The Major Extracellular Protease of the Nosocomial Pathogen Stenotrophomonas maltophilia

Abstract

Stenotrophomonas maltophilia is increasingly emerging as a multiresistant pathogen in the hospital environment. In immunosuppressed patients, these bacteria may cause severe infections associated with tissue lesions such as pulmonary hemorrhage. This suggests proteolysis as a possible pathogenic mechanism in these infections. This study describes a protease with broad specificity secreted by S. maltophilia. The gene, termed StmPr1, codes for a 63-kDa precursor that is processed to the mature protein of 47 kDa. The enzyme is an alkaline serine protease that, by sequence homology and enzymic properties, can be further classified as a new member of the family of subtilases. It differs from the classic subtilisins in molecular size, in substrate specificity, and probably in the architecture of the active site. The StmPr1 protease is able to degrade several human proteins from serum and connective tissue. Furthermore, pan-protease inhibitors such as ␣ 1 -antitrypsin and ␣ 2 -macroglobulin were unable to abolish the activity of the bacterial protease. The data support the interpretation that the extracellular protease of S. maltophilia functions as a pathogenic factor and thus could serve as a target for the development of therapeutic agents.Stenotrophomonas maltophilia, formerly referred to as Xanthomonas maltophilia or Pseudomonas maltophilia (1, 2), is an aerobic nonfermentative Gram-negative bacterium of widespread occurrence. For healthy humans, it is regarded as an opportunistic germ; it has been implicated in a variety of infections without distinctive clinical features (for a review, see Ref.3). However, in immune-compromised patients, particularly those with bone marrow aplasia or receiving intensive chemotherapy, cases of fulminant hemorrhagic pneumonia have been reported, even with fatal outcome (4 -6). In patients not surviving infections with S. maltophilia, histological inspection of the lung tissue revealed massive bleeding caused by damage to the lung epithelium (4). There are further reports demonstrating involvement of this bacterium in massive hemorrhagic processes of the small intestine and the subclavian artery accompanied by severe lesions of the tissue (5, 6). These observations strongly suggest the participation of proteolytic activity, produced by the bacteria, which may damage the infected tissue. Indeed, it is known that members of the Pseudomonaceae express and secrete a variety of proteases (cf. Ref. 7). Whereas the primary function of these enzymes is to provide a source of free amino acids for bacterial survival and growth, there is accumulating evidence that bacterial proteases may play a pathogenic role in the infected host by involvement in tissue invasion and destruction, evasion of host defenses, and modulation of the host immune system (8).The broad administration of antibiotics currently applied in cases of intensive care patients leads to selection of multiresistant S. maltophilia strains. Consequently, these bacteria are found with increasing frequency in the hospital environmen...

Stenotrophomonas maltophilia infection in hematopoietic SCT recipients: high mortality due to pulmonary hemorrhage

“…In vitro data demonstrated that S. maltophilia produces proteases, which can break down the protein components of collagen, fibronectin and fibrinogen, 31,32 and this may contribute to local tissue damage and hemorrhage. 1 Because our present histopathological findings at autopsy demonstrated alveolar hemorrhage and the massive infiltration of Gram-negative rods in lungs without invasion by neutrophils or lymphocytes, S. maltophilia itself might damage lung tissue, which leads to pulmonary hemorrhage.…”

Molecular Characterization of Virulence Determinants of Stenotrophomonas Maltophilia Strains Isolated from Patients Affected by Cystic Fibrosis

“…Oligonucleotides PrL (5'-CGAGAACGACAACGAGTGCTACA-3') and PrR (5'-CACGGCGGTCTTGTTGGTCA-3') were used to amplify a 0.9 kb internal fragment of the StmPrl gene (GenBank accession no. AJ291488) (13). Both DNA probes were labeled with a-p 32 dATP by the random priming method (Amersham Kit), and Southern hybridization was performed according to Sambrook and Russel (14).…”

Screening of Protease Inhibitory Activity in Aqueous Extracts of Marine Invertebrates from Cuban Coast

“…It is important to note that in the case of C. muricatus, a molecule with inhibitory activity against subtilisin in the submicromolar level, CmPI-2, has been already isolated [25]. Subtilisins are present in many pathogenic microorganisms required within invasion/proliferation processes [7] [8]. Marine invertebrates live alongside many bacteria and parasites in aquatic environments and they protect themselves against pathogenic infection through their innate immune system, which utilizes several biomolecules for their defense including protease inhibitors [22].…”

“…the serine proteases human neutrophil elastase (HNE), subtilisins, dipeptidylpeptidase-IV (DPPIV) and papain-like proteases, such as cathepsin K. The former, which is involved in pulmonary emphysema, rheumatoid arthritis and cystic fibrosis, is released from human polymorphonuclear leukocytes in response to inflammatory stimuli and it is responsible for the degradation of connective tissue proteins [5] [6]. Subtilisins are involved in invasion processes of many pathogenic parasites and bacteria, such as Plasmodium falciparum and the nosocomial pathogen Stenotrophomonas maltophilia, [7] [8]. Dipeptidylpeptidase-IV is implicated in human systemic conditions, such as diabetes mellitus, cancer and inflammatory diseases [9] [10].…”