Cell classification by laser light scattering: identification and separation of unstained leukocytes

We have used a flow-system cell sorter to separate unfixed, unstained human leukocyte cells into morphologically distinct populations based only on the intensity of 488-nm wavelength laser light simultaneously scattered by each cell at two different angles. Three populations were observed as distinct peaks in a two-parameter pulse-height distribution and were then physically sorted into separate classes and stained for cytological examination. The three groups consisted of lymphocytes, monocytes, and neutrophils. Each group contained between 77 and 98 per cent of a single cell type. Blood from an irradiated monkey was also sorted and showed the presence of a fourth peak which consisted of 61 per cent eosinophils. Thus, multiangle light-scattering information from unfixed, unstained cells may be a promising technique for rapid morphologic analysis and may have application, for example, as a highspeed automated leukocyte differential. We anticipate that this method may be useful in other clinical applications where morphologic differences are diagnostically important. One of the principal advantages of the method is elimination of fixation and staining of the samples; this is a nondestructive testing technique.

The moroccan food snail, Helix aspersa, as a source of Salmonella

A total of 270 samples, nine lots of 30 samples each, of imported Moroccan food snails was examined for the presence of Salmonella. Eighty-four samples (an overall incidence of 31.11%) and all nine lots contained Salmonella. No significant difference (P greater than 0.25) in the number of positive samples was observed by using either selenite cystine both or tetrathionate broth when the samples had been pre-enriched in lactose broth. When used as direct selective enrichments with samples not pre-enriched in lactose broth, tetrathionate broth was significantly (P less than 0.05) more productive than selenite cystine broth. The overall detection of Salmonella-positive samples by direct enrichment was significantly greater (P less than 0.001) than by pre-enrichment. A variety of uncommon serotypes occurrence and incidence, and the concomitant human health potential, of Salmonella in one species of live, imported food snails.

Media to Improve Flagellar Development for Salmonella Flagellar (H) Test

An increasing number of salmonellae, isolated and examined in 1969, failed to give a positive flagellar (H) reaction upon initial testing. After passage through motility medium, the majority of these cultures were positive when retested using the AOAC Salmonella serological flagellar test procedures. Improved detection of flagellar antigens was obtained by using a medium consisting of equal portions of Trypticase Soy and tryptose broths and a small amount of yeast extract. The improvement in the flagellar agglutination test usually occurred without passing the culture through motility medium. The substitution of the improved flagellar broth for tryptophane broth in the AOAC 24 hr Salmonella polyvalent, 41.039, or Spicer-Edwards flagellar, 41.040, tests has been adopted.

Detection and Identification of Salmonella from Dry Milk: Report of a Collaborative Study

A method for the detection and identification of Salmonella from dry milk was subjected to collaborative study. A 100 g sample is reconstituted in 1 L distilled water with 2 ml 1% aqueous brilliant green dye, incubated, subcultured in selenite cystine broth and tetrathionate broth, incubated, and streaked on selective plates of brilliant green agar, Salmonella-Shigella agar, and bismuth sulfite agar. After incubation, suspicious colonies can be further identified by biochemical and serological tests. Samples of nonfat dry milk and dry whole milk, some inoculated with Salmonella binza, Salmonella tvorthington, and Citrobacter, were examined by 30 collaborators. Results from 23 of 28 collaborators were in agreement; the method will detect and identify Salmonella from positive nonfat dry milk and dry whole milk. The method is recommended for adoption as official first action.