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Biomedical subjects

R B Roberts

Publications and source records attributed to R B Roberts.

At least 73 records · Page 4Linked to original sources
PubMed1982

Vitamin B6 requirements of nutritionally variant Streptococcus mitior.

The growth rate of three vitamin B6-dependent Streptococcus mitior (B6DS) and two non-B6DS strains in Todd-Hewitt broth, with and without vitamin B6 supplementation, was examined. Even in optimally supplemented culture media, the growth rate of the three B6DS strains was much slower than that of comparable non-B6DS strains. Uptake studies with [3H] pyridoxine suggest that these B6DS strains cannot assimilate pyridoxine. Although not transported intracellularly, pyridoxine inhibited the growth of B6DS strains in media supplemented with other vitamin B6 analogs, probably by binding to the vitamin B6 transport system and inhibiting the uptake of the other vitamin B6 analogs.

Biological Transport↗
PubMed1981

Neisseria meningitidis serogroup W 135 disease in adults.

Five adults had infection caused by Neisseria meningitidis serogroup W135. Their ages ranged from 19 to 74 years, and the spectrum of illness included meningitis, pneumonia, and acute peritonitis. Two patients had systemic lupus erythematosus and were receiving corticosteroids at the time of their infection. One patient died of fulminant meningococcemia. All isolates were sensitive to sulfonamides. The recent increase in the national incidence of N meningitidis serogroup W135 infections emphasizes the need for continuing surveillance and justifies its inclusion in a polyvalent meningococcal vaccine.

Adult↗
PubMed1981

Toxicity of acephate and methamidophos to dark-eyed juncos.

The calculated, acute oral LD50 of acephate and methamidophos to dark-eyed juncos (Junco hyemalis) was 106 mg/kg and 8 mg/kg, respectively. Brain cholinesterase (ChE) activity in birds that died after acephate poisoning was depressed 80% below that of control birds. Birds that died of acute methamidophos poisoning had brain ChE depression of 60%. The birds killed by acephate had brain acephate residue concentrations greater than 2 mg/kg and methamidophos concentrations usually greater than 0.25 mg/kg. Eighty percent of the birds killed with methamidophos had brain methamidophos concentrations greater than 0.1 mg/kg. The five-day feeding LC50 for acephate was 1485 mg/kg. Brain ChE activities of birds which died early in the study were less depressed (51.5%) than those which died at a later date (69.6%). Brain residues of acephate and methamidophos were lower in these birds than in the birds of the acute oral LD50 studies. Brain ChE activity returned to normal within three days after the birds received a single sublethal dose of acephate. These studies indicate that the amount of acephate needed to produce the ChE depression found in other investigations in most dark-eyed juncos exposed to forest applications of insecticide is about one-fifth of the LD50; however, in a few birds the ChE activity may be depressed to near lethal levels.

Animals↗
PubMed1981

Recovery of adrenal reserve following treatment of disseminated South American blastomycosis.

South American blastomycosis commonly involves the adrenal glands as proved in autopsy series, although clinical adrenocortical insufficiency is infrequently suspected. In 1972, an Ecuadorian man was seen with disseminated paracoccidioidomycosis and Addison's disease documented by low basal steroid levels and lack of response to ACTH therapy. The patient has since been treated with a total dose of 4,000 mg of amphotericin B. He discontinued all steroid replacement therapy for two years but remained asymptomatic. Recent evaluation documented improvement in basal steroid production, particularly mineralocorticoids. Adrenal reserve has also been demonstrated by the response of glucocorticoids to ACTH stimulation. This is the first well documented case in which adrenal reserve was recovered following treatment of granulomatous Addison's disease.

Addison Disease↗
PubMed1981

Evaluation of blood culture media for isolation of pyridoxal-dependent Streptococcus mitior (mitis).

Nutritional variant streptococci identified as pyridoxal-dependent Streptococcus mitior (mitis) account for 5 to 6% of streptococcal endocarditis and may be a cause of "culture-negative" endocarditis. Hence, growth of three variant strains in 11 commercial blood culture broths was compared to that in fresh heart infusion broth. For simulation of clinical specimens, culture bottles were injected with 5 ml of human blood, inoculated with approximately 500 colony-forming units (CFU) per bottle, and monitored for 7 days with Gram stains and viable counts. Only Thiol broth (Difco Laboratories, Detroit, Mich.) supported growth without blood at this low inoculum. In media containing blood, maximal growth of 10(9) CFU/ml was reached within 2 days of incubation, and heavy turbidity was consistently observed in only heart infusion broth, Thiol broth, and media supplemented with pyridoxal hydrochloride. Columbia broth (BBL Microbiology Systems, Cockeysville, Md.) with increased cysteine, thioglycollate broth, and one brain heart infusion broth produced moderate growth (1 x 10(8) to 5 x 10(8) CFU/ml), whereas Columbia broth, another brain heart infusion broth, and two brands of tryptic soy broth showed fair growth (1 x 10(7) to 4 x 10(7) CFU/ml). The poor growth (1 x 10(6) to 3 x 10(6) CFU/ml) observed in three other brands of tryptic soy broth was often not apparent macroscopically or by Gram stain. Furthermore, on growth occurred in 40% of tryptic soy broth cultures inoculated with 50 CFU. Therefore, to ensure isolation of these variant streptococci from clinical blood cultures, a medium containing thiol compounds or supplemented with pyridoxal should be used. Subcultures should be made within 2 days of incubation to blood agar enriched with pyridoxal or containing a Staphylococcus sp. streak for satellitism.

