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Biomedical subjects

V R Dowell

Publications and source records attributed to V R Dowell.

At least 55 records · Page 3Linked to original sources
PubMed1977

Cultural and physiological characteristics of Clostridium botulinum type G and the susceptibility of certain animals to its toxin.

Strain 89 of Clostridium botulinum type G, isolated by Gimenez and Ciccarelli in 1969, was characterized culturally, biochemically, and toxigenically. It was motile, hemolytic asaccharolytic, weakly proteolytic, lipase and lecithinase negative, and it produced acetic, isobutyric, butyric, and isovaleric acids in peptone-yeast extract-glucose broth. No spores were seen in smears from solid or liquid media. Very low levels of toxin were produced in regular broth cultures, but dialysis cultures yielded 30,000 mouse 50% mean lethal doses (LD50 per kg, orally and subcutaneously, respectively; and for guinea pigs, 10,000 to 20,000 and 100 mouse LD50 per kig, intragastrically and intraperitoneally, respectively.

Animals↗
PubMed1977

Fluorescent-antibody studies on selected strains of Bacteroides fragilis subspecies fragilis.

Antisera against seven strains of Bacteroides fragilis subspecies fragilis were produced from dense suspensions of whole cells. These sera exhibited high agglutination titers with homologous antigens. Reciprocal cross-reactions in agglutination tests with each immunizing strain yielded lower titers. Both the indirect and direct fluorescent-antibody techniques were used to evaluate these reagents in the serological identification of 24 defined strains of B. fragilis subspecies fragilis. Subspecies and even strain specificities were noted with particular antisera. A pooled antiserum and conjugate were prepared and studied. Study results showed that specific and high-titered antisera against strains within this subspecies can be produced by the methods described herein and that possibly more than one serotype exists within the seven strains studied. The development of more antibody pools will be necessary to encompass a wider antigenic coverage before the fluorescent-antibody technique can be relied upon altogether for serologically identifying isolates of B. fragilis subspecies fragilis. Test data showed that the indirect method of fluorescent-antibody staining with whole antiserum is an excellent means of identifying strains of this organism.

Agglutination Tests↗
PubMed1976

Laboratory diagnosis of botulism complicated by pyridostigmine treatment of the patient. A method for selectively removing interfering substances from clinical specimens.

In August 1974, a case of botulism occurred; home-canned potatoes and peas containing Clostridium botulinum, type A, were strongly incriminated as the vehicle of transmission. C. botulinum, type A, was isolated from a stool specimen of the patient, but the mouse neutralization test for botulinal toxin could not be completed because the stool extract contained a highly toxic, heat-stable substance that rapidly killed mice. Historical and laboratory evidence indicated that the substance was pyridostigmine bromide, a low-molecular-weight drug with which the patient had been treated after her disease was misdiagnosed as myasthenia gravis. A generally applicable method employing dialysis by which toxic SUBSTANCED of low molecular weigth could be selectively removed from specimens without diminishing the potency of botulinal toxin contained in them was developed. Dialysis rendered a pyridostigmine solution, a stool extract from the patient with botulism, and a stool extract from a person taking pyridostigmine virtually nontoxic to mice. Dialysis did not significantly alter the toxicity to mice of crude botulinal toxin; it selectively eliminated all or almost all pyridostigmine toxicity from a pyridostigmine-botulinal toxin mixture without altering the toxicity of the botulinal toxin.

Animals↗
PubMed1976

Modification of the Minitek Miniaturized Differentiation System for characterization of anaerobic bacteria.

The Minitek Miniaturized System (BBL) was modified for characterization of anaerobic bacteria. The modified system and the conventional Center for Disease Control method were used to test a variety of anaerobic bacteria, and results were compared. Tests performed by both techniques were indole and H2S production, esculin hydrolysis, nitrate reduction, and fermentation of glucose, mannitol, lactose, sucrose, maltose, salicin, glycerol, xylose, arabinose, mannose, rhamnose, and trehalose. The manufacturer's recommended procedure for the Minitek system was modified by using a new suspension medium (Lombard-Dowell broth) and an inoculum equivalent to the density of a McFarland no. 5 nephelometer standard. The Minitek results, recorded after 48 h, agreed satisfactorily with the conventional test results, usually recorded after 5 to 7 days of incubation. In the examination of 80 strains representing 22 different species or subspecies of anaerobic bacteria, with 16 biochemical tests performed in triplicate, 93.8% of the Minitek test results agreed with those of the corresponding conventional tests. Only tests for indole, H2S, and nitrate reduction gave less than 90% agreement. It was concluded that the modified Minitek system is a suitable substitute for the more expensive and time-consuming conventional procedure for determining carbohydrate fermentation and esculin hydrolysis by anaerobes. This system, when used in conjunction with other tests, can effectively aid in the definitive identification of commonly isolated anaerobes.

Anaerobiosis↗
PubMed1975

A continuing common-source outbreak of botulism in a family.

In December, 1974, three cases of botulism occurred in a family; two were fatal. The first patient died after a 10-day illness without botulism being suspected. 4 days later, after a 2-day illness, the second patient was diagnosed as having botulism after a cardiorespiratory arrest; she died 3 days later. In the third patient, the only symptom was dysphagia. Clostridium botulinum type B was found in stool specimens from all three patients. Home-canned (bottled) mushrooms, which were found to contain C. botulinum type B and its toxin, were believed to be responsible for the outbreak; mushrooms were found at necropsy in the gastrointestinal tracts of both patients who died. Heat treatment of the mushrooms during canning had been inadequate.

