Utilization of Transferrin-Bound Iron by Medically Important Staphylococcal Species

Staphylococcus aureus is able to utilize efficiently transferrin-bound iron as an iron source, whereas other staphylococci are not. The reason for this difference remains unclear. We compared the activity of siderophore-mediated iron-uptake systems among S. aureus, S. epidermidis, and S. saprophyticus. S. aureus was more susceptible to streptonigrin than the other two staphylococci. S. aureus was able to utilize efficiently transferrin-bound iron in proportion to the level of iron-saturation and produced siderophores in an inverse relation to iron-saturation. In contrast to S. aureus, S. epidermidis and S. saprophyticus were able to utilize only holotransferrin (HT; about 80% iron- saturated) and produced siderophores only in media containing HT. Moreover, they utilized HT less efficiently than S. aureus, though they produced greater amount of siderophores than S. aureus in media containing HT. The ability of the equivalent siderophores per se to capture iron from HT was not significantly different among the three species. Nevertheless, the siderophores from S. aureus stimulated the growth of the staphylococci to a greater degree than did the siderophores from S. epidermidis and S. saprophyticus. The siderophores from S. epidermidis and S. saprophyticus also stimulated the growth of S. aureus to a greater degree than those of the original bacteria which produced them. This indicates that S. aureus possesses a greater ability to produce more-efficient siderophores responding to very low iron-availability, as well as a greater ability to utilize iron-siderophore complexes, than the other two staphylococci. This explains in part the higher virulence of S. aureus compared to other staphylococci.

Bacterial Growth in Amniotic Fluid Is Dependent on the Iron-Availability and the Activity of Bacterial Iron-Uptake System

In the present study, the relationship among iron-availability, antibacterial activity, role of meconium as an iron source and the activity of bacterial iron-uptake system (IUS) for bacterial growth in amniotic fluid (AF) were investigated. Staphylococcus aureus ATCC 6538 and its streptonigrin-resistant (SR) mutant with defective IUS were used as the test strains. The growth of S. aureus in AF was stimulated dosedependently by addition of meconium. Bacterial growth stimulated by meconium was re-inhibited dose-dependently by addition of iron-chelator, dipyridyl and apotransferrin. Iron concentration was correlated with the meconium content in AF (r(2)= 0.989, p=0.001). High-affinity IUS of S. aureus was expressed only in AF but not in AF with meconium. The growth of SR strain was more retarded than that of the parental strain in the iron-deficient brain heart infusion (ID-BHI), clear AF and AF containing apotransferrin. The retarded growth of both strains in the ID-BHI and AF was recovered by addition of holotransferrin, hemoglobin and FeCl3. Taken together, the antibacterial activity of AF is closely related with low iron-availability. Bacterial growth in AF considerably depends on the activity of bacterial IUS. Meconium acts as one of the exogenous iron-sources and thus can stimulate bacterial growth in AF.

Transferrin Binding Protein of Staphylococcus aureus is not Essential for Iron-uptake from Transferrin in vitro

BACKGROUND: Staphylococcus aureus produces siderophore and expresses transferring-binding protein for uptake of iron essentially required for multiplication under the iron-restricted conditions. We investigated which of the two iron-uptake systems is dominant or essential for S. aureus growth. METHODS: Streptonigrin-resistant mutant (SR-1) of S. aureus, isolated by repeated exposure to streptonigrin, was used in this study. SR-1 strain produced less amount of siderophore than the parent strain and did not express the transferring-binding protein. Growth and iron consumption of the two bacteria were compared during cultivation in the media containing various concentrations of iron, by measuring optical densities of the culture fluids at 600 nm and residual iron concentrations of the culture supernatants. RESULTS: Growth of the two bacteria in the iron-sufficient media containing various sources of iron was more active than in the iron-deficient media, in which iron concentration was 0.2 microgram/dL. Growth of SR-1 strain was markedly inhibited in the iron-deficient media with/without apotransferrin (0.5 mg/mL). However, growth of SR-1 strain did not show any difference in the iron-sufficient media containing FeCl3 (0.2 micrometer) and hemoglobin (0.5 mg/mL) as compared with that of the parental strain. Moreover, growth of the two bacteria did not show any difference in the media containing holotransferrin (0.5 mg/mL). There was no difference in iron consumption between the parental and mutant strains, evidenced by the residual iron concentration of the culture supernatants. CONCLUSION: Siderophore production is thought to be dominant or essential iron-uptake system for in vitro growth of S. aureus. The pathogenetic role of multifunctional transferring-binding protein, including transferring-binding activity and glycolytic enzyme activity, is expected to be established through further continued studies.

