Pseudomonas aeruginosa Forms Biofilms in Acute Infection Independent of Cell-to-Cell Signaling

Abstract

Biofilms are bacterial communities residing within a polysaccharide matrix that are associated with persistence and antibiotic resistance in chronic infections. We show that the opportunistic pathogen Pseudomonas aeruginosa forms biofilms within 8 h of infection in thermally injured mice, demonstrating that biofilms contribute to bacterial colonization in acute infections as well. Using light, electron, and confocal scanning laser microscopy, P. aeruginosa biofilms were visualized within burned tissue surrounding blood vessels and adipose cells. Although quorum sensing (QS), a bacterial signaling mechanism, coordinates differentiation of biofilms in vitro, wild-type and QS-deficient P. aeruginosa strains formed similar biofilms in vivo. Our findings demonstrate that P. aeruginosa forms biofilms on specific host tissues independently of QS.Bacterial biofilms are communities of microorganisms residing within a polysaccharide matrix that have been imaged in dental plaques, medical prostheses, and contact lenses (7,31,33). It is well accepted that biofilms play important roles in bacterial persistence and antibiotic resistance in chronic infections, such as cystic fibrosis and otitis media (3,8,9,30). However, the existence and/or roles of biofilms in acute infections, which are defined by short time courses and high severity, have not been examined. The opportunistic gram-negative pathogen Pseudomonas aeruginosa causes both chronic and acute infections and is one of the leading causes of morbidity and mortality in thermally injured patients (27,37). In this study we examined the production of P. aeruginosa biofilms in the thermally injured mouse model of acute infections.The differentiation or maturation of P. aeruginosa biofilms in vitro depends on intercellular signaling systems or quorum sensing (QS) (5,22). QS systems in many gram-negative bacteria rely on acylated homoserine lactones (AHLs), which are produced at high levels when cell density is high and act as ligands for transcriptional regulators. The P. aeruginosa synthases LasI and RhlI synthesize two AHLs, N-3-oxododecanoyl homoserine lactone (3OC 12 -HSL) and N-butyryl-homoserine lactone (C 4 -HSL), which bind and modulate the activity of the transcriptional regulators LasR and RhlR, respectively (28). These transcriptional regulators then regulate the transcription of many genes whose products, including proteases, elastases, toxins, and hemolysins, are thought to be crucial for virulence (28). P. aeruginosa strains lacking functional QS systems are less virulent than wild-type strains (29) and form flat, undifferentiated biofilms on glass surfaces (5). These undifferentiated biofilms are less stable than the differentiated biofilms formed by wild-type P. aeruginosa as they can be easily disrupted by the detergent sodium dodecyl sulfate (5). However, the role of QS in biofilm formation has not previously been examined in vivo. Therefore, in this study we have also examined the role of QS in P. aeruginosa biofilm formation in the acute infection model. ...

Garlic ointment inhibits biofilm formation by bacterial pathogens from burn wounds

“…2b). Quantitative analysis of the biofilm using the COMSTAT program revealed a biomass (35.35 mm 3 per mm 2 ), mean thickness (120.79 mm) and surface area (2.15610 7 mm 2 ) similar to P. aeruginosa biofilms in the flow-through continuous-culture system (Schaber et al, 2007) and S. aureus AH133 biofilms on haemodialysis catheters in vivo (Tran et al, 2012). Quantification of the bacteria present showed a 4-5 log increase in the number of micro-organisms from 10 3 -10 4 c.f.u.…”

“…James et al (2008) reported the formation of polymicrobial biofilms within chronic wounds such as foot ulcers, venous leg ulcers and pressure ulcers. Additionally, using the murine model of thermal injury, Schaber et al (2007) described the formation of a P. aeruginosa biofilm within injured/infected tissues. Furthermore, Kennedy et al (2010) recently analysed multiple biopsies from numerous burn wounds and reported the presence of bacterial biofilms within the ulcerated areas of these wounds.…”

Microorganisms in metalworking fluids: Current issues in research and management

“…The process of biofilm formation is quite fast; even in human tissues where several immune mechanisms exist to efficiently eradicate bacteria, the mature biofilm can develop within eight hours (e.g. in burn wound) [37]. The formation of biofilm in metalworking fluids is so far unknown process; therefore, the duration of the process of biofilm formation in these environments still needs to be elucidated.…”

Influence of Quorum Sensing and Iron on Twitching Motility and Biofilm Formation in Pseudomonas aeruginosa

“…Details of in vivo P. aeruginosa biofilm formation, structure, and properties are limited, with most of our understanding of these structures coming from the study of model biofilms formed in vitro (3,15,29,30,56,80,81,84). In vitro biofilm development in P. aeruginosa is characterized by bacterial surface attachment, followed by microcolony formation by clonal expansion or motility-driven cell-to-cell aggregation and subsequent formation of a flat, uniform, confluent biofilm or heterogeneous, structured biofilms characterized by cell aggregates or "mushroom" structures separated by channels or spaces (38,40).A number of studies have linked quorum sensing (QS), cell density control of gene expression involving acylhomoserine lactones (acyl-HSLs) (36, 69), and biofilm formation/development in P. aeruginosa (17,26,38,64), although some studies indicate that QS has little or no role, with QS mutants being proficient in biofilm formation (27,62,67,68). These discrepancies are generally linked to differences in biofilm model and/or culture conditions, and indeed, a recent study confirmed that the QS dependence of biofilm formation is nutritionally conditional (i.e., QS systems are needed for biofilm formation in some growth media [e.g., succinate] but not others [e.g., glucose or glutamate]) (73).…”