Genetic locus required for antigenic maturation of Rhizobium etli CE3 lipopolysaccharide.

Rhizobium etli modifies lipopolysaccharide (LPS) structure in response to environmental signals, such as low pH and anthocyanins. These LPS modifications result in the loss of reactivity with certain monoclonal antibodies. The same antibodies fail to recognize previously isolated R. etli mutant strain CE367, even in the absence of such environmental cues. Chemical analysis of the LPS in strain CE367 demonstrated that it lacked the terminal sugar of the wild-type O antigen, 2,3,4-tri-O-methylfucose. A 3-kb stretch of DNA, designated as lpe3, restored wild-type antigenicity when transferred into CE367. From the sequence of this DNA, five open reading frames were postulated. Site-directed mutagenesis and complementation analysis suggested that the genes were organized in at least two transcriptional units, both of which were required for the production of LPS reactive with the diagnostic antibodies. Growth in anthocyanins or at low pH did not alter the specific expression of gusA from the transposon insertion of mutant CE367, nor did the presence of multiple copies of lpe3 situated behind a strong, constitutive promoter prevent epitope changes induced by these environmental cues. Mutations of the lpe genes did not prevent normal nodule development on Phaseolus vulgaris and had very little effect on the occupation of nodules in competition with the wild-type strain.

Pseudoaneurysm: diagnosis with color Doppler ultrasound.

Increasing numbers of interventional radiologic procedures, often with large arterial catheters, have led to increasing total numbers of complications. Pseudoaneurysm is not an infrequent complication. It is often difficult to differentiate pseudoaneurysm clinically from hematoma. In the past, we have used gray scale duplex scanning to aid in this differentiation. We have recently found color Doppler scanning to allow quicker, easier, and more accurate diagnosis. Color Doppler imaging also can often demonstrate the track between the artery and the aneurysm.