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Comparison of the reliability and sensitivity of three serological procedures in detecting antibody to Yersinia pestis (Pasteurella pestis).

Three serological procedures, the agar-gel precipitin inhibition, the complement fixation, and the indirect hemagglutination tests, were used to detect and measure antibody to Yersinia pestis in the sera from 383 individuals. Although all three tests were useful in detecting plague antibody, the most reliable and sensitive test procedure was indirect hemagglutination.

Agar↗

Biochemical and physical changes in shaken suspensions of Pasteurella pestis.

Pasteurella pestis, harvested after 24 to 30 hr of growth in a casein hydrolysate medium at 26 C, was resuspended and shaken in 3% lactose-0.1 m phosphate buffer for 4 hr at the same temperature. Certain characteristics of these starved cells were compared with those of control cells. No differences in the amounts of cellular carbohydrate or lipid were detected. The concentrations of the principal free amino acids were greater in the shaken cells, except that they contained no measureable arginine, and the normally large pools of intracellular tricarboxylic acid cycle intermediates were reduced. Greater viable-cell counts resulted with the cells that were shaken in lactose buffer than with the control cells when each was incubated at 5 C for several weeks. However, the reduced viabilities were apparent losses caused by the formation of aggregates of cells. The clumping of cells was caused by the polymerization of extracellular nucleic acids, principally deoxyribonucleic acid, that were excreted by the cells. Cell clumping could be partially prevented by prior shaking of the suspended cells, which removed some of the deleterious material, or by the action of crystalline deoxyribonuclease.

Acids↗

Use of the antiserum-agar plate technique for specific identification and isolation of Pasteurella pestis.

Pasteurella pestis colonies were specifically identified on antiserum-agar plates used for primary culture of tissues from experimentally infected guinea pigs. Both selective and nonselective antiserum-agar plates were used to identify P. pestis from guinea pigs kept at 22 C for periods up to 4 days after death from plague. Colonies identified as P. pestis on selective and nonselective antiserum-agar plates, by the appearance of precipitin rings following brief chloroform vapor treatment, remained viable and were subsequently purified on nonselective antiserum-agar plates. Isolates obtained in this manner were uniformly lethal when injected into mice and guinea pigs, and conformed to standard laboratory criteria for P. pestis. P. pestis was identified on selective antiserum-agar plates from the spleens of all guinea pigs killed by the isolates, and from a large majority of the mice. The practical value and confirmative nature of the method were demonstrated.

Animals↗

Anti-Pasteurella pestis factor. 3. Effects of fatty acids on Pasteurella pestis.

The bactericidal activity and the chemical and physical characteristics of lipid fractions of extracts from organs of normal mice and guinea pigs have been described previously. The present study describes the effects of commercially prepared fatty acids which are representative of those found in the extracts. Saturated fatty acids with 12, 14, and 16 carbon atoms and unsaturated fatty acids with more than one double bond were the most effective in killing Pasteurella pestis. Tweens 20 and 80, Spans 40 and 80, and some of the methyl esters of the fatty acids did not strongly inhibit P. pestis. It was concluded, therefore, that both the length of the carbon chain and the presence of the carboxyl group of the free fatty acids were important in their effects on P. pestis. Neither the very active lauric acid nor the relatively inactive oleic acid appeared to severely alter the morphology of P. pestis. Supernatant fluids from incubated mixtures of sodium laurate or sodium oleate and cells did not contain significantly greater concentrations of proteins or nucleic acids than did the controls. These observations do not preclude an alteration of the permeability of the cell walls.

Caproates↗