High-frequency persistence to the lethal effects of inhibition of either DNA or peptidoglycan synthesis, the Hip phenotype, results from mutations at the hip locus of Escherichia coli K-12 The nucleotide sequence of DNA fragments which complement these mutations revealed an operon consisting of a possible regulatory region, including sequences with modest homology to an E coli promoter, and two open reading frames which are translated both in vitro and in vivo The stop codon of a 264-bp open reading frame, hipB, and the start codon of a 1,320-bp open reading frame, hipA, share an adenine residue Assays of promoter strength, the location of the probable promoter with respect to the start of transcription, and codon usage all indicate that hipB and hipA are weakly expressed genes The activity of the promoter is impaired by an adjacent downstream sequence which includes the coding region of hipB The impairment is partially relieved by insertion of a premature translation termination signal within the coding region of hipB, suggesting involvement of the HipB protein in the regulation of this promoter The arrangement of hipB and hipA within the operon and the toxicity of hipA for strains defective in or lacking hipB suggest an important interaction between the products of these genes

Structure and organization of hip, an operon that affects lethality due to inhibition of peptidoglycan or DNA synthesis.

Thymidine concentrations in serum and urine of different animal species and man.

Footpad infection of guinea pigs with herpes simplex virus led to an acute local inflammatory reaction, followed by a persistent latent infection of lumbosacral dorsal root ganglia. Spontaneous reactivation of the latent virus occurred, leading to recurrent lesions at the site of the initial infection. Clinical observations and virological studies during the acute latent and recurrent infection are reported.

Herpes simplex virus infection in guinea pigs: an animal model for studying latent and recurrent herpes simplex virus infection.

A. Acute Toxicity 204 B. Chronic Toxicity 204 C. Teratogenicity 205 D. Chromosome Studies 205 E. Carcinogenicity 205 F. Immunosuppression 205 G. Glucose-6-Phosphate Dehydrogenase Deficiency 205 H. Folate Deficiency 205

Trimethoprim-Sulfamethoxazole: An Assessment of More Than 12 Years of Use

High-level (greater than 1,000 micrograms/ml) resistance to the antimicrobial agent trimethoprim was found in 17 of 101 (17%) coagulase-negative staphylococci and 5 of 51 (10%) Staphylococcus aureus from a number of different hospitals in the United States. Resistance was plasmid encoded and could be transferred by conjugation in 4 of the 17 (24%) Tpr coagulase-negative staphylococci and 3 of the 5 (60%) Tpr S. aureus. A 1.2-kilobase segment of plasmid DNA from one of the plasmids (pG01) was cloned on a high-copy-number vector in Escherichia coli and expressed high-level Tpr (MIC, 1,025 micrograms/ml) in the gram-negative host. In situ filter hybridization demonstrated homology between the cloned Tpr gene probe and plasmid DNA from each conjugative Tpr plasmid, a single nonconjugative plasmid from a United States Staphylococcus epidermidis isolate, a nonconjugative plasmid from an Australian methicillin-resistant S. aureus isolate, and chromosomal DNA from three Tpr S. epidermidis isolates that did not contain any plasmid DNA that was homologous with the probe. No homology was seen between the probe and staphylococcal plasmids not mediating Tpr, plasmid DNA from 12 Tpr S. epidermidis isolates not transferring Tpr by conjugation, or plasmid-encoded Tpr genes derived from gram-negative bacteria. Plasmid-encoded Tpr appears to be a relatively new gene in staphylococci and, because it can be transferred by conjugation, could become more prevalent in nonsocomial isolates.

Plasmid-encoded trimethoprim resistance in staphylococci.

Rich media support the growth of bacteria in the presence of concentrations of sulfonamides and diaminopyrimidines that are highly inhibitory when the organisms are grown on minimal media Many such rich media can be made more suitable for susceptibility testing by the incorporation of lysed horse blood Harper and Cawston characterized the active substance, Harper-Cawston factor (HCF), and later studies indicated it to be a protein It has now been identified as thymidine phosphorylase The identification follows from the identical purification pattern of HCF and thymidine phosphorylase activities from horse blood to a high degree of purity Blood of goats, sheep, oxen, geese, chickens, cows, dogs, rats, and humans had neither biological activity The identification of HCF as thymidine phosphorylase is consistent with the earlier findings of Koch and Burchall (1971) that most of the interfering effects of rich media could be accounted for by their thymidine contents, and that thymidine is much more active in this respect than is thymine

Identification of Harper-Cawston Factor as Thymidine Phosphorylase and Removal from Media of Substances Interfering with Susceptibility Testing to Sulfonamides and Diaminopyrimidines

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Identification of Harper-Cawston Factor as Thymidine Phosphorylase and Removal from Media of Substances Interfering with Susceptibility Testing to Sulfonamides and Diaminopyrimidines