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Biomedical subjects

J N Baldwin

Publications and source records attributed to J N Baldwin.

At least 19 recordsLinked to original sources
PubMed1985

Relatedness of tetracycline resistance plasmids among species of coagulase-negative staphylococci.

Four isolates of Staphylococcus aureus and 98 isolates of coagulase-negative staphylococci representing six species all obtained from endocervical cultures were examined for antimicrobial susceptibility and for the presence of plasmids. More than 80% of the isolates were susceptible to each of 12 antimicrobial agents tested, whereas only 33% were susceptible to penicillin G, 30% were susceptible to cadmium chloride, and 41% were susceptible to tetracycline. Although no species-related susceptibility or plasmid patterns were detected, 77 isolates contained at least one plasmid and 43 contained a plasmid similar in mass to a 2.7-megadalton tetracycline resistance plasmid previously reported in staphylococci. Association of tetracycline resistance with plasmids of this size in four species was determined from curing experiments. No plasmids homologous with the tetracycline resistance locus of the Escherichia coli plasmid pBR322 were found among 11 isolates examined by DNA hybridization. Homology with a 2.7-megadalton plasmids (pRC701) from an endocervical isolate of S. aureus, however, was apparent for 2.7-megadalton plasmids harbored by six isolates as well as with larger plasmids harbored by three isolates. Restriction analysis revealed that pRC701 shared structural identity with two plasmids of a similar mass from two species of coagulase-negative staphylococci as well as with a previously characterized tetracycline resistance plasmid originating in S. aureus.

Base Sequence↗
PubMed1985

Evaluation of a sustained-release theophylline tablet in young asthmatics.

A sustained-release theophylline (SRT) tablet was evaluated in 15 children with moderately severe asthma between the ages of 3 and 5 years (4.2 +/- 0.83 years). They received a mean daily dose of 20.4 mg/kg given q12h for 3 or more weeks with daily symptom scores and twice daily peak flow rates (PFR) measured. Serum theophylline levels (STL) were then obtained at 0, 1, 2, 4, 6, 8, 10, and 12 hr (eight children had 24-hr samples obtained), along with PFRs every 3 hr. The mean peak STL (x +/- SD) was 16.6 +/- 4.4 and the trough was 5.9 +/- 2.8, with a peak-trough difference of 10.6 +/- 3.9. The average time to peak level was 3.9 hr. The mean +/- SD clearance was 1.42 +/- 0.63 ml/kg per min and the apparent T1/2 was 5.11 +/- 1.34 hr. The average weekly morning PFR for the 3-week period ranged from 116.8 +/- 41.2 to 127.4 +/- 37.4 L/min, and the evening PFT ranged from 126.5 +/- 38.4 to 137.0 +/- 40.9 L/min. In conclusion, the SRT tablet is effective in treating many young asthmatics on a 12-hr dosage schedule. For some children who experience excessive peak-trough differences, an 8-hr dosage schedule may be indicated.

Asthma↗
PubMed1984

Percutaneous absorption of iodochlorhydroxyquin in humans.

Iodochlorhydroxyquin (I) is used in the treatment of diaper rash and other skin disorders, and is presumed to undergo little or no percutaneous absorption. The absorption of (I) from a 3% cream was studied in 5 normal male subjects after a single application of the cream for 12 h. Plasma levels of the drug were followed for 24 h after initial application while urinary excretion was measured for 54 h. (I) was extracted from plasma and urine and assayed by high-performance liquid chromatography. The drug in the range of 0.37-0.56 micrograms/ml was detected in plasma 2 h after application and persisted throughout the treatment period. The mean excretion rate after 12 h of application was 58.4 micrograms/h and the excretion rate was 8.8 micrograms/h at 42 h posttreatment. The elimination rate constant was calculated to be 0.15 h-1. Approximately 40% of the drug was absorbed over the 12-h application period. From the above results it is apparent that significant percutaneous absorption of (I) occurs.

Absorption↗
PubMed1981

Isolating specific auxotrophic mutants of Mycobacterium smegmatis by using vancomycin.

