Ten different Salmonella serotypes were grown in a chemically defined medium supplemented with 0.01% yeast extract. After sedimentation of the cells by centrifugation, flagella were detached by exposure to pH 2 for 30 min at room temperature. The flagellaless cells were removed by centrifugation, and the flagellin in the supernatant was further purified by high-speed centrifugation, ammonium sulfate precipitation, and dialysis in 50,000-molecular-weight-cutoff tubing. The 10 flagellin preparations were of a high degree of purity, as demonstrated by electron microscopy, sodium dodecyl sulfate-polyacrylamide gel electrophoresis, and measurement of salmonella H and O agglutination titers of antisera raised in rabbits with the flagellin preparations as immunogens.

No abstract

Ten antisera raised in rabbits, against polymeric flagellins from ten different Salmonella serotypes were used to determine the relative cross-activities between salmonella flagellins in monomeric form. The results showed a high degree of cross-reactivity between the antisera (IgG antibodies) and all monomeric flagellins investigated. Consequently, it was possible to detect the ten Salmonella serotypes, after heat depolymerization of flagella using radioimmunometric assay with only one antiserum raised against polymeric flagellin from one serotype. The results also showed that native flagella differed antigenically from repolymerized and monomeric flagellins. This is possibly due to changes in the tertiary structure of sub-units of flagella when depolymerized with acid or heat resulting in unfolding and unmasking of common antigenic determinants. The unfolded and unmasked antigenic determinants were not only common to the Salmonella serotypes investigated, but also to other members of Enterobacteriaceae.

Twelve cheese batches were made with variable starter activity, from milk inoculated with Staphylococcus aureus. At the end of cheddaring, only half the curd of each batch was salted and each portion was then pressed separately, cut and stored at 11 and 4 C for 6 weeks. Changes in bacterial counts, pH, enterotoxin A concentration and organoleptic properties were monitored. At the end of cheddaring, enterotoxin was detected in batches made with large initial inocula of S. aureus and/or low starter activities. At the end of pressing, the count of S. aureus, pH and enterotoxin concentration in the unsalted cheese (USC) were significantly lower than in salted cheese (SC), due to the adverse effect of salting on growth of microorganisms other than S. aureus. No change in enterotoxin concentration was detected in USC during storage at 11 and 4 C, and a sharp decline in S. aureus count occurred. The rate of such decline at 11 C exceeded that at 4 C. Increases in S. aureus count and enterotoxin concentration occurred in some SC batches stored at 11 C, whereas a slight decrease in S. aureus count and no change in enterotoxin concentration occurred in all SC stored at 4 C. At the end of storage, no cheeses had gas defects or significant flavor defects, which could have prohibited further processing.

Native flagella of ten Salmonella serotypes were shown to possess serotype-specific antigenic determinants as well as a multiple of common antigenic determinants, which varied in concentration. Each common antigenic determinant was shared by certain, but not all, serotypes. This has been demonstrated from agglutination and radioimmunometric assay (RIMA) results, using ten antisera raised in rabbits against purified polymeric flagellins from ten Salmonella serotypes as immunogens. The minimum detectable populations of salmonellae, as determined by RIMA varied considerably, due to variation in concentrations (and possibly types) of common antigenic determinants. However, the results demonstrated the feasibility of utilizing RIMA for the qualitative detection of salmonellae, using a mixture of only the ten antisera and 125I-labelled protein A as a general tracer. In this way, 77 different salmonellae were detected in less than 8 h after culturing in selective broth. The RIMA developed was specific for salmonellae and showed no cross-reactions with high populations of other members within the family Enterobacteriaceae.