Ritsuko Murakami

Enterotoxigenicity and Tetracycline Resistance of Clostridium perfringens Isolated from Chicken

Fifty chickens prepared for sale and 15 samples each of minced and non-minced chicken for use as raw material for processed food were collected and strains of Clostridium perfringens were isolated from them. The number of isolates was 153 and the isolation frequencies of the organism from these 3 kinds of samples were 34%, 100%, and 87%, respectively. Among these 153 isolates, there were 32 strains that were extraordinarily resistant to heat; 30 of the 32 strains were resistant to 100°C for 10 minutes, and the other 2, to 100°C for 60 minutes. However, no enterotoxigenicity was found with these 32 strains, though 1 strain was found to be enterotoxigenic by reversed passive hemagglutination tests.The MICs of tetracycline for 114 selected strains were examined by the plate dilution method. Strains resistant to 12.5μg/ml of tetracycline amounted to 84 of the 114 strains, and 53 of these 84 strains were found to be highly resistant to the drug with MICs of more than 25μg/ml. Tetracycline resistance-transfer experiments were carried out using 53 highly resistant strains as donors and 2 recipient strains which are maintained in our laboratory. Transferable tetracycline R-plasmids were detected in 41 of the 53 highly resistant strains.Tetracycline R-plasmids were extracted from these transcipients and treated with the restriction endonuclease, EcoRI. Several different restriction profiles were observed among the plasmids.

In the Ethanol Colorimetric Determination of Sorbic Acid in Foods

Sorbic acid in foods was extracted by dialysis, then 0.1M nitric acid and 1% iron (III) nitrate soln. were added to the extract and the mixture was heated in a boiling water bath. Next, thiobarbituric acid (TBA) was added to the reaction mixture in the boiling water bath and heated for 10 minutes. The reaction mixture was cooled to room temperature and the absorbance at 532nm was measured.It was found that this method could be applied to foods containing ethanol without difficulty and was not disturbed so much by other food additives probably used with sorbic acid. Thus, sorbic acid in various commercial foods could be determined in a short time by this method.