Optimizing scanning phases in detecting small (<2 cm) hepatocellular carcinoma: whole-liver dynamic study with multidetector row CT.

OBJECTIVE: To define the optimal scanning phases for detecting small hepatocellular carcinomas (HCCs) with whole-liver dynamic helical computed tomography. METHODS: Sixty-one patients with 112 hypervascular HCCs smaller than 2 cm underwent 7-phase dynamic study from the early arterial to the late equilibrium phases of the entire liver. Proof of neoplasms was based on biopsy results and computed tomography with iodized oil. Time-density curves of the individual tumor and the liver were compared. RESULTS: Of 112 hypervascular nodules, the late arterial phase had the best liver-tumor conspicuity (P < 0.001). Ninety-one nodules (81%) had peak liver-tumor contrast in late arterial phase, and only 21 (19%) in the early arterial phase. All the hypervascular HCCs became isoattenuating to the regional parenchyma before the late portal venous phase (120th second). CONCLUSION: The late arterial and late portal venous phases are recommended for detecting small HCC smaller than 2 cm.

PilR enhances the sensitivity of Xanthomonas axonopodis pv. citri to the infection of filamentous bacteriophage Cf.

The pilA gene, which encodes the major structure of pili, is required for infection of Xanthomonas axonopodis pv. citri ( X. a. pv. citri) by the filamentous bacteriophage Cf. Two open reading frames (ORFs) located downstream of pilA were cloned and characterized. One 1392-bp ORF encodes a protein of 464 amino acids which shares substantial similarity with pilR of other bacterial species; the second ORF ( orf618), of 1854-bp, shares sequence similarity with pilS. The existence of the pilR-like and pilS-like genes in various X. campestris pathovars indicated that these two genes are well conserved in Xanthomonas. pilR and pilS mutants were constructed by gene replacement. We found that a pilR mutant, resistant to the infection of phage Cf, was unable to synthesize PilA protein; however, the abundance of the PilA protein and of the pilA transcript was markedly increased by the introduction of a plasmid containing the cloned pilR gene. The restoration of the normal pilus-specific sensitivity of this transformed clone to Cf indicated that the pilR gene functions as a transcriptional regulator of pilA. The pilS mutant, however, was susceptible to Cf infection, and the level of pilA expression in this mutant was similar to that of wild-type cells. Promoter analysis of luciferase reporter gene constructs containing the 5' untranslated regions of pilR or pilS genes revealed that, although the pilR and pilS are contiguous in X. a. pv. citri, the two genes are expressed independently, and the strong pilR promoter leads to the accumulation of PilR in X. a. pv. citri, which positively regulates the biosynthesis of PilA. These results revealed the enhanced sensitivity of X. a. pv. citri to phage Cf in the presence of PilR and indicated that the filamentous phage Cf utilize bacterial pili as a receptor site for its infection.

Genetic organization of the lexA, recA and recX genes in Xanthomonas campestris.

A gene cluster containing lexA, recA and recX genes was previously identified and characterized in Xanthomonas campestris pathovar citri (X. c. pv. citri). We have now cloned and sequenced the corresponding regions in the Xanthomonas campestris pv. campestris (X. c. pv. campestris) and Xanthomonas oryzae pathovar oryzae (X. o. pv. oryzae) chromosome. Sequence analysis of these gene clusters showed significant homology to the previously reported lexA, recA and recX genes. The genetic linkage and the deduced amino acid sequences of these genes displayed very high identity in different pathovars of X. campestris as well as in X. oryzae. Immunoblot analysis revealed that the over-expressed LexA protein of X. c. pv. citri functioned as a repressor of recA expression in X. c. pv. campestris, indicating that the recombinant X. c. pv. citri LexA protein was functional in a different X. campestris pathovar. The abundance of RecA protein was markedly increased upon exposure of X. c. pv. campestris to mitomycin C, and an upstream region of this gene was shown to confer sensitivity to positive regulation by mitomycin C on a luciferase reporter gene construct. A symmetrical sequence of TTAGTAGTAATACTACTAA present within all three Xanthomonas lexA promoters and a highly conserved sequence of TTAGCCCCATACCGAA present in the three regulatory regions of recA indicate that the SOS box of Xanthomonas strains might differ from that of Escherichia coli.