were extracted and stained for 20 min with 10 M propidium iodide (PI; Invitrogen, Carlsbad, CA) and 2.5 M SYTO 9 (Invitrogen) as previously described (24). PI was used to visualize extracellular DNA and SYTO 9 for visualizing live cells.…”

Chronic Infection by Mucoid Pseudomonas aeruginosa Associated with Dysregulation in T-Cell Immunity to Outer Membrane Porin F

“…Studies in a mouse infection model allowing comparison of PA that was either alginate wild-type, hyperexpressing, or null showed that alginate overexpression was associated with poor bacterial clearance and exacerbated lung pathology, yet with heightened proinflammatory cytokines, that is, raised IFN-g and IL-12 but lower IL-10 in lung homogenates (7). However, in other studies, mucoid or biofilm phenotypes are associated with reduced innate immunity (8,42). …”

Mycobacterium avium Biofilm Attenuates Mononuclear Phagocyte Function by Triggering Hyperstimulation and Apoptosis during Early Infection

“…The same phenomenon in a few other pathogenic bacteria, including Staphylococcus spp. and Enterococcus spp., has been investigated, and it has been generally suggested that biofilms circumvent the typical proinflammatory response from the innate immune system (11)(12)(13)(14). It may be explained by the fact that biofilms are usually encapsulated within exopolysaccharides (EPSs).…”

“…It was recently also reported that polymorphonuclear leukocytes fail to eradicate P. aeruginosa biofilms in vivo (11). Another report indicates that exopolysaccharide (EPS) from Staphylococcus aureus biofilm protects the bacterium from Caenorhabditis elegans immune defense (12).…”