Karuna Gokarn et al., j Biosci Tech, Vol 1 (3),2010,127‐134 127 Siderophores and Pathogenecity of Microorganisms R. B. Pal, Karuna Gokarn Department of Microbiology,Sir Hurkisondas Nurrotumdas Medical Research Society, R.R Road, Mumbai 400 004 E.mail: ram prasad_pal@hnhospital. com E.mail: karuna gokarn@gmail. com Abstract Introduction: The ability of pathogenic microorganisms of obtaining iron from host is essential for its survival. Microorganisms require iron for a variety of metabolic processes, so they synthesize and secrete small organic molecules called siderophores that actively chelate iron. The study was carried out to compare the results of siderophore produced by commensals & clinical isolates and co-relate it to pathogenecity. Materials & Methods: Detection of microbial siderophore production was carried out qualitatively by the chrome azurol sulfonate (CAS) plate assay. Spectrophotometric assay (Liquid CAS assay) was used for quantitative estimation of siderophore produced by the organisms. Qualitative assay for determining type of siderophore was also carried by Arnow’s & Csaky’s methods. Results: The commensals & the isolates from clinical samples did not show any significant difference in the production of siderophore. It was also observed that the optimum condition for siderophore production by both the commensals & the clinical isolates was at 37 0 C for 24 hours with aeration in an iron deficient medium. Conclusion: One cannot use siderophore production as a determinant of virulence of an organism. Thus, it is concluded that siderophore production may be a necessary feature of a bacterium, but not a determinant of virulence. The siderophore producing potential of a pathogen in vivo cannot be decided on basis of in-vitro assays. But applications of siderophores could be many if well studied. Keywords: Catecholate, Chrome azurol sulfonate, hydroxamate, Siderophores 1. Introduction: A Siderophore (Greek for iron carrier) is a low molecular weight (500-1000daltons), high affinity ferric iron-chelating compound secreted by organisms. Is it one of the determinants for virulence of a pathogen. In iron-limited environment, siderophore production is derepressed and excreted extracellularly. The siderophore then acts to sequester and solubilize the iron. The amount of free iron available in the human host is extremely low (10 -18 M), which is insufficient for bacterial growth. The ability of obtaining iron from the host is essential for the survival of microorganisms. Microorganisms require iron for a variety of metabolic processes, so they synthesize and secrete siderophores that actively chelate iron and remove it from eukaryotic iron-binding proteins like lactoferrin & transferring. Thus, iron is a key element of bacterial pathogenesis. [4] Therefore studies were carried out 1. To evaluate the pathogenecity of different clinical isolates 2. To compare the results of siderophore produced by commensals & clinical isolates. 2. Materials and Methods: 2.1. Collection of the cultures: Culture isolates from clinical specimens were collected from the Pathology Department of Sir H. N. Hospital and Research Centre, Mumbai, India of which there were 17 strains E. coli, 6 Acinetobacter spp., 8 Klebsiella spp, 2 Branhamella catarrhalis & 4 Proteus spp. E. coli (11) and Acinetobacter (5) isolates from the stool samples and throat swabs respectively from healthy individuals were also collected to compare the siderophore