Adult↗
PubMed1975

Low-temperature irradiation of beef and methods of evaluation of radappertization process.

An inoculated, irradiated beef pack (1,240 cans) was conducted for the determination of microbiological safety for unrestricted human consumption. Each can contained a mixture of 10(6) spores of each of 10 strains of Clostridium botulinum (5 type A and 5 type B), or a total of 10(7) spores/can. The cans were irradiated to various doses (100 cans/dose) with 60Co gamma rays at -30 +/- 10 C, incubated at 30 +/- 2 C for 6 months, and examined for swelling, toxicity, and recoverable botulinal cells. The minimal experimental sterilizing dose based on nonswollen, nontoxic sterile cans were 2.2 less than experimental sterilizing dose based on nonswollen, nontoxic sterile cans was 2.2 less than experimental sterilizing dose less than or equal to 2.6 Mrad. Using recoverable cells as the most stringent criterion of spoilage, and assuming the conventional simple exponential (without an initial shoulder) rate of spore kill, the "12D" dose was 3.7 Mrad when estimated on the basis of mixture of 10 strains totaling 10(7) spores/can, and 4.3 Mrad if it is assumed that each can of beef contained 10(6) spores of a single most resistant strain and all of these spores were of identical resistances. However, an analysis of the data by extreme value statistics indicated with 90% confidence that the spore death rate was not a simple exponential but might be a shifted exponential (with an initial shoulder), Weibull, lognormal, or normal, with a "12D" equivalent of about 3.0 Mrad regardless of the initial spore density per can. There was an apparent antagonism between the irradiated type A and B strains in the cans. Some of the cans contained type B toxin but did not include type B viable cells. Other cans had a mixture of type A and B toxins, but a large number of these cans did not yield recoverable type B cells. However, type A viable cells could always be demonstrated in those cans containing type A toxin.

Animals↗
PubMed1975

Methods for isolation of anaerobes in the clinical laboratory.

Major points to be emphasized include: 1) Anaerobes are very numerous in nature, but only a relatively small number of species are commonly associated with disease in man; 2) The majority of anaerobic bacterial infections involve endogenous rather than exogenous microorganisms, and the patients are usually compromised in some manner prior to infection; and 3) Success in isolating anaerobic bacteria requires careful performance and control of each step in the isolation procedure. These steps include selection and collection of clinical specimens, microscopic examinations, selection and use of primary isolation media, use of anaerobic systems, incubation of cultures and subculture of colonies to obtain pure culture isolates.

Anaerobiosis↗
PubMed1974

Susceptibility of Clostridium ramosum to antimicrobial agents.

The susceptibility of 49 strains of Clostridium ramosum to 10 antibiotics was determined by agar dilution and disk diffusion tests. Results showed that, among the anaerobes, C. ramosum is second only to Bacteroides fragilis in its resistance to antimicrobial agents. All strains were susceptible to penicillin, carbenicillin, chloramphenicol, vancomycin, and metronidazole at readily achievable blood levels. Most strains (83%) were susceptible to erythromycin. There was a high level of resistance to clindamycin in 16% of the strains. All isolates were resistant to rifampin and gentamicin, and most were resistant to lincomycin. Assessment of susceptibility by measurement of inhibition zone diameters with disk diffusion tests was not satisfactory.

Anti-Bacterial Agents↗
PubMed1974

Effect of culture medium and carbon dioxide concentration on growth of anaerobic bacteria commonly encountered in clinical specimens.

Representative strains of anaerobic bacteria from human infections were used to evaluate broth media, gas mixtures, and inocula for use in developing a procedure for performing minimal inhibitory concentration antimicrobic susceptibility tests. Nine commercially available media, including two that were chemically defined, were tested. Tests were performed in atmospheres with carbon dioxide concentrations between 2.5 and 10% and also in the GasPak system (BBL) that had a disposable hydrogen-carbon dioxide generator. Growth curves on each organism grown in schaedler broth and a 5% carbon dioxide atmosphere were used to determine growth characteristics, equate time of the particular growth phases to turbidity readings, and determine the numbers of viable organisms present in the culture. Schaedler broth proved to be most advantageous in combination with an atmosphere of 5% carbon dioxide, 10% hydrogen, and 85% nitrogen. The growth curve studies yielded valuable data on the rapidity and quantity of growth under these conditions. We believe these data have provided information which can be used as the basis for developing a standardized procedure for antimicrobic susceptibility testing for anaerobic bacteria.

Anaerobiosis↗
PubMed1973

Micromethod system for identification of anaerobic bacteria.

A micromethod multitest system prepared by Analytab Products, Inc. and conventional tests employed at the Center for Disease Control for identification of anaerobes were compared. All procedures were conducted in an anaerobic glove box. A total of 104 cultures, including 18 reference strains and 86 diagnostic cultures, were examined. Ninety-one percent of the total tests performed with the two systems were in agreement. Greater than 90% agreement between the two systems was obtained with 12 of the 17 differential tests compared. The tests for nitrate reduction and H(2)S production gave the poorest agreement, 77.8 and 80.8%, respectively. Only 66% of the 86 diagnostic cultures could be presumptively identified with the micromethod system supplemented only with microscopy and colonial characteristics. However, when appropriate supplementary tests and gas-liquid chromatography were used with the micromethod system, 85% of the 86 strains could be identified. When Ehrlich reagent, instead of Kovac reagent, was used with the micromethod to test for indole, the agreement in identification was raised to 93%.

Anaerobiosis↗