This paper is a critical review of the "drop piate" method of determining the number of viable bacteria in fluids, together with a description of an experimental comparison of the "drop plate" with the more usual "pour plate" procedure.It is shown that counts on pure cultures of bacteria made by the "drop plate" method are some 7 /6 higher than those made on the same cultures by the "pour plate" method. It is also shorvn that the standard error of a series of counts made by the "drop plate" procedure is slightly less than for those made by the "pour plate" method.A successful "drop plate" method of determining the number of viable bacteria in fluid suspension has been in use for a number of years in several English research laboratories. Considerable experience with the method suggests the desirability of reviewing the procedure both as a research tool and for routine assays of such material as milk.Donald (2) introduced a method for the precise measurement of fluid volume by means of drops. This depends upon the fact that the size of a drop delivered from a pipette is governed, other factors being constant, by the erternal diameter of the dropping tube. Fildes and Smart (3) expanded the procedure and developed methods of preparing and calibrating the pipette. Several authors have described in brief form the adaptation of dropping pipettes to the technique of plate counts of bacteria, particularly Wilson (9), Aitken, Barling, and Miles (1), Kenny, Johnston, von Haebler' and Miles (5), von Haebler and Miles (4), Miles, Misra, and Irwin (7), and Snyder (8). The last two papers include a statistical analysis of the accuracy of the method.The plating procedure consists simply in adding, with a calibrated dropping pipette, drops of properly diluted suspensions of bacteria to the surface of nutrient agar or other appropriate medium in Petri plates. The surface of the medium must be dried to the stage where a drop of bacterial suspension will spread over an area of 1.5 to 3 cm. in diameter and permit absorption of the fluicl of the drop in 15 to 20 min. On incubation the area covered by a drop of suitably diluted suspension will develop well spaced surface colonies that permit rapid and accurate counts. Droppi,ng PipettesThese are made, as described glass tubing to form two pipettes Methods by Donald, by drawing a length of 7 mm. rvith long, very gradual tapers.
Ustilagic acid is shown to be relatively inactive against common Gram-positive and Gram-negative pathogenic bacteria and against Mycobacterium tuberculosis. Serum and urine levels in rabbits following oral administration are much lower than the concentration required for in vitro inhibition of most bacteria tested. Human serum depresses the antibacterial effect of ustilagic acid in vitro. The drug had no effect on the course of experimental infection in mice.
The use of peripheral blood leukocytes in the capillary-migration test is presently a very active area of investigation. A technique was developed in our laboratory which made possible the use of rabbit leukocytes in this in vitro test for cellular reactivity. Using a combination of gelatin sedimentation and sucrose-density gradient centrifugation, it was possible to harvest white cell populations from 59 rabbits which had median percentages of 74% mononuclear cells and 26% granulocytes with a median percent recovery of 34% of cells for the entire group. When testing cell populations from rabbits sensitized with killed mycobacteria, significant inhibition of migration was found when particulate antigen was included in the tissue-culture medium. Purified Protein Derivative (PPD) failed to elicit a similar response under the same conditions of experiment. Migration inhibition was also found when cells from animals immunized with ovalbumin were tested in the presence of specific antigen.
The design for the reconnection of SN-216 to U-D valve pit was reviewed on May 24, 1999. A l l Review Comment Record coments were resolved and closed at this meeting. The review concluded that the reconnection of SN-216 to U-D valve pit was acceptable. The design was approved with the incorporated comments as recorded on the RCR's. No outstanding comments remain. TRADEMARK DISCLAIMER. Reference herein to any specific commercial proddct, process, or Sewice by trade name, trademark, manufadurer, or otherwise. does not necessanly constitute or imply Rs endorsement, remmmendation. or favoring by the United States Government orany agency thereof or its contractors or subcontractors.
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