After inducing mutagenesis with nitrosoguanidine, we used vancomycin enrichment in isolating auxotrophic mutants of Mycobacterium smegmatis. Compared with cycloserine and penicillin G, which are also cell wall inhibitors, vancomycin, with 24 h of exposure, produced less cell lysis and a greater reduction in viable cell numbers. With vancomycin enrichment, 13 specific auxotrophs were isolated after nitrosoguanidine-induced mutation, whereas only two mutants were isolated without enrichment.

Cell Wall↗
PubMed1981

Penicillin and tetracycline resistance plasmids in Staphylococcus epidermidis.

The genetic nature of penicillin (Pc) and tetracycline (Tc) resistance plasmids in Staphylococcus epidermidis were studied and compared with those in S. aureus. Of 10 S. epidermidis strains transduced for penicillin resistance, we could isolate Pc plasmids from only 3. One of these plasmids also encoded for cadmium resistance and another encoded for resistance to ethidium bromide, traits also associated with S. aureus Pc plasmids. Endonuclease fingerprinting of the Pc plasmids from the two species revealed extensive heterogeneity. Two S. epidermidis strains were also transduced for tetracycline resistance. Both harbored plasmids indistinguishable from S. aureus Tc plasmids as judged by endonuclease fingerprinting. These data suggest that genetic exchange between S. aureus and S. epidermidis occurs in vivo.

Culture Media↗
PubMed1981

Nitrosoguanidine sequential mutagenesis mapping of Mycobacterium tuberculosis genes.

Nitrosoguanidine-induced mutations occur at higher frequencies at the replication region than at other nonreplicating regions of the chromosome. Cultures of Mycobacterium tuberculosis synchronized with phenylethanol were used to determine the order of replication for 10 genes controlling drug resistance. Use of M. tuberculosis provided a 10-h replication map with good resolution because of the slow rate of deoxyribonucleic acid replication. The direction of chromosome replication could not be determined, but this study indicated no pause between rounds of deoxyribonucleic acid replication in a rich medium.

Antibiotics, Antitubercular↗
PubMed1979

Transduction of penicillinase production in Staphylococcus epidermidis and nature of the genetic determinant.

Four strains of Staphylococcus epidermidis from clinical sources were capable of serving as donors for the transduction of either penicillinase production, ethidium bromide resistance, or tetracycline resistance. Three typing phages served as transducing phages and, depending upon the combination of transducing phage, donor strain, and recipient strain, the rates of transduction ranged between 10(-5) and 10(-9). In one strain, cotransduction of penicillinase production and ethidium bromide resistance was observed. Although ultraviolet irradiation kinetics indicated that both the tetracycline resistance and the penicillin resistance determinants were located on plasmids, only resistance to tetracycline could be eliminated by growth in the presence of curing agents or at elevated temperature. However, evidence was obtained by agarose gel electrophoretic studies that both the tetracycline resistance and the penicillin resistance determinants are located on separate plasmids in this organism.

Drug Resistance, Microbial↗
PubMed1979

Stability of penicillin V potassium in unit dose oral syringes.

The stability of reconstituted penicillin V potassium (PVK) when stored in 6-ml plastic oral syringes at various temperatures and protected from light was studied. One batch of PVK was reconstituted with distilled water according to manufacturer's directions (label claim: 125 mg/ml). Samples of 5 ml were stored in plastic oral syringes at 4 C, 25 C, 41 C, 60 C or 75 C and assayed spectrophotometrically and microbiogically at various times. From an initial concentration of 113% of label claim, PVK stored at 4 C (refrigerated) reached 90% of manufacturer's label claim in 11.5 days (95% confidence level). PVK stored at 25 C (room temperature) was unstable after storage for less than 37 hours. PVK degradation followed a first-order process. No significant difference was found between the spectrophotometric and microbiological assay (p less than 0.05). Manufacturer's stability data for storage of reconstituted PVK in the original bulk container should not be applied to PVK repackaged in plastic oral syringes. The pharmacy department developed guideliness designed to prevent the administration of subpotent PVK.

Drug Stability↗
PubMed1978

Rapid procedure for the detection of plasmids in Staphylococcus epidermidis.

