Natural Transformation of Helicobacter pylori Involves the Integration of Short DNA Fragments Interrupted by Gaps of Variable Size

Helicobacter pylori are gram-negative bacteria notable for their high level of genetic diversity and plasticity, features that may play a key role in the organism's ability to colonize the human stomach. Homeologous natural transformation, a key contributor to genomic diversification, has been well-described for H. pylori. To examine the mechanisms involved, we performed restriction analysis and sequencing of recombination products to characterize the length, fragmentation, and position of DNA imported via natural transformation. Our analysis revealed DNA imports of small size (1,300 bp, 95% confidence limits 950–1850 bp) with instances of substantial asymmetry in relation to selectable antibiotic-resistance markers. We also observed clustering of imported DNA endpoints, suggesting a possible role for restriction endonucleases in limiting recombination length. Additionally, we observed gaps in integrated DNA and found evidence suggesting that these gaps are the result of two or more separate strand invasions. Taken together, these observations support a system of highly efficient short-fragment recombination involving multiple recombination events within a single locus

Severe cytomegalovirus infection in multiply transfused, splenectomized, trauma patients

During a 2-year period 5 previously healthy young men who had undergone splenectomy and received multiple transfusions for trauma had severe cytomegalovirus (CMV) infection. Their illness was characterised by a long period of high fever, severe interstitial pneumonitis with dyspnoea and hypoxaemia, and an unusually high lymphocytosis (12 000-26 000 cells/microliter) with numerous atypical forms. The presumptive diagnosis was based on the patients' seroconversion and viral excretion, on the clinical and haematological findings which were typical of severe CMV infection, and on the absence of other infective organisms. In 1 case widespread CMV pneumonitis was confirmed at necropsy. These observations raise the possibility that splenectomy increases the severity and modifies the pattern of CMV infection, since during the same period no other case of severe CMV infection was observed among a large number of patients who had received multiple transfusions but had not undergone splenectomy