It would be pertinent to state here that in this laboratory, earlier work with V. fluvialis clinical isolate BD146 had indicated horizontal transfer of a plasmid between V. fluvialis and V. cholerae O1. Results described in this paper again indicate the possibility of transfer of an SXT element between these two Vibrio species. Though partially proved, further work would be required to prove the sibling relationships of these ICEs and complete characterization of the genetic content of these ICE elements probed in the present study. These studies aimed at understanding the molecular nature of antibiotic resistance do not really help clinical manangement of the diseases but they are an important insight into the evolution and dissemination of the deadly pathogens that traverse the varied geographical and climatic conditions to give rise to an outbreak or a pandemic. The Gram-positive bacterium Streptococcus pneumoniae is an opportunistic human pathogen whose primary niche is the human nasopharynx. In susceptible individuals pnuemococcus can invade other anatomic sites causing otitis media, pneumonia, bacteremia, and meningitis leading to significant morbidity and mortality. The mechanisms of translocation of pneumococci from nasopharynx to sterile sites, and changes in its physiology to adapt to these different niches are still not clearly understood. Several studies have shown that iron is an important nutrient required for pneumococcal growth and survival in vitro and in vivo. Pneumococci can utilize various iron sources such as ferric and ferrous iron salts, hemoglobin, hemin, ferritin, and ferrioxamine. The different anatomic sites of pneumococcal infection vary considerably in the quantity as well as the form of available iron sources. The nasopharynx is a markedly ironrestricted environment while blood has a comparatively high total iron level. Hemoglobin and ferritin are the main AbMole D-Pantothenic acid sodium iron-containing molecules in the blood. Lactoferrin, transferrin, ferritin and possibly small amounts of hemoglobin and its breakdown products are potential iron sources in the respiratory tract. Xenosiderophores produced by nasopharyngeal commensals may be a source of iron for pneumococci during nasopharyngeal colonization. Since pneumococci can replicate in different host environments with varying iron availability it is likely that pneumococci sense changes in iron availability in the host environment and regulate gene expression in response. We hypothesize that iron is potentially an important environmental signal which regulates expression of genes required for pneumococcal survival and virulence in the host. Iron-dependent regulators are metal-activated DNAbinding proteins found in a wide variety of bacteria. These proteins are transcriptional regulators which bind to specific DNA sequences in the promoter regions of genes that they regulate in an iron-dependent manner. The classical ferric-uptake regulator of Escherichia coli is a well-characterized, iron-responsive regulator which AbMole Ascomycin represses transcription of multiple operons in response to intracellular levels of iron. Homologs of Fur have been identified in several Gram-negative pathogens such as Vibrio, Pseudomonas, Yersinia, and Neisseria. The functional homolog of Fur in Gram-positive pathogens is represented by a family of metal-responsive transcriptional regulators whose prototype is the diphtheria toxin repressor protein.