non-Salmonella Isolates Research Articles

Detection of Salmonellae and Other Enterobacteriaceae by Commercial Deoxyribonucleic Acid Hybridization and Enzyme Immunoassay Kits

Cultures of 294 Salmonella and 100 other Enterobacteriaceae isolates were comparatively analyzed by the GENE-TRAKRSalmonella Assay, the ReportRSalmonella Visual Immunoassay, and the Organon Teknika Salmonella-TekR assay. Of the Salmonella isolates, 99.0% were reactive in the GENE-TRAK assay, 98.0% were reactive in the Report assay and 100% were reactive in the Organon Teknika assay. The three strains missed by the GENE-TRAK method belonged to Salmonella subgenus V. Four of seven strains that were nonreactive by the Report assay were nonmotile isolates; some nonmotile isolates were reactive. Of the non-Salmonella isolates assayed, 6.0% were consistently positive by the Report Method and 16.0% were consistently positive by the Salmonella-Tek method, while none were consistently positive by the GENE-TRAK method. Variable assay results were obtained with 19.0% of the strains using the Report assay, 20.0% of the strains in the Salmonella-Tek assay, and 7.0% of the strains by the GENE-TRAK assay.

Multitest System for Biochemical Identification of Salmonella, Escherichia coli, and Other Enterobacteriaceae Isolated from Foods: Collaborative Study

Nine laboratories evaluated the ability of the MICRO-ID test system to correctly identify members of the Enterobacteriaceae. A total of 78 isolates representing 11 genera of enterics that had been previously isolated from foods were used in the collaborative study. The collaborators streaked each isolate on plate count agar and incubated the plates overnight at 35 degrees C to check purity of the isolates. Then they proceeded with the method in which an isolated colony is transferred to a plate count agar slant and is incubated 18-24 h at 35 degrees C. Growth from the slant is emulsified in 3.5 mL physiological saline to a density comparable to a McFarland No. 2 tube and is then used to inoculate the test (MICRO-ID) strip. The strip is incubated 4 h at 35 degrees C and the reactions are read and recorded. Isolates are identified by using an octal code and the test kit manual. The system correctly identified 98.8% of the Salmonella isolates, 97.7% of the E. coli isolates, and 84.6% of the other 9 enteric genera tested. The system has been approved interim official first action as an alternative to conventional biochemical tests (1) for presumptive generic identification of food-borne Salmonella and for screening and elimination of non-Salmonella isolates; (2) for identification of E. coli from foods; and (3) for presumptive generic identification of other Enterobacteriaceae isolated from foods.

New semisolid agar for the detection of motile salmonellae

A semisolid selective motility agar based on selenite broth and designated semisolid selenite fecal (SSF) agar was developed for recovery of motile salmonellae from large numbers of rodent fecal specimens. The medium is easily prepared and inoculated; results are readily interpreted. When combined with selenite or gram-negative broth enrichment, SSF agar yielded significantly better Salmonella isolation from experimentally infected rodents than a standard battery of media. Only 14 non-Salmonella isolates from 1,002 Salmonella-free rodent fecal specimens migrated on SSF agar.

Comparative Accuracy of Five Biochemical Systems for Identifying Salmonella and Related Foodborne Bacteria: Collaborative Study

The comparative accuracy of 4 biochemical diagnostic kits (API, Enterotube, Minitek, and Pathotec) and the conventional (AOAC) tube system for identifying primarily Salmonella and other enteric isolates was collaboratively studied. Each of 11 participating analysts received 40 foodborne isolates (25 Salmonella and 15 non-Salmonella cultures), representing a total of 440 cultures examined by each identification system. In decreasing order of accuracy, the overall number of correctly identified cultures with each of the systems was as follows: AOAC, 423 (96.1%), Minitek, 403 (91.6%), Enterotube, 395 (89.8%), API, 394 (89.5%), and Pathotec, 373 (84.8%). A cost analysis showed that all 4 diagnostic kit systems were less expensive than the conventional AOAC tube system for a single culture identification. Three of the diagnostic kits have been adopted as official first action as alternatives to the AOAC biochemical tube system for presumptive generic identification of foodborne Salmonella and for screening and eliminating non-Salmonella isolates. Routine incorporation of any one of the 3 diagnostic kits, however, should be preceded by the demonstration in the analyst's own laboratory of adequate correlation between the kit and the AOAC system.

Evaluation of a Selective Medium for Hydrogen Sulfide Production by Salmonella

An evaluation was made of Padron-Dock-Stader sulfide (PDS) agar for the rapid detection of Salmonella and Arizona microorganisms in foods. Analysts from 9 Food and Drug Administration District laboratories determined the reaction of 638 Salmonella cultures, 30 Arizona cultures, and 1754 non-Salmonella and non-Arizona cultures isolated from 157 food samples in PDS agar. The degree of positive reactions of these cultures in this agar was scored on a scale of "-" to "+++". The highest percentage of Salmonella isolates (64.1%) was in the category of +++ reactions. Progressively lower percentages of Salmonella isolates occurred in the more negative reaction categories. The highest percentage of Arizona isolates (66.7%) occurred in the intermediate ++ category. The majority of non-Salmonella and non-Arizona isolates occurred in the minus (41.0%) and plus or minus (44.8%) categories. Advantages of using the PDS agar are that it is simple to use, requires no specialized training or equipment, and alerts analysts to those Salmonella cultures which produce atypical reactions in triple sugar iron agar particularly the lactosepositive Salmonella. However, in this study the occurrence of false-negative reactions ranged from 4.3 to 13.9% for Salmonella and from 0 to 6.7% for Arizona, according to the criteria used to interpret the reactions in PDS agar.