Intentional use of carbapenem antibiotics for valproic acid toxicity: A case report.

WHAT IS KNOWN AND OBJECTIVE: The interaction between valproic acid (VPA) and carbapenem antibiotics is well described with previous reports suggesting a reduction in VPA half-life between 47% and 90%. As described in this case, this interaction might be beneficial in the setting of toxic VPA ingestion. CASE DESCRIPTION: An intubated, unresponsive patient arrived via emergency medical services after toxic VPA ingestion. Meropenem was prescribed for a suspected pneumonia and to take advantage of the VPA interaction. We observed a 56% decline in half-life with short-term meropenem dosing and an improvement in mental status shortly after administration. WHAT IS NEW AND CONCLUSION: Our findings suggest a potential role for short-term carbapenem therapy for VPA overdose.

Termination of DNA replication in Escherichia coli requires a trans-acting factor.

The terminus region of the Escherichia coli chromosome contains two sites that inhibit the progression of DNA replication forks. These termination sites, designated T1 and T2, are separated by 7.5 min (350 kilobases [kb]) on the genetic map and are located at the extremities of the terminus region. They demonstrate polarity (they stop replication forks traveling in one direction but not the other) and inhibit replication forks that have passed through and are about to leave the terminus. We have used deletion mutations in the terminus region to map the locations of T1 and T2 more accurately and to initiate studies on the mechanism of replication fork inhibition. We have narrowed the boundaries of T1 and T2 to 20 and 4 kb, respectively. T1 maps between kb 80 and 100 on the physical map of the terminus region (J. P. Bouché, J. Mol. Biol. 154:1-20, 1982), and T2 maps between kb 438 and 442. In addition, we report here that deletion of the region containing the T2 termination site inactivated T1. Supplying the T2 region on a plasmid restored T1 function, demonstrating that inhibition of replication at T1 requires a trans-acting factor which maps in the vicinity of termination site T2. We have called this newly identified terminus function the termination utilization substance (tus).

Transformation of Clostridium perfringens.

Clostridium perfringens 11268 CDR (Rifr Tcs), the strain transformed in our experiments, was generated by curing a spontaneous, rifampicin-resistant mutant of C. perfringens 11268 (Rifr Tcr). High-temperature growth yielded tetracycline-sensitive, rifampicin-resistant cells which no longer contained pCW3, a 42.8-kilobase plasmid. The tetracycline-sensitive, rod-shaped cell was then converted to an L-phase variant by growth in the presence of penicillin G (10 micrograms/ml) and 0.4 M sucrose. After several passages, the antibiotic was removed from the medium, and cells continued to grow as L-phase variants. Another large plasmid, pJU124 (38.8 kilobases), which confers tetracycline resistance, was used for transformation. Transformation of L-phase variants of C. perfringens 11268 CDR (Rifr Tcs) was mediated by polyethylene glycol. Transformation frequency is a nonlinear function of DNA concentration. Restriction analysis showed that the plasmid isolated from the transformants was identical to that supplied. Stable L-phase variants do not revert to rod-shaped cells, but autoplasts can be both transformed and reverted.

Shuttle plasmids for Escherichia coli and Clostridium perfringens.

Small plasmids which replicate in both Escherichia coli and Clostridium perfringens were made by recombining E. coli plasmid pBR322 with three different small (less than 4 kilobases) plasmids native to C. perfringens. Subsequently, two homologous, though distinct, tetracycline resistance determinants (tet) from other C. perfringens plasmids were cloned into them. Both tet systems made E. coli resistant to at least 5 micrograms of tetracycline per ml when resident on the shuttle plasmids. The shuttle vectors have been used to transform L-phase variants and autoplasts of C. perfringens. In the latter case, the intact transforming plasmid could be isolated from walled cells after cell wall regeneration. Reciprocal transformation experiments in which plasmid DNAs derived from E. coli or C. perfringens were used suggest that restriction barriers exist between these two organisms. The plasmids contain restriction enzyme recognition sites in locations which are useful for cloning experiments.