SUXNARY.A strain of h'almonella aenftenberg and a strain of Salm. bedford have been found with D,,. values similar to that of the classical heat resistant salmonella, SaZ,m. acnftenberg strain 776W. The resistanoes of the two heat resistant serotypes and two heat sensitive strains of these serotypes was determined in heart infusion broth containing increasing amounts of suarose, sodium chloride or glycerol. The observed changes in heat resistance could not be related directly to the aw of the heating menstruum. It is impossible t o predict from such studies the heat resistance of salmonellae in foods of low a , .
A rapid 18 hr. technique has been developed for detecting salmonella contaminated carcass and boneless meats. It is based on 43° C. selenite enrichment of samples, followed by immunofluorescent detection of salmonella cells in the enrichment. In tests with 286 meat samples the rapid and conventional techniques agreed in the detection of 93 positive and 149 negative samples. The two tests failed to agree for the remaining 44 samples. The rapid technique thus lacks precision, but could be used as a rapid ‘presumptive’ salmonella test, so that contaminated material could be prevented from reaching the processing lines of food factories.We thank Dr Betty Hobbs of the Food Hygiene Laboratory for kindly sup plying the meat samples used in this investigation, Dr Patricia Bradstreet of the Standards Laboratory for Serological Reagents for the salmonella diagnostic antisera and Mr R. Kenworthy for performing the goat injections.
A rapid 18-24 h immunofluorescence technique detected 14 of 16 positive samples in tests on 706 routine samples, which included 666 home produced raw beef aamples. The rapid technique also recorded 49 false positive results, i.e. samples which proved negative in subsequent cultural tests. The immunofluorescence technique could be used aa a presumptive screening test aimed a t the rapid detection of negative samples. In this way salmonella free raw materials should usually be cleared for production within 1 day of sampling.
Samples (2208) of food raw materials and products were examined for the presence of salmonellae by use of conventional salmonella, detection procedures and the enrichment serology (ES) techniques described by Sperber & Deibel (1980); 348 samples were positive for salmonellae by the conventional procedures. Using the ES technique with a 24 h elective enrichment step, 93-98% of samples positive by the conventional procedures were also positive by the ES technique. Selective enrichment of food samples using tetrathionate broth containing novohiocin, incubated at 41 ', led to the best recovery of salmonellae by both the conventional and ES techniques. ENRIUHMENT S E R o L o w , an accelerated procedure for detecting salmonellae in foods, was described by Sperber t Deibel in 1969. This involved pre-enrichment and * Enrichment serology with 24 h elective enrichment. b Selective enrichment followed by plating on brilliant green agar after 24 h or 48 h. 0 Not tested.
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