Transferrin Binding Protein of Staphylococcus aureus is not Essential for Iron-uptake from Transferrin in vitro

BACKGROUND: Staphylococcus aureus produces siderophore and expresses transferring-binding protein for uptake of iron essentially required for multiplication under the iron-restricted conditions. We investigated which of the two iron-uptake systems is dominant or essential for S. aureus growth. METHODS: Streptonigrin-resistant mutant (SR-1) of S. aureus, isolated by repeated exposure to streptonigrin, was used in this study. SR-1 strain produced less amount of siderophore than the parent strain and did not express the transferring-binding protein. Growth and iron consumption of the two bacteria were compared during cultivation in the media containing various concentrations of iron, by measuring optical densities of the culture fluids at 600 nm and residual iron concentrations of the culture supernatants. RESULTS: Growth of the two bacteria in the iron-sufficient media containing various sources of iron was more active than in the iron-deficient media, in which iron concentration was 0.2 microgram/dL. Growth of SR-1 strain was markedly inhibited in the iron-deficient media with/without apotransferrin (0.5 mg/mL). However, growth of SR-1 strain did not show any difference in the iron-sufficient media containing FeCl3 (0.2 micrometer) and hemoglobin (0.5 mg/mL) as compared with that of the parental strain. Moreover, growth of the two bacteria did not show any difference in the media containing holotransferrin (0.5 mg/mL). There was no difference in iron consumption between the parental and mutant strains, evidenced by the residual iron concentration of the culture supernatants. CONCLUSION: Siderophore production is thought to be dominant or essential iron-uptake system for in vitro growth of S. aureus. The pathogenetic role of multifunctional transferring-binding protein, including transferring-binding activity and glycolytic enzyme activity, is expected to be established through further continued studies.

Cell Wall Proteins of Staphylococcus aureus Responsive to Oxygen Tension and Iron Concentration / 감염

BACKGROUND: We previously reported that activity of iron-uptake systems (IUS) influenced on the growth of Staphylococcus aureus in laboratory medium and body fluids according to the iron and oxygen concentrations, which they are closely related each other in several microbial metabolism. In the present study, we tried to investigate the profiles of cell wall proteins of S. aureus according to the change of iron and oxygen concentrations. METHODS: SR-1 strain, whose IUS are defective, was isolated from the standard strain ATCC 6538 by repeated exposure against streptonigrin. These two strains were cultured under the aerobic, microaerobic and anaerobic conditions in the iron-sufficient BHI and iron-depleted BHI, respectively. Cell wall proteins were visualized by Coomassie staining after SDS-PAGE. RESULTS: Cell wall proteins of the both strains were expressed more than under the aerobic condition than under the anaerobic condition in the iron-sufficient medium as well as in the iron-deficient medium. However, expression of cell wall proteins of SR-1 strain was markedly inhibited compared to that of parental ATCC 6538 strain, especially in the iron-deficient medium. Among the proteins more expressed under the aerobic culture condition in the iron-deficient medium, about 88, 55, 39, 36, 35 and 33 kDa of proteins were iron-repressible and oxygen-inducible, and corresponded to the iron-repressible proteins which other researchers reported. CONCLUSION: Expression of cell wall proteins of S. aureus was affected by simultaneous and respective change of iron and oxygen concentrations. Activity of IUS influenced more on the expression of cell wall proteins of S. aureus in the iron-deficient environment than in the iron-sufficient environment. These results suggest the possibility that the iron-repressible and oxygen-inducible proteins mimic those (antigens) found commonly in clinical infections.

Effect of Iron - Uptake Mechanisms of Staphylococcus Aureus on the Growth in Human Body Fluids / 감염

BACKGROUND: We could establish a streptonigrin-resistant strain called SR-1 strain from Staphylococcus aureus ATCC 6538 as a parental strain and characterize SR-1 strain as defective in the iron-uptake mechanisms including production of siderophores and expression of transferrin-binding protein on the cell wall. We performed this study to elucidate effect of the iron-uptake mechanisms on the growth in human body fluids. METHODS: Growth kinetics of SR-1 strain were compared with those of the parental strain and the increase of unsaturated iron-binding capacity (UIBC) was measured. Siderophore production and expression of transferrin-binding protein were detected by CAS diffusion assay and ligand-blot method probed with human transferrin conjugated horseradish peroxidase, respectively, as the strains were cultivated in normal pooled sera, ascitic fluid and pleural effusion. RESULTS: Siderophores activity in the body fluids could not be detected by the CAS diffusion assay. The parental strain expressed the transferrin-binding protein on the cell wall during the growth in ascites and pleural effusion except the sera whereas SR-1 strain did not. Growth kinetics showed that SR-1 strain grew sluggish compared to the parental strain. The peak of increase of UIBC of the parental strain was observed at the mid-exponential growth phase and the increase of UIBC of SR-1 strain was either lower than that of the parental strain or not changed. CONCLUSION: The iron-uptake mechanisms of S. aureus, especially expression of transferrin-binding protein, play a significant role in growing in the body fluids.

Patterns of Iron Utilization According to the Growth of Staphylococcus aureus

To elucidate iron utilization patterns of Staphylococcus aureus according to the growth, we checked the residual iron concentration and the production of siderophores at the indicated times while culturing S. aureus ATCC 6538 and 25923 strains in brain heart infusion broth. By using streptonigrin susceptibility test and investigating growth curves in three culture media of which iron concentration is 0.2, 20, 45 uM, respectively, we found out that iron metabolism of 6538 strain was more active than that of 25923 strain. In point of tendency of iron consumption, 6538 strain steeply consumed iron just before the onset of stationary phase, but 25923 strain did gradually iron throughout the growth phase. Nevertheless, total amount of iron consumed by each strain during the growth was almost no difference between the strains. CAS diffusion assay in detecting siderophores showed that siderophore production followed iron consumption. These results suggest that the siderophores play significant role in iron utilization in vitro.