Comparision Of Bacterial Isolates From Blood With Strains Colonizing Gut In Immunocompromised Patients With Bloodstream Infection

A large number of bacteria colonize in human body, mainly in the eye, nasopharynx, oral cavity, skin, urogenital and gastrointestinal tract. And adaptive commensal relationship between humans and their bacteria has been established, supported by the synergistic interplay of multiple human defense mechanisms. Under normal circumstances, a dynamic balance persists among these colonized bacteria, their host and the environment, when these bacteria hardly cause infections and be called normal flora. However, extensive research showed that once the balance was destroyed, these bacteria could translocate and serve as a potential endogenous pathogen, causing various infections. As the largest reservoir of bacteria, human intestinal tract has been getting increasing attention in the study of endogenous infections.This study aims to analyze the homology between pathogens causing blood stream infections (BSI, such as bacteremia and sepsis) and intestinal flora in immuno-compromised patients to elucidate the role of gut flora in endogenous infections. Bacteria identification and resistance patterns were also performed. Bacteria isolated from blood cultures of immunocompromised patients were selected, among which, Escherichia coli and Klebsiella pneumoniae strains composed a big portion. Then, fecal specimen of these patients were obtained. After screening on selective medium, bacteria of the same species as that from blood was selected. Then antimicrobial tests and pulse field gel electrophoresis (PFGE) were performed sequentially to explore the homology between bacteria pairs from blood and feces of the same patient.From April 2009 to April 2010,31 pairs of bacteria were collected from immunocompromised patients, including 21 pairs of E.coli strains and 7 pairs of Kpneumoniae strains. Antimicrobial tests and PFGE were performed with these 28 pairs. The results showed that 20 (71.43%) of the 28 isolates shared identical resistance patterns (resistance phenotype) and 21 pairs (78.57%) shared similar PFGE types. The study clarified the pathogen spectrum of BSI and their drug-resistance status in our hospital, and can provide certain help in the prevention and treatment of endogenous infection in immunocompromised patients. In addition, it provided theoretical basis for the hypothesis that intestinal flora might serve as the potential pathogens to cause endogenous infections in immunocompromised patients.