To assess the potential for emergence of resistance during the use of linezolid, we tested 10 clinical isolates of vancomycin-resistant enterococci (VRE) (four Enterococcus faecalis, five Enterococcus faecium, and one Enterococcus gallinarum) as well as a vancomycin-susceptible control (ATCC 29212) strain of E. faecalis. The enterococci were exposed to doubling dilutions of linezolid for 12 passes. After the final passage, the linezolid plate growing VRE contained a higher drug concentration with E. faecalis than with E. faecium. DNA sequencing of the 23S rRNA genes revealed that linezolid resistance in three E. faecalis isolates was associated with a guanine to uracil transversion at bp 2576, while the one E. faecium isolate for which the MIC was 16 g/ml contained a guanine to adenine transition at bp 2505.

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The emergence of resistance in gram-positive bacteria has necessitated a search for new antimicrobial agents. Linezolid is an oxazolidinone, a new class of antibacterial agents with enhanced activity against pathogens. We compared the activity of linezolid to those of other antimicrobial agents against 3,945 clinical isolates. Linezolid demonstrated potent activity against all isolates tested. For all vancomycin-susceptible enterococci, staphylococci, and streptococci, the activity of linezolid was comparable to that of vancomycin. Against oxacillin-resistant staphylococci and vancomycin-resistant enterococci, linezolid was the most active agent tested. In summary, linezolid appears to be a promising new antimicrobial agent for the treatment of gram-positive infections.

Toxin A has historically been regarded as the primary virulence determinant in Clostridium difficile infection, but naturally occurring toxin A-negative, toxin B-positive (A-/B+) C. difficile strains are known to be virulent. To determine the role of toxin B in these strains, we immunized hamsters with a toxoid prepared from purified toxin B to determine whether they would be protected from lethal challenge with an A-/B+ strain of C. difficile.

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Assembly of the heterotrimeric procollagen I molecule is initiated by interactions between the carboxyl propeptide domains of the completed nascent pro alpha chains. The [pro alpha 1(I)]2[pro alpha 2(I)] heterotrimer is the predominant molecule, with much smaller amounts of stable [pro alpha 1(I)]3 homotrimer also being formed. However, the [pro alpha 2(1)]3 homotrimer has not been detected, raising questions as to the mechanism of chain assembly and why [pro alpha2(1)]3 homotrimers are not formed. These questions have been examined here by expressing the intact and amino- or carboxyl-terminal truncated C-propeptides of the pro alpha chains recombinantly in bacteria and in a coupled transcription/translation reticulocyte lysate system. Their interactions were studied in vitro by binding analyses and in vivo by using the yeast two-hybrid system. The C-pro alpha 1(I) interacted with itself, and with C-pro alpha 2(I), as expected. Surprisingly, the C-pro alpha 2(I) also interacted with itself, both in vitro and in vivo. While the interaction of C-pro alpha 2(I) with itself and C-pro alpha 1(I) in vitro was strong, these interactions were weaker in vivo. Deletion of 36 amino acids from the C-terminal domain of C-pro alpha 1 had no effect on its binding to intact self or intact C-pro alpha 2, but the same deletion in C-pro alpha 2 completely abolished its binding to intact C-pro alpha 2 and to C-pro alpha 1. Comparable N-terminal deletions in C-pro alpha 1 or C-pro alpha 2 diminished, but did not abolish, their binding to intact C-pro alpha 1 and C-pro alpha 2. In the yeast two-hybrid system, C-pro alpha 2 interacted with itself more weakly than with C-pro alpha 1. Molecular modeling and circular dichroism analyses showed that C-pro alpha 1 and C-pro alpha 2 have different folded structures and stability. Studies with antibodies specific to the C-pro alpha1 and alpha2 peptides showed them to precipitate different, specific, and distinct cell proteins from fibroblast lysates. The C-pro alpha 2(I) antibody complexed with more cell proteins. We hypothesize that the lack of pro alpha 2(I) homotrimers is not due to the inability of the C-pro alpha 2(I) to interact with itself, but rather to the competing presence of other cell proteins. The specificity of these interactions may reside in conformational differences in N- and C-terminal sequences of the two propeptides or in their different folding patterns.

We investigated the role of polyamines and their regulatory enzyme ornithine decarboxylase in N-methyl-D-aspartate-induced excitotoxicity in embryonic chick retina. N-Methyl-D-aspartate (200 microM) produced an early increase in ornithine decarboxylase activity, putrescine concentration, and Ca2+ entry, leading to selective neuronal death by 30 min. This response was attenuated by the ornithine decarboxylase inhibitor alpha-difluoromethylornithine and the N-methyl-D-aspartate receptor antagonist 5-aminophosphonovaleric acid. Exogenous putrescine increased intracellular putrescine and spermine levels and reversed neuroprotection by alpha-difluoromethylornithine, but not by 5-aminophosphonovaleric acid. N-Methyl-D-aspartate-receptor stimulation of putrescine/polyamine synthesis mediates abnormal Ca2+ entry and acute excitotoxic neuronal death. Postreceptor inhibition of the ornithine decarboxylase/polyamine cascade by alpha-difluoromethylornithine may provide neuroprotection against N-methyl-D-aspartate-induced excitotoxicity.