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CSA-13 retained potent antibacterial activity against S. aureus over the course of 30 serial passages. Resistance generated in Gram-negative bacteria correlates with modifications to the outer membranes of these organisms and was not stable outside of the presence of the antimicrobial.

The maximum amount of nickel released from all tested arch wires was 700 times lower than the concentrations necessary to elicit cytotoxic reactions in human PBMCs.

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Escherichia coli O157:H7 carries a chromosomal msbB1 and a plasmid-encoded msbB2 gene. We characterized msbB2 function as a homologue of msbB1 by examination of wild-type organisms and mutant strains that lacked functional msbB1, msbB2, and both msbB1 and msbB2. The msbB double-mutant strain generated pentaacyl lipid A, while the single-mutant strains synthesized hexaacyl lipid A. Complementation with overexpressed msbB2 converted pentaacyl into hexaacyl lipid A in the double-mutant strain. The transcription of both msbB genes occurred simultaneously. Lack of MsbB2 activity slightly increased the microheterogeneity of the lipid A species. These results suggest that the msbB2 gene plays a role not only in the routine generation of fully hexaacylated lipid A but also in suppressing the microheterogeneity of lipid A species, the endotoxic determinant of the organism.Typical enterohemorrhagic Escherichia coli (EHEC) has the ability to produce Shiga toxin (Stx) and to induce attaching and effacing lesions in the intestine. Among the EHEC strains, serotype O157:H7 is the most frequently encountered in disease outbreaks and in severe sequelae worldwide (3, 23, 31). All O157:H7 strains possess an approximately 92-kb plasmid called pO157, which encodes several virulence-associated genes including the following: ehxA, which encodes an RTX type of hemolysin; katP, which encodes a catalase-peroxidase; espP, which encodes a serine protease; and toxB, whose product confers adhesiveness to cultured host cells (20,31). The pO157 plasmid also carries a homologue (msbB2) of the chromosomal msbB (multicopy suppressor of htrB) gene, herein designated msbB1. This fact raises questions about the role of msbB2 in lipid A biosynthesis, cell wall composition, and intestinal colonization by EHEC O157:H7. A recent report showed that chromosomal and plasmid-encoded msbB genes are also present in Shigella flexneri and are required for maximal acylation of lipid A and invasion of the intestinal epithelium (10). The msbB2 gene is part of a locus comprising the consecutive open reading frames (ORFs) shf-rfbU-virK-msbB in the virulence plasmid pWR100 of S. flexneri. This locus is also conserved in pO157 (5, 21, 33) and is hereby designated as the shf locus.The occurrence of the msbB2 gene may imply a role in virulence by modulation of lipid A species that affect the host response to lipopolysaccharide (LPS), but this has not been investigated in E. coli O157:H7. The chromosomal msbB1 gene is 99% identical in nucleotide sequence to the E. coli K-12 msbB gene. The deduced amino acid sequence of the MsbB2 protein is 67% identical to the counterpart MsbB1 protein. The MsbB2 proteins of plasmids pO157 and pWR100 are 69% identical at the amino acid level.The K-12 msbB gene was originally identified as a multicopy suppressor of the null mutant phenotype of the htrB (hightemperature requirement) gene, which encodes a protein that supports growth of the mutant strain in rich media at temperatures above 33°C (17, 18). Later, the enzymatic functions of th...