A rapid, reproducible, mini-volume assay capable of detecting staphylococcal plasmid DNA in the range of 0.8 to 32 megadaltons has been developed. The assay employs lysostaphin-mediated lysis of cells followed by a short, low-speed centrifugation and does not require treatment with ribonuclease or protease or deproteinization with phenol. A period of only 24 h may be required to detect the presence and size of a plasmid once an organism has been isolated. This method has been used to study the plasmid ecology of Staphylococcus epidermidis and to correlate the presence or absence of plasmids with tetracycline, chloramphenicol, neomycin, penicillin, and cadmium resistances.

Anti-Bacterial Agents↗
PubMed1978

Chromosomal map location of the methicillin resistance determinant in Staphylococcus aureus.

Three-factor genetic crosses performed by transformation have shown that the methicillin resistance determinant of Staphylococcus aureus strain DU4916 (the mec-4916 marker) is linked to a novobiocin resistance (Novr) marker (nov-142) and mutational sites affecting pyrimidine (pyr-141), purine (pur-102), and histidine (hisG15) biosynthesis in S. aureus strain 8325. The linkage group thus defined is pyr-141-hisG15-nov-142-pur-102-mec-4916. Phage 80alpha previously propagated on a novobiocin-resistant, methicillin-sensitive (Mecs) 8325 strain was used to infect 21 novobiocin-sensitive, methicillin-resistant clinical isolates (including strain DU4916). Among the novobiocin-resistant transductants so obtained from each recipient, between 1 and 5% were methicillin sensitive (reflecting cotransduction of Novr and Mecs). These results are consistent with the genetic determinant of methicillin resistance having a single chromosomal locus in most, if not all, strains of S. aureus.

Chromosome Mapping↗
PubMed1978

Self-instructional program on pediatric parenteral nutrition.

A self-instructional package on pediatric parenteral nutrition was designed and its effectiveness in educating health-care practitioners was studied. Participants included eight medical students, 10 pediatricians, 10 pharmacists and 10 pharmacy students at a teaching hospital. Each participant reviewed the program and completed 25-point pre- and posttests. Participants consistently scored higher on the posttest than on the pretest. Further, participants felt that they better understood parenteral nutrition therapy and that they better understood how to write or check orders as a result of their participation in the program. It is suggested that a self-instructional package is an effective method of educating practitioners and students in total parenteral nutrition.

Health Occupations↗
PubMed1977

Nature of the genetic determinant controlling encapsulation in Staphylococcus aureus Smith.

Two strains of Staphylococcus aureus, Smith and M, were studied for the elimination of encapsulation. For S. aureus M, encapsulation was stable. For S. aureus Smith, spontaneous loss of encapsulation was 1.3% and increased markedly in medium containing surface-active agents. In the presence of sodium dodecyl sulfate, unencapsulated cells had a considerable selective advantage. Attempts to demonstrate covalently closed circular plasmid deoxyribonucleic acid were unsuccessful. In cultures of unencapsulated cells, encapsulated cells were observed occasionally. These data argue against a plasmid location for the determinants controlling encapsulation in this organism in spite of a high spontaneous loss of this character.

Chromosomes, Bacterial↗
PubMed1976

Location of the coagulase gene in Staphylococcus aureus.

Evidence is presented for the chromosomal location of the coagulase determinant in most strains of Staphylococcus aureus. By the use of a pour-plate technique, transduction of the capacity to produce coagulase to a coagulase-negative mutant of S. aureus was studied. The frequencies of transduction were low unless the transducing phage was exposed to ultraviolet irradiation and the recipient was lysogenised with the transducing phage. Attempts to transfer the coagulase gene from S. aureus to S. epidermidis were not successful.

Coagulase↗
PubMed1974

Comparison of purified alpha-toxins from various strains of Staphylococcus aureus.

Alpha-toxin from five strains of Staphylococcus aureus, including Wood 46, was purified by isoelectric focusing. The alpha-toxins obtained from different strains were similar. The isoelectric point of the purified toxins was 8.65 +/- 0.15. Sharp concentration peaks were not always obtained. In the ultracentrifuge the alpha-toxins migrated usually as three peaks which could be dissociated with propionic acid to yield one peak. A single line of identity was obtained in immunoelectrophoresis when a heterologous antiserum was reacted with the five purified toxins. It was concluded that the widespread use of the Wood 46 strain for the production of alpha-toxin is justified.

Animals↗