The following variables will be followed: time and location of positive cultures, underlying diseases and severity of illness, recent immunomodulative therapies, physical exam findings, laboratory and radiographical data, antimicrobial usage within 14 days of onset of bacteremia, microbiological data and resistance patterns, choice of antibiotics once organism identified, suspected source of bacteremia, bacteriological outcomes, laboratory results, demographic information, medications, clinical outcome,gender, height, weight, ethnicity, and past medical history (please see attached clinical data collection worksheet dated 4/2005). We will also collect information retrospectively for one year and prospectively for one year. The bacteria in the patient's blood cultures will be subcultured (after the diagnosis has been obtained since the microbiology lab would otherwise destroy the culture) and provided to the honest broker who will deidentify the specimen and link it to the medical information collected (which will also be deidentified by the honest broker). The following evaluation will be performed on these samples. The minimal inhibitory concentration of the antibiotic used in treatment will be performed by the E-Test method (AB Biodisk, Solna, Sweden). Specific mechanisms of antimicrobial resistance will be studied with emphasis on the presence of beta-lactamases produced by the bacteria. This evaluation will be performed by analytical isoelectric focusing techniques as well as PCR and gene sequencing analysis to determine genes encoding beta-lactamases. Biologic samples will be under the control of the principal investigator of this research project. All samples provided to the investigators are deidentified by the honest broker and will be coded with numbers. The information linking these code numbers to the corresponding subjects' identities will be kept in a separate, secure location that only the honest broker has access to. The investigators on this study will keep the samples indefinitely. Samples will be kept in the investigator's laboratory located in Scaife Hall, room 812, 3500 Terrace Street. At no time with the research investigators have access to any patient identifiers.