Abstract
BackgroundSerratia marcescens is a gram-negative bacterium and often causes nosocomial infections. There have been few studies of the virulence factors of this bacterium. The only S. marcescens hemolytic and cytotoxic factor reported, thus far, is the hemolysin ShlA.ResultsAn S. marcescens shlAB deletion mutant was constructed and shown to have no contact hemolytic activity. However, the deletion mutant retained hemolytic activity on human blood agar plates, indicating the presence of another S. marcescens hemolytic factor. Functional cloning of S. marcescens identified a phospholipase A (PhlA) with hemolytic activity on human blood agar plates. A phlAB deletion mutant lost hemolytic activity on human blood agar plates. Purified recombinant PhlA hydrolyzed several types of phospholipids and exhibited phospholipase A1 (PLA1), but not phospholipase A2 (PLA2), activity. The cytotoxic and hemolytic activities of PhlA both required phospholipids as substrates.ConclusionWe have shown that the S. marcescens phlA gene produces hemolysis on human blood agar plates. PhlA induces destabilization of target cell membranes in the presence of phospholipids. Our results indicated that the lysophospholipids produced by PhlA affected cell membranes resulting in hemolysis and cell death.
Highlights
Serratia marcescens is a gram-negative bacterium and often causes nosocomial infections
S. marcescens showed contactdependent hemolytic activity on human red blood cells (RBC), which was greater for bacteria grown at 30°C than at 37°C (Fig. 1B)
There are no data about a phospholipase A (PhlA) hemolytic activity, since some other phospholipases have hemolytic activity, we investigated whether the S. marcescens phlA gene product might be a hemolysin
Summary
Serratia marcescens is a gram-negative bacterium and often causes nosocomial infections. S. marcescens pathogenicity is poorly understood, its extracellular secreted enzymes, including several types of proteases, are candidates for virulence factors [2]. Hemolysins are produced by various pathogenic bacteria and have been proposed to be responsible for their pathogenesis [4,5,6]. These hemolysins, including S. marcescens (page number not for citation purposes). ShlA has been shown to increase cell membrane permeability, but not to form an oligomer [3]. Another type of hemolysin has phospholipase C (PLC) activity. The cytotoxic and hemolytic activities of these enzymes have remained unclear, and the importance of PLA in bacterial virulence is not well understood
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