One-day fluorescent-antibody procedure for detecting salmonellae in frozen and dried foods

The indirect fluorescent-antibody technique was used to examine 422 food samples for the presence of salmonellae. A cultural phase involving a 16-hr preenrichment in buffered nutrient broth-milk medium followed by a 4- to 5-hr subculture into fresh medium of the same composition was evaluated. This procedure yielded a sufficient population of salmonellae so that no false-negative results were obtained. Of the 31 false-positives obtained, 12 samples yielded positive cultural results upon extensive subculture of the original enrichment broths. Yeast cells and both vegetative and spore forms of bacilli were observed to fluoresce when stained with anti-Salmonella serum. Efforts to ascertain the cause of these cross-reactions and several alternate explanations are discussed.

The distribution of large dividing lymph node cells in syngeneic recipient rats after intravenous injection

The distribution of large dividing lymph node or thoracic duct lymph cells, labeled in vitro with (3)H-thymidine, was studied in syngeneic recipient rats after intravenous injection. In most experiments the donor rats had been immunized with Bacillus pertussis 4 days earlier, but in some instances cells from nonimmunized donors were used. In smears, the labeled donor cells had the appearance of large lymphocytes or large pyroninophilic cells. By electronmicroscopy, the majority of labeled donor cells were seen to have only scanty endoplasmic reticulum. It was found that the labeled cells rapidly "homed" to lymphoid tissue and recirculated in the recipient, in a fashion resembling that of small lymphocytes. However, the distribution of labeled cells was found to depend upon the source of the donor cells. Cells from mesenteric lymph nodes or thoracic duct lymph showed a marked preferential accumulation in lymphoid tissue within or adjacent to the intestine, whereas cells from peripheral nodes accumulated preferentially in peripheral lymph nodes. Cells from any of these sources showed an equal tendency to accumulate in the white pulp of the spleen. Suspensions of small lymphocytes, labeled in vitro with (3)H-uridine, did not display a similar tendency to localize preferentially in lymphoid tissue in certain regions. It was also found that large dividing lymph node cells from donors immunized with an antigen (2,4-dinitrophenyl-bovine gamma globulin (DNP-BGG) or B. pertussis) showed a greater tendency to accumulate in a recipient lymph node containing that antigen than in the contralateral node. It was not determined whether the selective accumulation of large dividing lymphoid cells from different sources in lymphoid tissue of different regions in recipients was due to an antigen recognition mechansim or was the result of two different populations of cells with different "homing" mechanisms.

Application of the fluorescent-antibody technique to an ecological study of bacteria in soil

The fluorescent-antibody technique was used to identify cells and spores of Bacillus subtilis and cells of B. circulans from soil. From cells grown in three broth media of different nutrient status, i.e., a cold extracted soil medium (CSE), an unamended autoclaved soil extract (HSE), and nutrient broth (NB), antisera were produced with both quantitative and qualitative differences in antibody content. The specificities of antisera to two strains of each of the Bacillus species were determined. Antisera for B. subtilis O antigens were species-specific and showed no cross-reactions, whereas those for the B. circulans O antigens were strain-specific and in some cases showed cross-reactions with B. alvei. This cross-reaction was removed by absorption of the antiserum with B. alvei O antigen. Fluorescein isothiocyanate gamma-globulin conjugates prepared from these antisera showed the same specificity reactions. A method for staining bacteria on soil particles was developed, by use of small staining troughs. By mounting stained soil particles on slides and irradiating them with transmitted and incident ultraviolet blue light, bacteria on both mineral and organic particles, taken directly from soil, could be observed. Fluorescent antibodies against cells grown in CSE gave brighter fluorescence of stained bacteria on soil particles than did fluorescent antibodies against cells grown in either HSE or NB. Colonies of both Bacillus species were generally small and localized. Spore antisera, though not rigorously tested for specificity, were used to identify spores of B. subtilis on soil particles. The uses and implications of the technique in soil bacteriology are discussed.

Characteristics of Tphi3, a bacteriophage for Bacillus stearothermophilus

A bacteriophage (Tphi3) which infects the thermophilic bacterium Bacillus stearothermophilus ATCC 8005 was isolated and characterized. Infection of the bacterium by the bacteriophage was carried out at 60 C, the optimal growth temperature of the host. At 60 C, the phage had a latent period of 18 min and a burst size of about 200. The phage was comparatively thermostable in broth. The halflife of Tphi3 was 400 min at 60 C, 120 min at 65 C, 40 min at 70 C, and 12 min at 75 C. The activation energy for the heat inactivation of Tphi3 was 56,000 cal. The buoyant density of Tphi3 in a cesium chloride density gradient was 1.526 g/ml. Electron micrographs of Tphi3 indicate that the phage has a head that is 57 mmu long. The dimensions and shape of the head are compatible with those of a regular icosahedron. Each edge of the head is 29 mmu long. The tail of Tphi3 is 125 mmu long and 10 mmu wide. There are about 30 cross-striations that are spaced at 3.9-mmu intervals along the tail. Under the conditions investigated, Tphi3 adsorbed slowly to the host. Only 2.8% of the phage adsorbed in 10 min at 60 C, the normal incubation temperature that was used. Tphi3 was not infective to four other thermophilic strains or to two mesophilic strains of bacteria.