Urokinase enhances the growth of Pseudomonas spp. in vitro under nonshaking (oxygen limited) conditions

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Abstract
Urokinase is a proteinase that normally functions as a plasminogen activator. It is detected in a number of tissues and can be expressed by inflammatory cells such as macrophages and polymorphonuclear leucocytes. Addition of human urokinase to cultures of mucoid or nonmucoid variants of Pseudomonas aeruginosa (strain PAO and clinical isolates from patients with cystic fibrosis) or Pseudomonas cepacia incubated in a minimal medium under nonshaking (oxygen limited) conditions led to dose-dependent enhancement of bacterial growth. The enzyme exhibited a minimal effect on the growth of bacteria when cultured under more intense aeration conditions. This enhancement of bacterial growth by urokinase required the presence of active enzyme and was not detected with inactivated enzyme or noncatalytic domains of the enzyme. Enhancement of bacterial growth was not observed following incubation of P. aeruginosa with other proteinases including thrombin, neutrophil elastase, trypsin, chymotrypsin, or pseudomonas elastase and pseudomonas alkaline proteinase. Therefore, the observed effect of urokinase was relatively specific for this enzyme. As urokinase is a natural constituent of the lung, this enzyme could contribute to bacterial growth during pulmonary infections, particularly in an inflammatory environment in which the oxygen tension may be reduced.Key words: plasminogen activators, Pseudomonas aeruginosa, bacterial growth, urokinase, host proteinases.

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