SALMONELLOSIS 





A) 



* COMPARISON OF WET COMPOSITING WITH STANDARD METHODS FOR DETECTING SALMONELLAE IN 

 ANIMAL BY-PRODUCTS. Harrington, R., Blackburn, B. 0. and Murphy, C. D. (Project Report) 



o* 



Summary 



Three wet compositing techniques were compared with a standard procedure to determine the efficiency of 

 wet compositing for the detection of salmonellae in samples of animal by-products. There was no significant 

 difference («0.05) in the proportion of lots found by the four methods. 



Introduction 



In a previous repqrt on dry compositing, a method was described for the examination of pooled animal 

 by-product samples (3). 1 When the compositing methods were compared with a standard culture procedure, there 

 was no significant difference between two of the compositing methods and standard culture. However, one 

 compositing method appeared to be less sensitive than the standard methods. 



The purpose of this study was to evaluate wet compositing as an approach for the isolation of salmonellae 

 from samples of animal by-products. 



This is a report on the comparison of a standard culture procedure (1) with wet compositing techniques for 

 the isolation of salmonellae from animal by-products. 



Materials and Methods 



Animal by-product samples: Samples were obtained from rendering plants in Illinois, Indiana, Iowa, Kansas, 

 Minnesota, Nebraska, North Dakota and South Dakota by Animal and Plant Health Inspection Service field 

 personnel. 



Mediums: Triple sugar iron (TSI) agar and lysine iron (LI) agar were prepared according to the instructions of 

 the manufacturer. 2 Tetrathionate (TT) broth and brilliant green sulfadiazine (BGS) agar were prepared according to 

 the methods previously described (1). Mannitol-tergitol (MT) broth was prepared by adding 20 g of tryptose, 2 5 g of 

 sodium chloride, 5 mg of thiamine hydrochloride, and 10 g of d-mannitol 3 per liter of distilled water. Following 

 sterilization at 120 C for 15 minutes, 6 ml of a 10 percent solution of Tergitol Anionic 7 4 was added. 



Culture Methods: A total of 600 samples of animal by-products were grouped to form 60 lots (10 samples per 

 lot) and culture procedures were performed on one lot at a time. Each of the 10 samples in the lot was thoroughly 

 mixed and two 30 g aliquots were removed and identified as "1" and "2." The 10 number-1 aliquots were used to 

 form composites A t and A 2 while the 10 number-2 aliquots were used for the standard procedure and composite B. 



The number-1 aliquot of each of the 10 samples in the lot was placed in a separate wide mouth screw cap jar 

 and 250 ml of MT pre-enrichment broth was added. These were incubated for 18-24 hours at 37 C. 



Composite A! was formed by removing 1 ml from each of the MT broth cultures and transferring it to a test 

 tube containing 10 ml of double strength TT broth. Following overnight incubation at 37 C, a 5-6 mm loopful of 

 the TT broth culture was streaked on BGS agar plates. Salmonella-type colonies appearing on the agar plates after 

 18-24 hours incubation were transferred to TSI and LI agar slants. Cultures producing reactions characteristic of 

 Salmonella sp. were verified with polyvalent "H" antiserum according to methods previously described (2). 

 Salmonella sero typing was performed on each isolate. 



Numbers in parentheses refer to References at the end of this report. 



Difco Laboratories, Detroit, Mich. 



BBL, Division of BioQuest, Division of Becton Dickenson Co., Cockeysville, Md. 



Union Carbide Chemical Co., Division of Union Carbide Corporation, New York, N.Y. 



37 