Animals↗
PubMed1980

Gonococci-human polymorphonuclear leukocyte interactions: metabolic studies associated with attachment and ingestion.

Utilizing monolayers of human polymorphonuclear leukocytes, optimal conditions for attachment and ingestion of Neisseria gonorrhoeae were determined. Both attachment and ingestion were optimal at 36 degrees C when a bacteria-leukocyte ratio of 100:1 was employed. After 30 min of incubation, log-phase viable type 2 gonococci were attached to 90% of leukocytes, whereas log-phase viable type 4 gonococci were ingested by 80 to 90% of cells. Respiratory inhibitors had no effect on attachment or ingestion, whereas glycolytic inhibitors blocked ingestion but did not affect attachment of gonocci to the leukocyte surface. Inhibition was dose dependent and partially reversible. The oxidative metabolism of leukocytes with gonococci attached or ingested was also examined. Attachment of log-phase type 2 gonococci stimulated a minimal increase in glucose oxidation and oxygen consumption by leukocytes in contrast to marked increases by leukocytes that had ingested viable type 4 or heat-killed typed 2 organisms. These results demonstrate that attachment of log-phase type 2 gonococci to the surface membrane does not stimulate significant leukocyte oxidative metabolism nor initiate the phagocytic process.

Glucose↗
PubMed1980

Comparative study of diarrhea associated with clindamycin and ampicillin therapy.

The incidence of diarrhea associated with clindamycin and ampicillin was studied prospectively among 606 adult inpatients during a 12-month period. Clindamycin was administered to 288 patients of whom 145 received clindamycin in combination with ampicillin. A comparable group of 318 patients received ampicillin alone. Underlying diseases, diets and medications other than antibiotics studied were implicated in the etiology of diarrhea in 25--40% of patients. The incidence of diarrhea due to ampicillin and clindamycin was 3.8 and 4.2%, respectively (P greater than 0.05). The incidence of diarrhea in patients who received both drugs was 9.0% (P less than 0.05). Diarrhea which developed after completion of antibiotic therapy was two-to-three fold longer in duration than that which occurred during drug administration. This finding underscores the necessity to follow patients closely for at least four to six weeks after receiving such medications.

Adolescent↗
PubMed1979

The role of natural IgG and complement in the phagocytosis of type 4 Neisseria gonorrhoeae by human polymorphonuclear leukocytes.

The role of human serum components in the phagocytosis of logarithmic-phase type 4 Neisseria gonorrhoeae by human polymorphononuclear leukocytes was investigated. The requirement of fresh normal human serum (FHS) for optimal phagocytosis and the fixation of human immunoglobulin (IgG) and complenet (C3) to the gonococcal cell surface suggested that both serum factors participate in the phagocytosis of these organisms. The percentage of neutrophils containing ingested organisms was directly proportional to the concentration of IgG purified from FHS. Absorption studies suggested that this natural IgG binds to a trypsin-sensitive surface protein on type 4 gonococci and cross-reacts with stationary-phase type 2 N. gonorrhoeae, group C Neisseria meningitidis, and Branhamella catarrhalis, but not with logarithmic-phase type 2 gonococci or other Neisseria species. Although complement alone did not promote phagocytosis, it enhanced IgG-mediated ingestion. Studies using C2-deficient serum or serum chelators indicated that the alternative complement pathway participates in this interaction.

Agammaglobulinemia↗
PubMed1978

Contribution of maternal circulation to blood-borne progesterone in the fetus. II. Studies on sheep.

Catheters were placed in maternal and fetal vessels in four ewes in the last month of gestation. Tritiated progesterone (P) was infused at a constant rate into a maternal peripheral vein. Specific activities and endogenous concentrations of P were measured in blood samples drawn from a maternal artery and either a fetal femoral artery or an umbilical vein. Comparison of the specific activities of P in fetal and maternal samples revealed that direct secretion of the placental hormone into the umbilical vein accounted for 90 to 93 per cent of the hormone in the fetal circulation. Estimates of the rates of production of P in the fetal circulation, obtained by multiplying metabolic clearance rates previously reported and concentrations of P in a fetal femoral artery, indicate that placental P is preferentially secreted toward the maternal circulation.

Animals↗
PubMed1978

Serious infections caused by Streptococcus milleri.

Viridans streptococci continue to be the most common etiologic agents in bacterial endocarditis. The spectrum of diseases other than endocarditis caused by these organisms, however, has received sparse attention. Moreover, little clinical information is available concerning the individual viridans streptococcal species. During the 16 months of this study, one species of viridans streptococci, Streptococcus milleri, caused a surprising number of clinically significant suppurative infections. Clinical syndromes included the following: abscesses, 10 cases; peritonitis, four cases; endocarditis, three cases; cholangitis, empyema and cellulitis, one case each. A gastrointestinal source was apparent in eight of these 20 cases. Review of 58 cases of viridans streptococcal endocarditis demonstrated that although Strep. milleri was an infrequent cause of endocarditis, this species was associated with an unusual frequency of suppurative complications. Our experience suggests that Strep. milleri may be more commonly associated with serious suppurative infections than other viridans streptococci and that species identification may be a clinically useful procedure.

Aged↗